Herbs, annual or perennial, unarmed. Stems prostrate to erect, glabrous or pubescent. Leaves alternate, odd-pinnate or palmate; stipules present, persistent, adnate to petiole; petiolate or sessile; leaflets 3–9, stipels absent, blade margins usually entire or toothed, rarely lobed, surfaces glabrous or pubescent. Inflorescences (1–)25–100+-flowered, racemes, umbelliform, spicate, or headlike, axillary or terminal; bracts present or absent, connate or distinct; bracteoles present or absent. Flowers papilionaceous; calyx actinomorphic or zygomorphic, tubular or campanulate, sometimes inflated in fruit, lobes 5; corolla white, cream, pink, red, purple, or yellow, glabrous; stamens 10, diadelphous; anthers basifixed; pistil linear to lanceolate, style glabrous or pubescent, stigma terminal. Fruits legumes, sessile or stipitate, cylindric or laterally compressed, lanceolate to elliptic, dehiscent, usually longitudinally, rarely transversely or indehiscent, included in marcescent corolla or slightly exserted, papery, membranous, or leathery, glabrous or pubescent. Seeds 1–4[–9], globose, ovoid-oblong, mitten-shaped, or reniform, hilum lateral. x = 5, 6, 7, 8.

Distribution

North America, Mexico, Central America, South America, Eurasia, Africa, Atlantic Islands, introduced in West Indies, Pacific Islands, Australia.

Discussion

Species ca. 280 (98 in the flora).

In the flora area, Trifolium is superficially similar to Medicago, Melilotus, and Trigonella. Trifolium differs from those genera by persistence of the corolla after anthesis, a legume that is included in or only slightly exserted from the persistent corolla, and distally dilated filaments (H. A. Gleason and A. Cronquist 1991; Wei Z. and M. A. Vincent 2010).

Trifolium has three major centers of diversity: the Mediterranean region of southern Europe, western Asia, and northern Africa; the California region in North America; and the eastern African highlands (M. Zohary and D. Heller 1984). In the New World, diversity is highest in the California region of the United States, the mountainous regions of western North America, and western South America. In North America, a suite of closely related species, centered in the southeastern United States, represents another locus of diversification.

Trifolium consists of subg. Chronosemium (Seringe) Reichenbach and subg. Trifolium; the latter is subdivided into eight sections (N. W. Ellison et al. 2006). Subgenus Chronosemium is represented in the flora area by the Old World species T. aureum, T. campestre, and T. dubium. All native New World species of subg. Trifolium represent a monophyletic lineage, sect. Involucrarium Hooker ex Lojacono. The introduced species of subg. Trifolium represent other sections: sect. Lupinaster (Fabricius) Seringe (T. lupinaster), sect. Trichocephalum W. D. J. Koch (T. subterraneum), sect. Trifoliastrum Gray (T. cernuum, T. glomeratum, T. nigrescens, T. repens, T. retusum, and T. suffocatum), sect. Trifolium (T. alexandrinum, T. angustifolium, T. arvense, T. echinatum, T. hirtum, T. incarnatum, T. lappaceum, T. medium, T. pratense, and T. striatum), and sect. Vesicastrum Seringe (T. fragiferum, T. hybridum, T. ornithopodioides, T. resupinatum, T. tomentosum, and T. vesiculosum). This differs dramatically from the phylogenetic arrangement of M. Zohary and D. Heller (1984), where the genus is subdivided into eight sections, and native New World species are placed in sects. Involucrarium and Lotoidea Crantz (in a narrow sense).

Species of Trifolium have been cultivated for centuries in parts of Europe as forage crops; some species were introduced into the flora area for that purpose. Of these, T. repens appears to have been the earliest introduction, perhaps as early as the mid 1600s (R. N. Mack 2003), and its spread across the continent was very rapid. Other commonly cultivated species include T. hirtum, T. hybridum, T. incarnatum, T. pratense, T. subterraneum, and T. vesiculosum; other species may also be cultivated in North America and may be important regionally (N. L. Taylor 1985; J. M. Gillett and Taylor 2001).

The following species have been mentioned as occurring in the flora area but are excluded as waifs or as only represented by cultivated material: Trifolium ambiguum M. Bieberstein, T. dalmaticum Visiani, T. gemellum Pourret ex Willdenow, T. maritimum Hudson, T. michelianum Savi, T. occidentale Coombe, T. pannonicum Jacquin, T. purpureum Loiseleur-Deslongchamps, T. rubens Linnaeus, T. scabrum Linnaeus, T. spumosum Linnaeus, T. squamosum Linnaeus, and T. stellatum Linnaeus.

Lojaconoa Bobrov 1967, which pertains here, is a later homonym of Lojaconoa Gandoger (Poaceae 1891).

Selected References

None.

