Treatment appears in FNA Volume 24. Treatment on page 486.

Plants annual or perennial; usually synoecious, sometimes monoecious, gynodioecious, dioecious, and/or asexual; with or without rhizomes or stolons, densely to loosely tufted or the culms solitary. Basal branching intravaginal, pseudointravaginal, or extra vaginal; prophylls of intravaginal shoots 2-keeled and open, of pseudointravaginal shoots not keeled and tubular, of extravaginal shoots scalelike. Culms 1-150 cm, hollow, usually unbranched above the base. Sheaths from almost completely open to almost completely closed, terete or weakly to strongly compressed; auricles absent; ligules membranous, truncate to acuminate; blades 0.4-12 mm wide, flat, folded, or involute, adaxial surfaces with a groove on each side of the midvein, other intercostal depressions shallow, indistinct, apices often prow-shaped. Inflorescences usually terminal panicles, rarely reduced and racemelike. Spikelets 2-12 mm, usually laterally compressed, infrequently terete to subterete, usually lanceolate, sometimes ovate; florets (1)2-6(13), usually sexual, sometimes bulb-forming; rachillas usually terete, sometimes prolonged beyond the base of the distal floret; disarticulation above the glumes and beneath the florets. Glumes usually shorter than the lowest lemma in the spikelet, usually keeled, 1-3(5)-veined, unawned; calluses blunt, usually terete or slightly laterally compressed, sometimes slightly dorsally compressed, glabrous or hairy, hairs often concentrated in 1(3) tufts or webs, sometimes distributed around the calluses below the lemmas as a crown of hairs; lemmas usually keeled, infrequently weakly keeled or rounded, similar in texture to the glumes, 5(7-11)-veined, lateral veins sometimes faint, margins scarious-hyaline distally, apices scarious-hyaline, truncate or obtuse to acuminate, unawned; paleas from 2/3 as long as to subequal to the lemmas, distinctly 2-keeled, margins and intercostal regions milky white to slightly greenish; lodicules 2, broadly lanceolate, glabrous, lobed; functional anthers (1-2)3, 0.1-5 mm; ovaries glabrous. Caryopses 1-4 mm, ellipsoidal, often shallowly ventrally grooved, solid, with lipid; hila sub-basal, round or oval, to 1/6 the length of the caryopses. x = 7.

Distribution

Ill., Ind., Conn., N.J., N.Y., Ga., Wash., Utah, Alaska, Colo., Idaho, N.Mex., Nev., Maine, N.H., Vt., Del., D.C, Wis., Iowa, Mont., Oreg., Wyo., Pacific Islands (Hawaii), Md., Mass., R.I., Fla., Calif., W.Va., Tex., La., N.C., N.Dak., Nebr., Tenn., Ala., Ark., Ariz., Kans., Ky., Mich., Minn., Mo., Miss., Ohio, Okla., Pa., Puerto Rico, S.C., S.Dak., Va., Alta., B.C., Greenland, Man., N.B., Nfld. and Labr., N.S., N.W.T., Nunavut, Ont., P.E.I., Que., Sask., Yukon

Discussion

Poa includes about 500 species. It grows throughout the world, principally in temperate and boreal regions. Sixty-one species and five hybrid species are native to the Flora region; nine species are introduced.

Poa is taxonomically difficult because most species are polyploid, many are apomictic, and hybridization is common. A variety of sexual reproductive systems are represented within the genus, but individual species are usually uniform in this regard. Apomicts derived from bisexual species usually have functional anthers; they require fertilization to stimulate endosperm (and hence seed) development. Apomicts derived from dioecious species do not require fertilization; they are normally pistillate with vestigial anthers 0.1-0.2 mm long.

Herbivores find most species of Poa both palatable and nutritious. Poa fendleriana, P. secunda, and P. wheeleri are important native forage species in western North America; P. alpina, P. arctica, and P. glauca are common components of alpine and arctic vegetation. Species of Poa sect. Abbreviatae are found near the limits of vegetation in both arctic and alpine regions.

Several introduced species of Poa are economically important. Poa pratensis is commonly cultivated for lawns and pasture, and is a major forage species in cooler regions of North America; P. compressa and P. trivialis are widely planted for soil stabilization and forage; P. annua is one of the world's most widespread weeds. Poa bulbosa has been cultivated; it is now widely established in the Flora region.

Vegetative characteristics that may be useful for distinguishing Poa from other morphologically similar genera are: the more or less straight, rather than curly, roots; two-grooved, prow-shaped blades; partially or wholly closed flag leaf sheaths; and isomorphic collar margins. Useful spikelet characteristics include: terete rachillas; multiple, relatively small, unawned florets; webbed calluses; well-developed palea keels; and the greenish or milky white intercostal regions of the paleas.

There is a strong correlation between the type of basal branching, prophyll structure, and blade development of the initial leaves. Extravaginal shoots have scalelike prophylls 0.5-3 mm long and initial leaves that are bladeless; intravaginal shoots have prominently keeled prophylls 10-50 mm long that are open on the abaxial side and initial leaves with well-developed blades; pseudointravaginal shoots develop intravaginally but have tubular, indistinctly keeled prophylls, and initial leaves with rudimentary blades.

In bulbiferous spikelets, the upper florets form a single tardily disarticulating offset or bulb, each lemma being thickened at the base and leaflike distally. The bulb falls as a unit, with or without the basal floret. The basal floret(s) may have pistils and stamens, and occasionally sets seed. Generally, there is a progression within an inflorescence, the earlier spikelets being bulbiferous and the later spikelets normal.

Callus hairs in Poa follow one of three patterns. In the most common pattern, there is an isolated dorsal tuft of crinkled or pleated hairs, the web, below the lemma keel. In a few species, additional webs may be present below the marginal veins. In the second pattern, crinkled hairs are distributed around the lemma base, but are somewhat concentrated and longer towards the back; this pattern is called a diffuse web. Webbed calluses are found only in Poa. In the third pattern, the hairs are straight to slightly sinuous, and more or less evenly distributed around the lemmas bases; calluses with such a pattern are described as having a crown of hairs.

Three named infrasectional hybrids are included in this treatment. One, Poa arida, is accounted for in the key. The other two are not. Poa xlimosa is too variable, and P. xgaspensis is known from too few specimens to make their inclusion in the key helpful. All three are described at the end of this treatment, with comments on the probable parental taxa.

Unless stated otherwise, sheath closure is measured on the flag leaf, and ligule length on the upper 1-2 culm leaves; spikelet, floret, callus, lemma, and palea measurements are on non-bulb-forming florets; floret pubescence is evaluated on the lower florets within several spikelets; length of the callus hairs refers to their length when stretched out; anther measurements are based on functional anthers, i.e., those that produce pollen, as indicated by their being plump or, after the pollen is shed, by their open sacs. For hair lengths, puberulent is to about 0.15 mm long, short-villous to about 0.3 mm long, and long-villous from 0.3-0.4+ mm long, but these are only guidelines, not discrete categories; some species are only on one end of the range, and ranges have not been confirmed for every species. Many species key more than once, due in part to infraspecific variation.

Selected References

Keys

1 Culms with bulbous bases; spikelets often bulbiferous (sect. Arenariae) Poa bulbosa
1 Culms with non-bulbous bases; spikelets sometimes bulbiferous. > 2
2 Some or all spikelets bulbiferous Subkey I
2 Spikelets not bulbiferous, florets developing normally. > 3
3 Anthers 0.1-1(1.2) mm long in all florets and well developed, or only the upper 1-2 florets with rudimentary anthers; plants annual or perennial Subkey II
3 Some anthers (1.2)1.3-4 mm long, or the florets pistillate and all anthers vestigial and 0.1-0.2 mm long, or longer and poorly developed; plants perennial. > 4
4 Plants rhizomatous or stoloniferous, rhizomes or stolons usually longer than 5 mm; basal leaves of the erect shoots with well-developed blades; plants densely to loosely cespitose or the culms solitary Subkey III
4 Plants neither rhizomatous nor stoloniferous; basal leaves of the erect shoots sometimes without blades; plants densely cespitose Subkey IV

Poa Subkey I

1 Sheaths closed for 1/10 – 1/5 their length; plants without rhizomes; calluses glabrous or with a crown of hairs, rarely webbed. > 2
2 Panicles 2-4 cm long, open; plants delicate, 15-20 cm tall; blades 0.7-1.5 mm wide; lemmas 2-3 mm long, keels crisply puberulent; calluses glabrous; plants known only from the Brooks Range in Alaska Poa pseudoabbreviata
2 Panicles 1-15 cm long, open or contracted; plants usually coarser, 10-60 cm tall; blades 1-7 mm wide; lemmas 3-8 mm long, keels villous; calluses often hairy; plants widespread. > 3
3 Basal branching all or nearly all extravaginal; calluses glabrous or webbed; plants strongly glaucous, rare, alpine and arctic Poa glauca
3 Basal branching both extravaginal and intravaginal; calluses glabrous or with a crown of hairs; plants glaucous or not, not rare, arctic to subarctic or coastal and boreal. > 4
4 Basal branching strictly intravaginal; calluses glabrous; plants densely tufted Poa alpina
4 Basal branching all or partly extravaginal; calluses glabrous or hairy; plants loosely to densely tufted. > 5
5 Panicle branches smooth or sparsely scabrous; blades folded and inrolled; lemmas loosely villous between the veins; glumes somewhat shiny, not glaucous; plants of the high arctic Poa bartzii
5 Panicle branches densely scabrous, at least distally; blades flat; lemmas glabrous between the veins; glumes not shiny, often glaucous; plants subarctic or boreal and coastal Poa stenantha
1 Sheaths closed for (1/5)1/4 - 3/4 their length; plants with or without rhizomes; calluses usually webbed, sometimes glabrous. > 2
6 Basal branching intravaginal; plants densely tufted, neither rhizomatous nor stoloniferous; calluses glabrous Poa alpina
6 Basal branching completely or partly extravaginal; plants loosely or densely tufted, rhizomatous or stoloniferous; calluses usually webbed, sometimes glabrous. > 7
7 Panicles open, longest branches (5)8-15 cm long; sheaths closed for 1/2 - 3/4 their length; plants green, not anthocyanic; plants of coastal regions of British Columbia Poa laxiflora
7 Panicles contracted to open, longest branches 1-8 cm long; sheaths closed for (1/5)1/4 - 1/2 their length; plants strongly anthocyanic; plants widespread. > 8
8 Paleas glabrous intercostally; spikelets 4-5.5 mm long, lemmas 2.5-3.5 mm long, intercostal regions glabrous; panicles contracted, sometimes opening eventually; plants slender, mostly high arctic Poa pratensis
8 Paleas puberulent or hispidulous intercostally; spikelets 5.5-12 mm long; lemmas 4.5-8 mm long, intercostal regions hairy; panicles open or loosely contracted; plants slender to stout, subarctic and coastal to high arctic. > 9
9 Paleas, if recognizable, hispidulous intercostally; glumes distinctly keeled, keels scabrous; plants stout, of subarctic coastal regions Poa macrocalyx
9 Paleas softly puberulent intercostally; glumes indistinctly keeled, keels smooth or nearly so; plants slender to stout, mainly in alpine and arctic habitats, rarely coastal Poa arctica

Poa Subkey II

1 Calluses glabrous; lemmas usually softly puberulent to long-villous on the keel and marginal veins, often also on the lateral veins, glabrous between the veins, non-alpine plants rarely glabrous throughout; palea keels smooth, usually short- to long-villous near the apices, rarely glabrous; panicle branches and glume keels smooth; plants annual, sometimes surviving for a second season, introduced, weedy species (sect. Micrantherae). > 2
2 Anthers 0.6-1(1.1) mm long, oblong prior to dehiscence; spikelets crowded or sparsely arranged on the branches; plants widespread Poa annua
2 Anthers 0.1-0.5 mm long, round to elliptical prior to dehiscence; spikelets crowded on the branches; plants uncommon outside of California Poa infirma
1 Calluses webbed or glabrous, if glabrous, the lemma pubescence not as above or the palea keels at least slightly scabrous near the apices; panicle branches and glume keels smooth or scabrous; plants annual or perennial, native, sometimes growing in disturbed habitats. > 2
3 Calluses webbed; lemma keels glabrous throughout or, if hairy on the proximal 1/2, the marginal veins glabrous. > 4
4 Culms 5-15(20) cm tall; plants alpine Poa abbreviata
4 Culms 20-126 cm tall; plants of shady forests and forest openings. > 5
5 Lemmas hairy only on the keels; branches in whorls of (2)3-5(7) Poa abodes
5 Lemmas usually glabrous, marginal veins rarely sparsely hairy at the base, hairs to 0.15 mm long; branches 1-3 per node. > 6
6 Sheaths closed for at least 9/10 their length Poa marcida
6 Sheaths closed for 1/3-3/4 their length. > 7
7 Plants perennial; panicles lax, less than 1/4 the height of the plants; second rachilla internodes shorter than 1 mm; lemma apices obtuse to sharply acute or acuminate Poa saltuensis
7 Plants usually annual, rarely longer-lived; panicles erect, 1/4-1/2 the height of the plants; second rachilla internodes longer than (1)1.2 mm; lemma apices sharply acute Poa bolanderi
3 Calluses webbed or glabrous, if webbed, the lemmas hairy on the keel and marginal veins. > 4
8 Plants annual, rarely persisting for a second season; calluses webbed. > 9
9 Anthers 1, 0.1-0.2(0.3) mm long; palea keels softly puberulent to long-villous at midlength; panicles eventually open; plants from east of the 100th meridian Poa chapmaniana
9 Anthers (1-2)3 per floret, 0.2-1(1.2) mm long; palea keels scabrous or softly puberulent to short-villous at midlength; panicles contracted or eventually open; plants from west of the 100th meridian or Texas. > 10
10 Panicles eventually open; blade apices narrowly prow-shaped; lemmas with hairs of similar length over and between the veins; palea keels scabrous or softly puberulent at midlength Poa howellii
10 Panicles contracted; blade apices broadly prow-shaped; lemmas long- to short-villous over the keels and marginal veins, glabrous or pilose between the veins; palea keels softly puberulent to short-villous at midlength Poa bigelovii
8 Plants perennial; calluses glabrous or webbed. > 9
11 Panicles open, broadly rhomboidal to pyramidal, branches divaricately ascending to spreading, longest branches 1.5-5 cm long, pedicels often longer than the 3-5 mm long spikelets; calluses glabrous; lemmas crisply puberulent on the keel and marginal veins, glabrous elsewhere, rarely glabrous throughout Poa pseudoabbreviata
11 Panicles contracted or open, if open and broadly rhomboidal to pyramidal, the branches not as above or, if approximately so, the calluses webbed or the lemma keels and marginal veins short- to long-villous. > 12
12 Sheaths closed from 1/10 – 1/4 (1/3) their length; panicles 1-7(10) cm long, contracted, branches shorter than 1.5 cm; plants densely tufted, basal branching all or mainly intravaginal; lower glumes usually 3-veined, lanceolate to broadly lanceolate, upper glumes subequal to or longer than the lowest lemmas; culms 1-25(30) cm tall; plants of high alpine and tundra habitats (sect. Abbreviatae). > 13
13 Lemmas short- to long-villous on the marginal veins and distal 3/4 of the keel, glabrous or softly puberulent between the veins; calluses webbed or glabrous Poa abbreviata
13 Lemmas glabrous or the keel and marginal veins sparsely puberulent proximally, glabrous between the veins; calluses glabrous. > 14
14 Anthers 0.2-0.8 mm long; spikelets 3-4 mm long; lower glumes usually exceeding the lower lemmas; upper florets frequently exceeded by or only slightly exceeding the glumes; blades thin, flat, folded, or slightly inrolled Poa lettermanii
14 Anthers 0.8-1.2 mm long; spikelets 3.5-7 mm long; lower glumes shorter than to equaling the lower lemmas; upper florets exceeding both glumes; blades moderately thick, often folded and inrolled on the margins. > 15
15 Adaxial surfaces of the innovation blades smooth or sparsely scabrous, long cells papillate (at 100x); upper culm blades with 7-15 closely spaced ribs on the adaxial surface; plants of California Poa keckii
15 Adaxial surfaces of the innovation blades densely and minutely hispidulous, puberulent, or scabrous, rarely smooth, long cells not papillate (at 100x); upper culm blades with 5-9 well-spaced ribs on the adaxial suface; plants of British Columbia, Washington, and Oregon Poa suksdorfii
12 Sheaths closed for 1/10 – 7/8 their length; panicles 1-40 cm long, loosely contracted to open, branches 0.5-20 cm long, or the panicles contracted to loosely contracted with the branches 0.5-2 cm long and the plants loosely tufted; basal branching mainly extravaginal or pseudointravaginal; lower glumes 1-3-veined, subulate to broadly lanceolate; upper glumes shorter than to subequal to the lowest lemmas; culms 5-150 cm tall; plants of various habitats. > 13
16 Sheaths closed for 1/10-1/5 their length; basal branching mainly extravaginal; lower 1-3 leaves of the culms and innovations bladeless; anthers 0.8-1.2 mm long, sometimes poorly developed. > 17
17 Flag leaf nodes at or above midculm length Poa nemoralis
17 Flag leaf nodes usually in the basal 1/3 of the culms. > 18
18 Anthers poorly developed, mature anther sacs about 0.1 mm wide and indehiscent; panicles dense to moderately dense, ovoid, 1.5-3.5 cm long; panicle branches not glaucous, angles smooth or sparsely scabrous; glumes broadly lanceolate, equal; upper glumes 3.7-4.7 mm long, the length 3.6-4.1 times the width; lemmas 3.7-4.5 mm long, glabrous between the veins, lateral veins usually glabrous, infrequently softly puberulent Poa laxa x glauca
18 Anthers well developed, mature anther sacs usually about 0.2 mm wide and dehiscent, rarely aborted; panicles dense to loose, ovoid to lanceoloid, 1-10 cm long; panicle branches glaucous, the angles scabrous, at least below the spikelets; glumes narrowly to broadly lanceolate, subequal; upper glumes 2-3.8(5.2) mm long, the length usually more than 4.1 times the width; lemmas 2.5-4 mm long, glabrous or softly puberulent between the veins, lateral veins usually sparsely softly, puberulent to short-villous Poa glauca
16 Sheaths closed for 1/5 – 7/8 their length; basal branching extravaginal, mixed extra- and intravaginal, or pseudointravaginal; culms and innovations with or without bladeless leaves; anthers 0.2-1.2 mm long, well developed. > 17
19 Calluses usually glabrous, rarely sparsely and shortly webbed; palea keels softly puberulent to short-villous for much of their length; lemmas puberulent between the veins; panicles (5)8-20 cm long, broadly pyramidal; panicle branches moderately to densely scabrous on the angles, longest branches 5-12 cm long, with 3-8 spikelets Poa autumnalis
19 Calluses webbed or glabrous, if glabrous then the palea keels glabrous, lemmas glabrous between the veins, panicles 2-8 cm long, usually loosely contracted, infrequently contracted, panicle branches smooth or sparsely scabrous, longest branches 1-3(4) cm long, with 1-8 spikelets. > 20
20 Panicles 2-8 cm long, usually loosely contracted, infrequently contracted; panicle branches usually ascending or weakly divergent, infrequently erect, smooth or sparsely scabrous, sulcate, longest branches 1-3(4) cm long; calluses webbed or glabrous; anthers (0.6)0.8-1.1(1.3) mm long; sheaths closed for 1/5-1/3 their length; plants alpine Poa laxa
20 Panicles 2.5-40 cm long, open; panicle branches loosely ascending, spreading, or reflexed, smooth or scabrous, angled, sulcate, or terete, longest branches usually longer than 3 cm; calluses webbed; anthers 0.2-1.2 mm long; sheaths closed for 1/4-3/4 their length; plants alpine or not. > 21
21 Panicle branches smooth or sparsely scabrous, usually terete or slightly sulcate; lower glumes subulate to broadly lanceolate; lemmas glabrous between the veins. > 22
22 Lower glumes subulate to narrowly lanceolate, keels usually scabrous; lemma keels short- to long-villous for 1/3-2/3 their length; lateral veins glabrous; lemma apices narrowly acute; spikelets lanceolate to narrowly lanceolate, green to purple; panicle branches sparsely scabrous, longest branches with (3)4-15 spikelets; palea keels evenly pectinate-ciliate or scabrous at midlength Poa leptocoma
22 Lower glumes narrowly to broadly lanceolate, keels usually smooth; lemma keels long-villous for 1/2 - 4/5 their length; lateral veins glabrous or hairy; lemma apices acute; spikelets lanceolate to ovate; panicle branches smooth or sparsely scabrous, if sparsely scabrous, with 1-3 ovate, dark purple spikelets on the lax to drooping capillary branches; longest branches with 1-18 spikelets; palea keels softly puberulent or scabrous at midlength. > 23
23 Longest panicle branches with (3)6-18 spikelets; palea keels scabrous or sparsely puberulent at midlength; lemmas usually sparsely puberulent on the lateral veins; lower branches usually reflexed Poa reflexa
23 Longest panicle branches with 1-3(5) spikelets; palea keels sparsely scabrous at midlength; lemmas glabrous on the lateral veins; lower branches usually laxly ascending to spreading Poa paucispicula
21 Panicle branches sparsely to densely scabrous, terete or angled; lower glumes subulate or broader; lemmas glabrous or puberulent between the veins. > 22
24 Panicles conical, the lower nodes with (2)3-10 branches; branches eventually reflexed; upper sheaths often ciliate on the overlapping margins near the point of fusion; intercostal regions of the lemmas usually sparsely puberulent, lateral veins at least sparsely puberulent; palea keels puberulent Poa sylvestris
24 Panicles not conical, the lower nodes with 1-7 branches; branches usually ascending to spreading, sometimes drooping or reflexed; upper sheaths not ciliate on the margins; lemmas glabrous or puberulent between the keel and marginal veins; palea keels puberulent or glabrous. > 25
25 Lemmas usually puberulent on the lateral veins and between the veins; lower cauline sheaths and ligules densely retrorsely scabrous; panicles (6)12-40 cm long, with 2-7 branches at the lower nodes; lower glumes 1-veined; plants densely tufted Poa occidentalis
25 Lemmas glabrous on the keel, lateral veins, and between the veins, rarely puberulent on the lateral veins and between the veins; sheaths and ligules smooth or sparsely to moderately densely retrorsely scabrous; panicles 3-30 cm long, branches 1-3(5) per node; lower glumes 1-3-veined; plants densely to loosely tufted. > 26
26 Plants loosely tufted or with solitary culms, long-rhizomatous; lower glumes lanceolate; palea keels scabrous; panicles 14-30 cm long Poa laxiflora
26 Plants densely to loosely tufted, sometimes shortly rhizomatous; lower glumes subulate to lanceolate; palea keels scabrous or puberulent; panicles 3-15(18) cm long. > 27
27 Ligules 1.5-4(6) mm long, obtuse to acute; lemmas often purple, keels pubescent for 1/3-2/3 their length, apices usually bronze-colored, sharply acute to acuminate; palea keels evenly pectinate-ciliate to scabrous; lower glumes 1-veined Poa leptocoma
27 Ligules 0.3-2.1 mm long, truncate; lemmas green, keels pubescent for 2/3 their length or more, apices white or faintly bronze, acute to obtuse; palea keels scabrous or puberulent; lower glumes 1-3-veined. > 28
28 Palea keels puberulent; anthers (0.5) 0.8-1.2 mm long; lemmas (2.5)3.2-4.7 mm long, lateral veins distinct Poa wolfii
28 Palea keels scabrous; anthers 0.2-0.8 mm long; lemmas 2.5-4 mm long, lateral veins faint Poa paludigena

Poa Subkey III

1 Calluses usually with a crown of hairs, hairs 1-2 mm long, sinuous; lemmas 4.5-7 mm long, 5-7-veined, outer margins usually with hairs to 0.2 mm long, marginal veins usually glabrous, sometimes long-villous; bases of the basal sheaths densely retrorsely strigose, hairs 0.1-0.2 mm long, thick; plants of subsaline boreal to low arctic coastal beaches and meadows (Poa subg. Arctopoa) Poa eminens
1 Calluses usually glabrous or webbed, sometimes with a crown of hairs; lemmas 2-8 mm long, 5(7)-veined, outer margins glabrous, marginal veins glabrous or not; bases of the basal sheaths glabrous; plants of various habitats. > 2
2 Culms and nodes strongly compressed; culms usually geniculate; lower culm nodes usually exserted; panicle branches angled, scabrous on the angles; sheaths closed for 1/10 – 1/5 their length Poa compressa
2 Culms terete to somewhat compressed, nodes not or only weakly compressed; culms geniculate or not; lower culm nodes exserted or not; panicle branches angled or terete, smooth or scabrous; sheath closure varied. > 3
3 Panicles 3-12(18) cm long, narrowly cylindrical or lobed, congested, usually with over 100 spikelets; plants unisexual; spikelets sexually dimorphic; pistillate plants: calluses webbed dorsally and below the marginal veins, lemmas 4.2-6.4 mm long, keels and marginal veins densely long-villous, panicle branches usually moderately to densely coarsely scabrous; staminate plants: calluses glabrous or sparsely webbed dorsally, rarely also webbed below the marginal veins, lemmas 3.5-5 mm long, keels and marginal veins glabrous or moderately densely and shortly pubescent, panicle branches sparsely to moderately scabrous; all plants: blades flat or folded, adaxial surfaces glabrous; plants native to the southern Great Plains, infrequently introduced elsewhere Poa arachnifera
3 Panicles 1-30 cm long, contracted to open, infrequently narrowly cylindrical or lobed and congested with over 100 spikelets; plants unisexual or bisexual; spikelets not sexually dimorphic; calluses glabrous, webbed, or with a crown of hairs, rarely with 3 webs; lemma keels and marginal veins glabrous or hairy; panicle branches smooth or scabrous; blades flat, folded, or involute, adaxial surfaces sometimes hairy in plants with contracted or loosely contracted panicles and unisexual spikelets; plants widespread. > 4
4 Basal branching extravaginal, branches initiated as pinkish to purplish, fleshy-scaled buds, the scales becoming brownish and flabelliform after shoot development; sheaths closed for at least 9/10 their length; florets unisexual Poa sierrae
4 Basal branching extra- or intravaginal or both, branches not initiated as persistent pinkish to purplish, fleshy-scaled buds; sheaths closed for at least 1/15 their length; florets bisexual or unisexual. > 5
5 Lemmas totally glabrous, often scabrous; calluses webbed or diffusely webbed, hairs at least (1)2 mm long. > 6
6 Panicles 10-20 cm long, open, pyramidal, sparse; sheaths closed for 1/15 - 1/5 their length; florets bisexual; plants of coastal redwood forests in northern California Poa kelloggii
6 Panicles 1-10.5 cm long, loosely contracted to open, lanceoloid to pyramidal, congested to sparse; sheaths closed for 1/3 – 9/10 their length; florets unisexual or bisexual; plants of the Pacific coast states and provinces. > 7
7 Lemmas 4-7 mm long, smooth or sparsely scabrous between the veins. > 8
8 Blades flat or folded, margins smooth, adaxial surfaces smooth or sparsely scabrous; blades of culm leaves gradually reduced in length upwards; collars smooth or sparsely scabrous Poa chambersii
8 Blades involute, margins scabrous, adaxial surfaces moderately to densely scabrous or pubescent, especially those of the innovations; blades of the culm leaves steeply reduced in length upwards, some collars usually sparsely hispidulous Poa piperi
7 Lemmas 2.5-5 mm long, moderately to densely scabrous between the veins. > 8
9 Lemmas 2.5-4(4.5) mm long; rachilla internodes 0.8-1.1 mm long; panicles 1-5(7) cm long, ovoid, loosely contracted, congested or moderately congested, branches erect to ascending, longest branches 0.5-3 cm; blades 0.5-1(1.5) mm wide Poa confinis
9 Lemmas (3.2)4.2-5 mm long; rachilla internodes 1-1.3 mm long; panicles (4) 5.5-10.5(12.5) cm long, ovoid to broadly pyramidal, open, or eventually loosely contracted, sparse, branches laxly ascending, longest branches 2.1-4.5 (7) cm; blades 1.5-2.4 mm wide Poa diaboli
5 Lemmas variously pubescent or glabrous; calluses glabrous or not, webbed or not, hairs long or short; florets never with both glabrous lemmas and long-webbed calluses. > 6
10 Plants 8-12(20) cm tall; panicles 2.5-5 cm long, erect, with 10-25(30) spikelets, branches smooth or sparsely scabrous; calluses glabrous; palea keels smooth, glabrous or softly puberulent to short-villous; glume keels smooth; leaf blades thin, flat, soft; plants stoloniferous Poa supina
10 Plants (5)10-150 cm tall; panicles 1-30(41) cm long, erect or lax, with 10-100+ spikelets, branches smooth or scabrous; calluses glabrous or with hairs; palea keels sometimes partially scabrous; glume keels smooth or scabrous; leaf blades various; plants stoloniferous or not. > 11
11 Lemma keels softly puberulent for 3/5 their length, hairs usually sparse, marginal veins glabrous or puberulent to 1/4 their length, intercostal regions smooth and glabrous; lateral veins prominent; calluses webbed; palea keels smooth, muriculate, tuberculate, or scabridulous; lower glumes 1-veined, usually arched to sickle-shaped; ligules 3-10 mm long, acute to acuminate; panicle branches angled, angles densely scabrous; plants usually weakly stoloniferous Poa trivialis
11 Lemmas glabrous or variously pubescent, if as above, the lateral veins faint or moderately prominent or the calluses glabrous or the palea keels distinctly scabrous or hairy or the lower glumes 3-veined; calluses glabrous or hairy; palea keels scabrous at least near the apices; lower glumes 1-3-veined, not arched, not sickle-shaped; ligules 0.5-18 mm long, truncate to acuminate; panicle branches terete or angled, smooth or scabrous; plants stoloniferous or not. > 12
12 Culm leaf blades steeply reduced in length upward, flag leaf blades absent or to 1(3) cm long, less than 79(75) the length of the sheath; calluses glabrous; lemmas usually villous on the keel and marginal veins, glabrous elsewhere, sometimes glabrous throughout; sheaths closed for about 73 their length; blades usually all involute and moderately firm, adaxial surfaces, at least those of the innovations, usually densely scabrous to puberulent; panicles contracted; spikelets laterally compressed; florets unisexual; plants of mountain slopes, never of low, wet ground Poa fendleriana
12 Culm leaf blades gradually reduced in length upward or the midculm blades longer than those below; flag leaf blades usually over (0.5)1 cm long, usually more than 1/7 the length of the sheath or, if as above, most or all blades flat and the panicles open or the sheaths closed for 1/10-1/5(1/4) their length and the blades folded and firm and the adaxial surfaces smooth or nearly so and the florets bisexual or the spikelet lengths 4-5 times the widths; calluses glabrous or with hairs; lemmas glabrous or variously pubescent; sheaths closed for 1/10-9/10 their length; blades as above or not; panicles contracted or open; spikelets laterally compressed or subterete; florets bisexual or unisexual; plants of various habitats, sometimes of low, wet ground. > 13
13 Calluses glabrous, diffusely webbed with hairs to 1/2 the lemma length, or with a crown of hairs, or sparsely and dorsally webbed with hairs to 1/4 the lemma length; lemmas glabrous or pubescent [for opposite lead, see p. 499]. > 14
14 Spikelets subterete to weakly laterally compressed, the lengths (3.8)4-5 times the widths; panicles usually contracted, sometimes open at anthesis; sheaths closed for 1/10 – 1/4 their length; calluses glabrous or with a crown of hairs; adaxial surfaces of the innovation blades glabrous, smooth or scabrous, not densely scabrous between the veins, flat and soon withering or folded and somewhat firm; florets bisexual Poa secunda
14 Spikelets laterally compressed, the lengths 2-3.5(3.8) times the widths; panicles contracted or open; sheaths closed for 1/10 – 9/10 their length; calluses glabrous, diffusely webbed, with a crown of hairs, or dorsally webbed with hairs to 1/4 the lemma length; adaxial surfaces of the innovation blades glabrous or with hairs, smooth or densely scabrous between the veins, flat and late withering, folded, soft and firm, or involute; florets bisexual or unisexual. > 15
15 Sheaths closed for 1/10 – 1/5(1/4) their length, smooth or sparsely scabrous, glabrous; panicles usually contracted, sometimes loosely contracted or open; paleas usually glabrous between the keels, if hairy, the panicles contracted; lemma keels, marginal veins, and, often, lateral veins short- to long-villous, intercostal regions usually glabrous, if hairy, the panicles contracted; lemma apices often blunt; calluses usually glabrous, occasionally dorsally webbed, hairs to 1/4 the lemma length; innovation blades usually folded and firm, infrequently flat and somewhat soft, adaxial surfaces glabrous, smooth or moderately scabrous, mainly over the veins; florets bisexual; plants usually of low, wet, somewhat alkaline or subsaline soils, from the valleys of the eastern foothills of the Rocky Mountains to the Great Plains, sometimes extending to timberline, rarely on slopes west of the continental divide Poa arida
15 Sheaths closed for 1/6 – 9/10 their length, smooth or retrorsely scabrous, glabrous or with hairs; panicles contracted or open; paleas glabrous or hairy between the keels; lemmas glabrous or variously hairy, apices blunt or pointed; calluses glabrous, shortly webbed, or diffusely webbed; innovation blades flat, folded, or involute, soft or firm, adaxial surfaces glabrous or hairy, smooth or densely scabrous between the veins; florets bisexual or unisexual; plants widespread but not of subalkaline or subsaline soils from the eastern slope of the Rocky Mountains to the Great Plains. > 16
16 Sheaths closed for 1/3-9/10 their length, sheaths of some leaves densely retrorsely scabrous or short-pubescent, at least on or near the collar margins; ligules of the lower culm leaves and innovations truncate, abaxial surfaces densely scabrous or softly puberulent; upper ligules 0.5-2 mm long; lemmas glabrous, or the keel and marginal veins softly puberulent to short-villous, intercostal region glabrous or hispidulous, infrequently softly puberulent; calluses usually glabrous, rarely shortly webbed. > 17
17 Sheaths hairy, hairs usually concentrated on and about the collars, collar margin hairs distinctly longer than those below the collar; sheaths closed for 2/3 – 9/10 their length; blades flat or a few folded, adaxial surfaces smooth or sparsely scabrous, particularly over the veins; florets bisexual and unisexual; plants from west of the Cascade divide Poa nervosa
17 Sheaths retrorsely scabrous or pubescent for 1/4 or more of the length below the collars, collar and sheath vestiture not differing in length; sheaths closed for 1/3 – 3/4 their length; blades of the innovations usually involute, adaxial surfaces usually densely scabrous to hispidulous on and between the veins; florets usually all pistillate, rarely bisexual or staminate; plants primarily from between the 100th meridian and the Cascade and Sierra Nevada mountains of western North America, rarely further west Poa wheeleri
16 Sheaths closed for (1/6)1/5 – 9/10 their length, glabrous, collars glabrous, smooth or infrequently moderately scabrous; ligules of the lower culm leaves and lateral shoots truncate to acuminate, smooth or scabrous abaxially, glabrous or softly puberulent; upper ligules 0.5-7 mm long; lemmas glabrous or variously pubescent; calluses glabrous, shortly webbed, or with a crown of hairs. > 17
18 Paleas pubescent between the keels; sheaths closed for (1/6)1/5 – 2/5 their length, smooth or slightly scabrous; lemma keels and marginal veins long-villous, intercostal regions usually short-villous, sometimes slightly softly puberulent on the lower back; panicles loosely contracted to open, branches smooth or sparsely scabrous; calluses glabrous or dorsally webbed; florets usually bisexual, anthers aborted late in development or 1.4-2.5 mm long; plants of subalpine to alpine and arctic habitats Poa arctica
18 Paleas glabrous between the keels; sheaths closed for 1/3 – 9/10 their length, smooth or scabrous; lemma keels and marginal veins glabrous or pubescent, intercostal regions usually glabrous, infrequently softly puberulent; panicles contracted to open, branches smooth or sparsely to densely scabrous or hispidulous; calluses glabrous, diffusely webbed or with a crown of hairs; florets bisexual or unisexual; pistillate florets with anthers 0.1-0.2 mm long; plants coastal to subalpine. > 19
19 Lemmas pubescent; calluses glabrous, diffusely webbed, or with a crown of hairs; blades involute, adaxial surfaces scabrous or pubescent, frequently densely so between the veins, or smooth and glabrous and the blades 0.5-1(1.5) mm wide; sheaths closed for 1/3-2/3 their length; plants of sand dunes and sandy soils along the Pacific coast. > 20
20 Lemmas 2.5-4(4.5) mm long; panicles fairly tightly to loosely contracted; culms 0.4-0.9 mm thick; blades 0.5-1(1.5) mm wide, thin to moderately thick, soft, mostly filiform, adaxial surfaces sparsely scabrous; calluses diffusely webbed Poa confinis
20 Lemmas 5-11 mm long; panicles tightly contracted; culms 1-2 mm thick; blades 1-4 mm wide, thick, moderately firm to firm; adaxial surfaces densely scabrous or hispidulous; calluses glabrous, diffusely webbed, or with a crown of hairs. > 21
21 Panicle rachises and culms beneath the panicles densely hispidulous; lemmas 5-7.5 mm long Poa douglasii
21 Panicle rachises and culms beneath the panicles glabrous, smooth or sparsely to moderately scabrous; lemmas (6)7.5-11 mm long Poa macrantha
19 Lemmas and calluses totally glabrous or, if the lemmas pubescent or the calluses dorsally webbed with hairs to 1/4 the lemma length, then the blades flat or folded, 2-5 mm wide, smooth or sparsely scabrous adaxially; sheaths closed for 1/4 - 9/10 their length; plants of inland regions, not growing in sand. > 20
22 Panicles 3-7 cm long, densely contracted, branches smooth or sparsely scabrous distally; spikelets 3.5-5.5 mm long, compact, rachilla internodes about 0.5 mm long; lemmas and calluses smooth, glabrous Poa atropurpurea
22 Panicles 2-22 cm long, densely contracted or open, if densely contracted, the branches sparsely to densely scabrous or spikelets 5.5-12 mm long; spikelets 3-12 mm long, looser, rachilla internodes 0.5-1.5 mm long; lemmas and calluses smooth or scabrous, glabrous or hairy. > 23
23 Basal branching nearly all intravaginal or mixed intra- and extravaginal; at least some innovation leaves with involute blades 0.5-2 mm wide and scabrous or pubescent on the adaxial surfaces; plants rarely rhizomatous, usually densely tufted; lemmas sparsely to densely scabrous, glabrous or sparsely softly puberulent near the base of the keels and/or marginal veins Poa cusickii
23 Basal branching all or mainly extravaginal; blades flat or folded, 2-5 mm wide, adaxial surfaces smooth or sparsely scabrous; plants shortly rhizomatous, loosely tufted or the culms solitary; lemmas smooth or sparsely scabrous, glabrous or the keel and marginal veins hairy, intercostal regions rarely pubescent. > 24
24 Panicles (5)12-22 cm, open, branches spreading to eventually reflexed; calluses glabrous Poa arnowiae
24 Panicles 2-9 cm long, tightly to loosely contracted, branches erect to ascending or scarcely spreading; calluses of some lemmas usually shortly webbed Poa chambersii
13 Calluses dor sally webbed, hairs over (1/3) 1/2 the length of the lemmas, sometimes with additional webs below the marginal veins; lemma short- to long-villous on the keels and marginal veins [for opposite lead, see p. 495]. > 14
25 Sheaths closed for 1/10 – 1/5 their length; spikelets 3-5 mm long; lemmas 2-3 mm long, glabrous between the keels and marginal veins; panicle branches angled, angles densely scabrous; plants sometimes stoloniferous, sometimes branching above the culm bases; florets bisexual Poa palustris
25 Sheaths closed for (1/6)1/5 – 9/10 their length; spikelets 3.5-12 mm long; lemmas 2-8 mm long, glabrous or hairy between the keels and marginal veins; panicle branches terete or angled, smooth or scabrous; plants rarely stoloniferous, usually rhizomatous, never branching above the culm bases; florets bisexual or unisexual. > 26
26 Sheaths closed for (2/5)1/2 – 9/10 their length, weakly to distinctly compressed, keels distinct, sometimes winged, wing to 0.5 mm wide, glabrous or the sides, collars, or throats pubescent; plants loosely tufted, shortly rhizomatous, never forming dense turf; culm blades flat or slightly folded, infrequently folded; innovations all or almost all extravaginal or a few intravaginal, with the intravaginal blades not involute and distinctly narrower than the culm blades; florets bisexual or unisexual, commonly some florets pistillate; anthers 0.1-0.2 mm or (1.3)2-4 mm long; plants mostly of forest openings and mountain thickets. > 27
27 Blades steeply reduced in length up the culms, flag leaf blades 0.2-3(6) long; panicles broadly pyramidal; usually at least some upper lemmas within the spikelets pubescent between the veins Poa cuspidata
27 Blades not steeply reduced in length up the culm, midculm blades sometimes longer than those below, flag leaf blades (1.4)3-20 cm long; panicles loosely contracted to narrowly pyramidal; lemmas glabrous or sparsely pubescent between the veins. > 28
28 Panicles erect, usually narrowly pyramidal, (8)13-29 cm long, proximal internodes usually longer than 4 cm; usually some lemmas within the spikelets pubescent between the veins Poa tracyi
28 Panicles nodding, ovoid, (2)4-10 cm long, proximal internodes 1.8-3 cm long; lemmas glabrous between the veins Poa rhizomata
26 Sheaths closed for (1/6)1/5 – 1/2(3/5) their length, terete to compressed, with or without distinct keels, usually glabrous, the sides infrequently retrorsely scabrous or pubescent; plants densely to loosely tufted or with solitary culms, sometimes forming dense turf; culm blades flat or folded; innovations all extravaginal or some intravaginal, blades of the intravaginal shoots sometimes involute and distinctly narrower than the culm blades; florets bisexual; anthers usually 1.2-2.5 mm long, sometimes some anthers aborting late in development and 1-1.5 mm long; plants widespread, sometimes of coastal belts and alpine and arctic habitats. > 27
29 Glumes subequal in length and width, usually nearly equaling the adjacent lemmas, distinctly keeled, keels scabrous; lower glumes (4)4.5-7 mm long; lemmas (4)5-8 mm long, the intercostal regions usually moderately to densely scabrous or hispidulous, infrequently softly puberulent to short-villous near the base and moderately to densely scabrous to hispidulous in the middle 73, rarely nearly smooth near the base and sparsely scabrous distally; intercostal regions of the paleas usually hispidulous, infrequently puberulent; blades (2)3-7 mm wide; culms usually stout, (20)30-120 cm tall; plants of coastal shores and low elevation wet meadows in Alaska and the low arctic Poa macrocalyx
29 Glumes unequal to subequal in length and width, distinctly shorter than to subequal to the adjacent lemmas, distinctly or weakly keeled, keels smooth or scabrous; lower glumes 1.5-5(6) mm long; lemmas 2-6(7) mm long, the intercostal regions smooth, glabrous or pilose to long-villous, and smooth or sparsely scabrous distally; intercostal regions of the paleas glabrous or pilose to short- villous; blades 0.4-6 mm wide; culms slender to stout, 10-70(100) cm tall; plants widespread. > 30
30 Palea keels usually pubescent, rarely nearly glabrous, intercostal regions usually at least sparsely and softly puberulent near the base, sometimes glabrous; glumes weakly to distinctly keeled, the keels smooth or sparsely to moderately scabrous; upper glumes usually subequal to the lower lemmas or slightly shorter; lemma intercostal regions and lateral veins pubescent near the base; ligules smooth or sparsely scabrous, usually rounded or obtuse to acute, infrequently truncate, entire or lacerate, not ciliolate; panicle branches (1)2-5 per node, usually smooth or sparsely scabrous, infrequently moderately scabrous Poa arctica
30 Palea keels glabrous or pubescent, intercostal regions glabrous, rarely sparsely hispidulous; glumes distinctly keeled, the keels usually sparsely to densely scabrous distally, infrequently smooth; upper glumes usually distinctly shorter than the lower lemmas; lemma intercostal regions glabrous, lateral veins glabrous or pubescent; ligules smooth or scabrous, usually truncate or rounded, infrequently obtuse to acute, entire, glabrous, or ciliolate; panicle branches (1)2-7(9) per node, smooth or sparsely to fairly densely scabrous. > 31
31 Intercostal surfaces of the lemmas visible, not or only partly concealed by hairs; lemma keels and marginal veins moderately to densely long-villous, more or less straight, lateral veins glabrous or softly puberulent, infrequently short-villous; panicle branches and ligules smooth or sparsely to fairly densely scabrous, longest branches 1-9 cm; plants widespread Poa pratensis
31 Intercostal surfaces of the lemmas concealed by the hairs over the keels and veins; lemma keels, marginal veins, and lateral veins copiously hairy, hairs of the keels and marginal veins cottony, those of the lateral veins somewhat shorter and sparser; panicle branches and ligules smooth or nearly so, longest branches 1-3 cm; plants of high arctic sands Poa sublanata

Poa Subkey IV

1 Calluses usually dorsally webbed, webs sometimes with 1 to few minute hairs, rarely the hairs somewhat diffuse [for opposite lead, see p. 503]. > 2
2 Lemma lateral veins pronounced, keels pubescent, marginal veins glabrous or softly puberulent at the base, lemmas glabrous elsewhere; lower glumes 1-veined, subulate to narrowly lanceolate, usually arched to sickle-shaped; callus web well developed Poa trivialis
2 Lemma lateral veins obscure to pronounced, keels glabrous throughout or, if pubescent, the marginal veins distinctly pubescent for more than 1/4 their length, lemma lateral veins and intercostal regions glabrous or pubescent, or, if pubescent as in P. trivialis, then the callus web short, scant, poorly developed and the lower glumes 3-veined and lanceolate or broader. > 3
3 Panicles open, conical, with whorls of (2)3-10, spreading to eventually reflexed, scabrous-angled branches at the lower nodes; lemmas hairy on the keel and veins, sometimes the intercostal regions also hairy; callus webs well developed Poa sylvestris
3 Panicles contracted to open, if open then not conical and without whorls of (2)3-10, eventually reflexed, scabrous-angled branches at the lower nodes; branches smooth or scabrous-angled; lemmas glabrous or hairy; calluses glabrous, with diffuse hairs, or with a scanty or well-developed web. > 4
4 Sheaths closed for (1/5)1/3-3/4 their length. > 5
5 Culms 8-35 cm tall, 0.5-0.8 mm thick; panicle branches smooth or sparsely scabrous; anthers to 1.3 mm long; plants alpine Poa laxa
5 Culms 23-120 cm tall, 0.5-2 mm thick; panicle branches smooth or scabrous; anthers to 1.8 mm long; plants of many habitats, including alpine habitats. > 6
6 Lemmas usually hairy on the keel and marginal veins, usually also on the intercostal regions; palea keels softly puberulent to short-villous at midlength; panicles open and erect, broadly pyramidal at maturity; callus webs sparse, poorly developed Poa autumnalis
6 Lemmas glabrous or with a few hairs at the base of the keel or marginal veins; palea keels scabrous, glabrous; panicles contracted to loosely contracted or open and lax; callus webs scant and short or well developed. > 7
7 Callus webs well developed; lemma keels glabrous; plants of eastern North America Poa saltuensis
7 Callus webs minute, sometimes somewhat diffuse; lemma keels glabrous or sparsely softly puberulent near the base; plants of western North America Poa cusickii
4 Sheaths closed for 1/20 – 1/4(1/3) their length. > 5
8 Basal branching all or mostly intravaginal; plants not stoloniferous. > 9
9 Culms 30-90 cm tall; panicles open; plants of the mountains in and around the Chihuahuan Desert Poa strictiramea
9 Culms 5-15(20) cm tall; panicles contracted; alpine plants of the Rocky Mountains Poa abbreviata
8 Basal branching all or mostly extra vaginal, or extra- and intravaginal and the plants stoloniferous. > 9
10 Flag leaf nodes usually in the lower 1/10-1/3 of the culms; flag leaf blades usually distinctly shorter than their sheaths; lemmas sometimes softly puberulent between the veins, lateral veins usually with at least a few minute hairs; ligules 1-4(5) mm long Poa glauca
10 Flag leaf nodes usually in the upper 2/3 of the culms; flag leaf blades shorter or longer than their sheaths; lemmas glabrous between the veins, lateral veins usually glabrous, rarely with 1 to several minute hairs; ligules 0.2-6 mm long. > 11
11 Spikelets narrowly lanceolate to lanceolate; glumes subulate to narrowly lanceolate, gradually tapering to narrowly acuminate apices; lower glume lengths 6.4-11 times the widths; ligules 0.2-0.5(1) mm long, truncate; flag leaf nodes at or above the middle of the culms; flag leaf blades usually longer than their sheaths; rachillas usually hairy, hairs to 0.15 mm long; webs usually short, scanty Poa nemoralis
11 Spikelets and glumes not as above or, if so, the ligules 1.5-6 mm long, truncate to acute, and the rachillas glabrous; flag leaf nodes at or above the lower 1/3 of the culm; flag leaf blades longer or shorter than their sheaths; webs short or long, scanty or not. > 12
12 Panicles (9)13-30(41) cm long, branches 4-15 cm long; culms closely spaced to isolated at the base; lower glumes tapering to the apices, lengths 6.4-10 times the widths; lemma keels abruptly inwardly arched beneath the scarious apices; lemma margins distinctly inrolled; rachillas usually muriculate, rarely sparsely hispidulous; web hairs usually longer than 2/3 the length of the lemmas Poa palustris
12 Panicles (1.5)3-15(17) cm long, branches 0.4-8(9) cm long; culms closely spaced at the base; lower glumes abruptly narrowing to the apices, lengths 4.5-6.3 times the widths; lemma keels not abruptly inwardly arched beneath the scarious apices; lemma margins not or slightly inrolled; rachillas usually muriculate or softly puberulent; web hairs shorter than 1/2(2/3) the length of the lemmas Poa interior
1 Callus glabrous or with a crown of hairs, hairs 0.1-2 mm long [for opposite lead, see p. 501]. > 2
13 Lemmas and calluses glabrous [for opposite lead, see p. 505]. > 14
14 Blades (4) 6-15 mm wide, flat or folded; sheaths closed for 1/2-1/4 their length, strongly compressed, keeled, keels winged Poa chaixii
14 Blades 0.5-5 mm wide, flat, folded, or involute; sheaths closed for 1/20-4/5 their length, not strongly compressed, if keeled, keels not winged. > 15
15 Sheaths closed for 2/5 – 4/5 their length; panicles 1-5(8) cm long, with (1)6-17(22) spikelets, nodes with 1-2 branches; branches appressed to spreading, smooth or sparsely scabrous; spikelets strongly compressed, lanceolate to broadly ovate; ligules hyaline, smooth, (1)2-4 mm long; blades 0.5-1 mm wide, thin, lax, filiform, soon withering; plants from the Columbia Plateau to southwestern Idaho and northwestern Nevada Poa leibergii
15 Sheaths closed for 1/20-3/4 their length, if for 2/5-3/4, then the panicles longer than 8 cm or with more than 20 spikelets or the ligules of the innovations (and sometimes also the culms) 0.5-2.5 mm long and scabrous and often milky white; blades (0.5)1-5 mm wide, sometimes moderately thick and firm and holding their form; plants of many regions, including the range of P. leibergii. > 16
16 Panicles (7)10-30 cm long, open, pyramidal, nodes with 2-5 moderately to densely scabrous branches; sheaths closed for 1/20 – 1/10 their length; basal branching intravaginal; plants of the Chisos Mountains of Texas to Mexico Poa strictiramea
16 Panicles 1-25 cm long, contracted to loosely contracted or, if open, nodes with 1-3(5) smooth or scabrous branches; sheaths closed for 1/20 – 3/4 their length; basal branching intravaginal, extravaginal, or both; plants of many regions, including the range of P. strictiramea. > 17
17 Sheaths closed for (1/4)1/3 - 3/4 their length; florets often unisexual, anthers 2-3.5 mm long or nonfunctional and to 1.8 mm long; uppermost ligules of the innovation leaves 0.2-0.5(2.5) mm long, scabrous, usually truncate; innovation blades usually involute; panicles contracted, loosely contracted, or open; lower glumes distinctly shorter than the lowest lemmas. > 18
18 Flag leaf blades usually absent or to 1 cm long; blades of the culm leaves sharply reduced in length upwards, similar in thickness and form to those of the innovations, moderately firm, usually involute; plants of southeastern Arizona and southwestern New Mexico Poa fendleriana
18 Flag leaf blades usually present and 1+ cm long; blades of the culm leaves not sharply reduced in length upwards, sometimes differing in thickness or form from those of the innovations, soft, narrow and withering or broader and flat; plants from other parts of the Flora region. > 19
19 Panicles contracted or loosely contracted, branches smooth or sparsely to densely scabrous; innovation blades 0.5-2 mm wide, abaxial surfaces smooth or scabrous, adaxial surfaces usually densely scabrous or hispidulous; plants from southern Yukon Territory to California and Colorado Poa cusickii
19 Panicles open or slightly contracted, branches smooth or sparsely scabrous; innovation blades 1-2 mm wide, abaxial surfaces smooth, adaxial surfaces usually smooth or sparsely scabrous; plants of Alaska, Yukon Territory, and Northwest Territories Poa porsildii
17 Sheaths closed for 1/20 – 2/5 their length; if sheaths closed for 1/4-2/5 their length then all florets bisexual, or the functional anthers 1.2-1.8 mm long, or the ligules of the uppermost innovation leaves 2+ mm long and smooth or scabrous, or the lower glumes subequal to the lowest lemmas; blades of the innovation leaves involute or not; panicles contracted; lower glumes shorter than to equaling the lowest lemmas. > 18
20 Culms 5-40 cm tall; panicles 3-7 cm long, densely contracted, nearly cylindrical; culm blades to 5 mm wide, often a bit fleshy and broader than those of the innovations, those of the innovations usually thin and soon withering, infrequently all blades flat and a bit fleshy; florets bisexual; plants of the Pacific coast Poa unilateralis
20 Culms 2-120 cm tall; panicles 1-25 cm long, densely to loosely contracted, not cylindrical; culm blades 0.5-5 mm wide and soft, culm and innovation blades not much differentiated or, if differentiated, then the basal blades moderately firm and involute; florets unisexual or bisexual; plants of non-coastal regions. > 21
21 Culms 30-120 cm tall; panicles (4)5-25 cm long; spikelet lengths 3-5 times the widths; plants of saline or non-saline habitats, often below the subalpine zone, if of non-saline habitats, the spikelet lengths (3.8)4-5 times the widths and the panicles usually over 10 cm long. > 22
22 Spikelets (4)7-10 mm long, subterete, narrowly lanceolate, lengths usually (3.8)4-5 times the widths; plants of many habitats, widespread Poa secunda
22 Spikelets 4.5-7 mm long, compressed, lengths 3-3.5 times the widths; plants of mineralized soils around hot springs in Napa County, California Poa napensis
21 Culms 2-40 cm tall; panicles 1-8 cm long; spikelet lengths 2-4 times the widths; plants of non-saline, subalpine or alpine habitats. > 22
23 Ligules of the innovations 2.5-6 mm long, hyaline, smooth; panicles loosely contracted or contracted; basal branching extravaginal; lower glumes distinctly shorter than the lowest lemmas; florets often unisexual Poa stebbinsii
23 Ligules of the innovations 0.5-2.5 mm long, usually milky, often scabrous; panicles contracted; some or all basal branching intravaginal; lower glumes distinctly shorter than or subequal to the lowest lemmas; florets bisexual or unisexual. > 24
24 Florets unisexual; anthers 2-4 mm long; blades involute Poa pringlei
24 Florets bisexual; anthers 0.6-3.5 long; blades flat, folded, or involute. > 25
25 Anthers 2.2-3.5 mm long; culms 15-40 cm tall; longest culm blades 1-3 cm long and fairly firm, with thick white margins and broadly prow-tipped apices, basal blades similar; plants of serpentine soils in Washington Poa curtifolia
25 Anthers 0.6-1.2(2) mm long; culms 2-25 cm tall; basal and upper culm leaves not always similar, culm leaves without the above combination of characteristics; plants of non-serpentine soils from British Columbia to California. > 26
26 Abaxial surfaces of the innovation blades smooth or sparsely scabrous, epidermes with papillae on the long cells (at l00x); abaxial surfaces of the flag leaf blades with 7-15 closely spaced ribs; culms 2-6(10) cm tall; plants of California Poa keckii
26 Abaxial surfaces of the innovation blades densely hispidulous, scabrous, or softly puberulent, rarely smooth and glabrous, lacking papillae on the long cells (at 100x); abaxial surfaces of the flag leaf blades with 5-9 well-spaced ribs; culms 7-25 cm tall; plants of British Columbia, Washington, and Oregon Poa suksdorfii
13 Lemmas with hairs; calluses glabrous or hairy [for opposite lead, see p. 503]. > 14
27 Sheaths closed for 1/2-3/4 their length; lemmas mostly glabrous, lower lemmas of some spikelets usually sparsely softly puberulent near the base of the keels and/or marginal veins, lemmas glabrous elsewhere; panicles 4-7 cm long, with 13-50 spikelets, branches smooth or sparsely scabrous; spikelets 7-10 mm long, strongly laterally compressed; florets pistillate; plants of subalpine to alpine habitats, from southern British Columbia to California Poa cusickii
27 Sheaths closed for 1/20 – 3/4 their length, if closed for 1/2 - 3/4 their length, the lemmas pilose between the veins or the panicle branches moderately to densely scabrous; lemmas variously pubescent, frequently pilose between the veins; panicles 1-30 cm long, with 9-100+ spikelets; branches smooth or sparsely to densely scabrous; spikelets 3-12 mm long, subterete to strongly laterally compressed; florets bisexual or unisexual; plants of various habitats, including subalpine to alpine habitats, widely distributed, including from British Columbia to California. > 28
28 Sheaths closed for 1/3-1/2 their length; panicles (5)8-20 cm, erect or lax, broadly pyramidal at maturity, open, lower axils sometimes sparsely hairy; panicle branches spreading to reflexed, angled, longest branches 5-12 cm long, with 3-8 spikelets in the distal 1/3-1/4; paleas pilose; florets bisexual; plants of eastern North American woods Poa autumnalis
28 Sheaths closed for 1/20 – 3/4 their length, if closed for 1/3 – 3/4 their length, then the panicles contracted or loosely contracted, or the branches smooth, or the longest branches shorter than 5 cm, or the paleas glabrous, or the spikelets unisexual; panicles 1-40 cm long, lower axils glabrous; panicle branches erect, ascending, or widely divergent, terete or angled; plants widely distributed, including eastern North American woods. > 29
29 Basal branching mainly extra vaginal, usually occurring late in the season; sheaths closed for 1/10 – 1/5 their length; blades usually flat, sometimes folded, thin, soft; panicle branches usually scabrous-angled; lemmas distinctly keeled; spikelets laterally compressed, lengths 2-3 times the widths. > 30
30 Lemmas glabrous on the lateral veins and intercostal regions; culms usually with 1-2(3) nodes exserted, uppermost node usually at or above the lower 1/3 of the culm Poa interior
30 Lemmas usually at least sparsely softly puberulent on the lateral veins, intercostal regions with similar hairs or glabrous; culms with 0-1 nodes exserted, uppermost node usually in the lower 1/10-1/3 of the culms Poa glauca
29 Basal branching intra- or extra vaginal or mixed, if mostly extravaginal, branching often occurring early in the season; sheaths closed for 1/20 – 3/4 their length; blades involute, flat, or folded, thin and soft to thick and firm; panicle branches terete or angled, smooth or scabrous; lemmas weakly to distinctly keeled; spikelets subterete or laterally compressed, lengths 1.5-5 times the widths. > 30
31 Spikelets ovate, rachilla internodes 0.5-0.8 mm; panicles 2-6(8) cm long, open or loosely contracted; branches terete, usually smooth or sparsely scabrous, rarely moderately densely scabrous, longest branches 1-3(4) cm; leaves mostly basal, blades 1-6(12) cm long, 2-4.5 mm wide, flat, soft; calluses glabrous; lemmas distinctly keeled, keels and marginal veins long- to short-villous, intercostal regions short-villous; paleas softly puberulent to short-villous at midlength; florets bisexual Poa alpina
31 Spikelets lanceolate to narrowly ovate, rachilla internodes 0.5-2 mm long; panicles 1-40 cm long, open or contracted; branches terete or angled, smooth or variously scabrous, longest branches 0.5-15 cm; leaves not as above; calluses glabrous or with a crown of hairs; lemmas weakly to distinctly keeled, variously hairy; paleas glabrous or softly puberulent; florets bisexual or unisexual. > 32
32 Panicles contracted; florets usually unisexual, rarely bisexual, commonly pistillate; blades usually involute. > 33
33 Sheaths closed for 1/7- 1/3 their length; lemmas weakly keeled; calluses usually with a crown of hairs around the base of the lemma; adaxial surfaces of the innovation blades smooth or somewhat scabrous; anthers late-aborted, 0.8-1.8 mm long; plants of the high arctic Poa hartzii
33 Sheaths closed for 1/4 - 3/4 their length; lemmas strongly keeled; calluses glabrous; adaxial surfaces of the innovation blades usually hispidulous to softly puberulent on and between the veins; anthers of pistillate plants rudimentary, 0.1-0.2 mm long; plants not arctic. > 34
34 Sheaths closed for about 1/3 their length; culm leaf blades sharply reduced in length upwards, the flag leaf blades absent or vestigial, commonly less than 1 cm long, always less than 1/5 the sheath length, when present usually firm, not withering; innovation blades usually 1-3 mm wide; lemmas short- to long-villous on the keel and marginal veins Poa fendleriana
34 Sheaths closed for 1/4 - 3/4 their length; culm leaf blades gradually reduced in length upward along the culm or some midculm blades longer than the lower culm blades, culm blades narrow, thin and withering; innovation blades usually 0.5-1(2) mm wide; lemmas usually softly puberulent, sometimes short-villous on the keel and marginal veins Poa xnematophylla
32 Panicles contracted or open; florets usually bisexual, if unisexual, the panicles open; blades flat, folded, or involute. > 33
35 Panicles open or loosely contracted at maturity, 5-30 cm long, spikelets not crowded. > 36
36 Spikelets laterally compressed, lengths usually 3-3.8 times the widths; lemmas distinctly keeled, intercostal regions glabrous or with hairs distinctly shorter than those over the keel and marginal veins. > 37
37 Lemmas 2.5-3.5 mm long, usually glabrous throughout, infrequently with keels and marginal veins softly puberulent to short- or long-villous and/or intercostal regions sparsely softly puberulent; blades usually involute, rarely flat, scabrous; calluses usually glabrous, rarely sparsely and shortly webbed; panicles (7)10-30 cm long; plants of the Chisos Mountains in Texas and northern Mexico Poa strictiramea
37 Lemmas 4-6 mm long, keels and marginal veins, sometimes also the lateral veins, short- to long-villous, intercostal regions glabrous or sparsely pilose or hispidulous near the bases; blades flat or folded, smooth or sparsely scabrous; calluses glabrous or with a crown of hairs, hairs 0.2-2 mm; panicles 5-18(25) cm long; plants of coastal Alaska, the Pacific Northwest, and Rocky Mountains Poa stenantha
36 Spikelets subterete, lengths usually (3.8)4-5 times the widths; lemmas weakly keeled, usually at least sparsely softly puberulent, infrequently short-villous, between the veins, the hairs usually about the same length as those of the keel and marginal veins. > 37
38 Ligules of the culm leaves usually 2-6 mm long, smooth or scabrous, truncate to acuminate; basal tuft of leaves narrow or loosely clumped; basal leaves reaching 2-20+ cm, blades filiform or to 3 mm wide; panicle branches capillary or stouter, smooth or scabrous; plants widespread, sometimes on serpentine soils, often in wet habitats Poa secunda
38 Ligules of the culm leaves 0.5-1.5(2.5) mm long, scabrous, apices truncate to obtuse (acute); basal tuft of leaves narrow, tightly clumped; basal leaves reaching 2-8(13) cm, basal blades filiform; panicle branches capillary, distinctly scabrous; plants of thin, early drying serpentine soils in the Sierra Nevada foothills of California Poa tenerrima
35 Panicles contracted at maturity, sometimes open during anthesis, 1-30 cm long, spikelets crowded or not. > 36
39 Plants 2-6(10) cm tall; panicles 1-4(6) cm long; cauline blades soft, folded, 1-3.5(4.5) cm long, upper cauline blades 0.9-1.8 mm wide, abaxial surfaces with 7-15 ribs; spikelets 3.5-6 mm long; calluses glabrous; lemmas glabrous or the keel and marginal veins sparsely softly puberulent near the base; plants of high alpine habitats in the Sierra Nevada and adjacent ranges Poa keckii
39 Plants 5-120 cm tall; panicles 2-30 cm long; leaves not as above in all respects; spikelets 3-10 mm long; lemmas nearly glabrous to copiously pubescent, if hairy, only so near the base on the keel and marginal veins, the hairs softly to crisply puberulent; calluses glabrous or with a crown of hairs; plants widespread. > 40
40 Plants 5-40 cm tall; panicles 3-7 cm long, usually densely contracted, rarely loosely contracted, nearly cylindrical; culm blades 2-5 mm wide, flat or folded; innovation blades usually 1-1.5 mm wide, involute, infrequently similar to the culm blades; anthers fully developed; plants of the Pacific coast Poa unilateralis
40 Plants 10-120 cm tall; panicles 2-30 cm long, densely to loosely contracted, not nearly cylindrical; culm and innovation blades similar, 1-5 mm wide; anthers sometimes aborted late in development; plants of the high arctic or interior habitats of western North America. > 41
41 Anthers usually sterile and to 1.5 mm long, infrequently well developed and 2-2.8 mm long; plants 10-33(45) cm tall; blades folded to involute, 1.5-3 mm wide, abaxial surfaces smooth or sparsely scabrous; spikelets lustrous; lemmas usually weakly keeled, more or less evenly and loosely short- to long-villous on the lower 1/3-1/2, hairs mostly longer than 0.5 mm; calluses usually with a crown of hairs to 2 mm long; panicle branches smooth or sparsely to moderately scabrous; plants of the high arctic Poa hartzii
41 Anthers well developed, 1.2-3.5 mm long; plants 10-120 cm tall; blades flat, folded, or involute, 0.5-5 mm wide, abaxial surfaces smooth or scabrous; spikelets lustrous or not; lemmas weakly keeled or not, if the intercostal regions hairy, the hairs distinctly shorter than those on the keels or, if the lemmas more or less evenly hairy, then the hairs usually shorter than 0.5 mm; calluses usually glabrous, infrequently with a crown of hairs to 2 mm long; panicle branches smooth or sparsely to densely scabrous; plants of the high arctic or western North America, if of the high arctic, the lemma hairs shorter than 0.3 mm. > 42
42 Lemmas usually evenly strigulose across the lower 1/3-1/2, hairs 0.1-0.2 mm long, rarely to 0.3 mm on the keel and marginal veins; blades soft, involute; culms 10-30 cm tall; panicles 3-6 cm long, longest branches 1-3(4) cm long, smooth or sparsely scabrous Poa ammophila
42 Lemmas variously hairy, if as above, the panicle branches usually scabrous and/or the blades flat and soon withering; culms (10)20-120 cm tall; panicles 2-30 cm long; branches 1-15 cm long, sparsely to densely scabrous. > 43
43 Culm blades 1-3 cm long, flat, (1)1.5-3 mm wide, with thick, white margins and broadly prow-shaped apices; panicles 4-8 cm long, narrowly lanceoloid; spikelets 7-9 mm long; plants of serpentine slopes in the Wenatchee Mountains of Washington Poa curtifolia
43 Culm blades longer or narrower than above, margins not thick and white, apices narrowly prow-shaped; panicles 2-30 cm long, narrowly lanceoloid to ovoid; spikelets (4)5-10 mm long; plants widespread. > 44
44 Spikelets subterete to weakly laterally compressed, (4)5-10 mm long, lengths 3.5-5 times the widths; rachilla internodes usually 1-2 mm long; lemmas usually weakly keeled, 3.5-6 mm long, nearly glabrous or hairy all over the basal 2/3; culms (10)15-120 cm tall; panicles 2-25(30) cm long Poa secunda
44 Spikelets laterally compressed, (4)4.5-7 mm long, lengths 3-3.5 times the widths; rachilla internodes usually shorter than 1 mm; lemmas distinctly keeled, 3-4 mm long, usually glabrous, keels and marginal veins rarely sparsely puberulent proximally; culms 30-100 cm tall; panicles 5-15 cm long Poa napensis
... more about "Poa"
Robert J. Soreng +
Ill. +, Ind. +, Conn. +, N.J. +, N.Y. +, Ga. +, Wash. +, Utah +, Alaska +, Colo. +, Idaho +, N.Mex. +, Nev. +, Maine +, N.H. +, Vt. +, Del. +, D.C +, Wis. +, Iowa +, Mont. +, Oreg. +, Wyo. +, Pacific Islands (Hawaii) +, Md. +, Mass. +, R.I. +, Fla. +, Calif. +, W.Va. +, Tex. +, La. +, N.C. +, N.Dak. +, Nebr. +, Tenn. +, Ala. +, Ark. +, Ariz. +, Kans. +, Ky. +, Mich. +, Minn. +, Mo. +, Miss. +, Ohio +, Okla. +, Pa. +, Puerto Rico +, S.C. +, S.Dak. +, Va. +, Alta. +, B.C. +, Greenland +, Man. +, N.B. +, Nfld. and Labr. +, N.S. +, N.W.T. +, Nunavut +, Ont. +, P.E.I. +, Que. +, Sask. +  and Yukon +
bowden1961a +, duckert-henroid1987a +, gillespie2005a +, gillespie2006a +, hiesey1982a +, hitchcock1951a +, hulten1942a +, kellogg1985a +, marsh1952a +, munz1959a +, soreng1985a +, soreng1991a +, soreng1991b +, soreng1993a +, soreng1998d +, soreng2003a +, soreng2005a +, tsvelev1976b +  and tutin1952a +
Gramineae +
Poaceae tribe Poeae +