Lower Taxa

Trifolium albopurpureum, Trifolium alexandrinum, Trifolium amoenum, Trifolium amphianthum, Trifolium andersonii, Trifolium andinum, Trifolium angustifolium, Trifolium appendiculatum, Trifolium arvense, Trifolium attenuatum, Trifolium aureum, Trifolium barbigerum, Trifolium barnebyi, Trifolium beckwithii, Trifolium bejariense, Trifolium bifidum, Trifolium bolanderi, Trifolium brandegeei, Trifolium breweri, Trifolium buckwestiorum, Trifolium calcaricum, Trifolium campestre, Trifolium carolinianum, Trifolium cernuum, Trifolium ciliolatum, Trifolium columbinum, Trifolium cyathiferum, Trifolium dasyphyllum, Trifolium dedeckerae, Trifolium depauperatum, Trifolium dichotomum, Trifolium douglasii, Trifolium dubium, Trifolium echinatum, Trifolium eriocephalum, Trifolium fragiferum, Trifolium friscanum, Trifolium fucatum, Trifolium glomeratum, Trifolium gracilentum, Trifolium grayi, Trifolium gymnocarpon, Trifolium haydenii, Trifolium hirtum, Trifolium howellii, Trifolium hybridum, Trifolium hydrophilum, Trifolium incarnatum, Trifolium jokerstii, Trifolium kentuckiense, Trifolium kingii, Trifolium lappaceum, Trifolium latifolium, Trifolium leibergii, Trifolium lemmonii, Trifolium longipes, Trifolium lupinaster, Trifolium macilentum, Trifolium macraei, Trifolium macrocephalum, Trifolium medium, Trifolium microcephalum, Trifolium microdon, Trifolium monanthum, Trifolium mucronatum, Trifolium nanum, Trifolium nigrescens, Trifolium obtusiflorum, Trifolium oliganthum, Trifolium ornithopodioides, Trifolium owyheense, Trifolium palmeri, Trifolium parryi, Trifolium pinetorum, Trifolium piorkowskii, Trifolium plumosum, Trifolium polyodon, Trifolium pratense, Trifolium productum, Trifolium reflexum, Trifolium repens, Trifolium resupinatum, Trifolium retusum, Trifolium rollinsii, Trifolium siskiyouense, Trifolium sonorense, Trifolium stoloniferum, Trifolium striatum, Trifolium subterraneum, Trifolium suffocatum, Trifolium thompsonii, Trifolium tomentosum, Trifolium trichocalyx, Trifolium variegatum, Trifolium vesiculosum, Trifolium virginicum, Trifolium willdenovii, Trifolium wormskioldii

Key

1	Involucres present, composed of free or fused bracts, surpassing pedicels; stipule margins usually dentate or lacerate, sometimes entire.	> 2
2	Herbs perennial.	> 3
3	Inflorescences 1–9-flowered; involucres incised nearly to base, lobes 2–8; keel petals usually purple-spotted.	Trifolium monanthum
3	Inflorescences (8–)10–50-flowered; involucres incised to 3/4, lobes 10–12; keel petals not spotted.	> 4
4	Calyx lobes subequal, abaxial rarely longer than tube; involucre: lobes sharply and acutely serrate; leaflet blades obovate to elliptic.	Trifolium wormskioldii
4	Calyx lobes ± equal, abaxial lobe longer than tube; involucre: lobes entire, irregular, bifurcate, or triaristate to lacerate; leaflet blades oblanceolate, obovate, linear, or elliptic.	> 5
5	Involucral lobes linear-lanceolate, entire; stipule margins entire; roots stout, branched, rhizomes absent.	Trifolium pinetorum
5	Involucre lobes triaristate to lacerate, or irregular to bifurcate; stipule margins entire, toothed, or lacerate; roots tuberous or taproots, rhizomes present or absent.	> 6
6	Roots tuberous, rhizomes present, elongate, slender; stipule margins entire or slightly lacerate; leaflet blades obovate, oblanceolate, or elliptic.	Trifolium siskiyouense
6	Roots taproots, slender, rhizomes absent or short; stipule margins toothed or lacerate; leaflet blades linear, elliptic, or obovate.	Trifolium mucronatum
2	Herbs annual or biennial.	> 7
7	Calyx and/or banner inflated in fruit.	> 8
8	Banner proximally inflated in fruit, distally twisted.	> 9
9	Calyx lobes: apex unbranched, setaceous; calyx longer than corolla.	Trifolium barbigerum
9	Calyx lobes: apex of at least some branched, flattened or setaceous; calyx equaling or shorter than corolla.	> 10
10	Abaxial and lateral calyx lobes conspicuously 2- or 3-fid, segments glabrous, sometimes flattened.	Trifolium cyathiferum
10	Calyx lobes unbranched or apex inconspicuously 3-fid, segments plumose, not flattened.	> 11
11	Corollas usually lavender or purple, sometimes purple with white tips; leaves and stems usually pubescent; seeds 1.6–2 mm.	Trifolium grayi
11	Corollas yellow; leaves and stems glabrous; seeds 3.1–3.4 mm.	Trifolium jokerstii
8	Banner inflated entire length in fruit, not distally twisted.	> 12
12	Flowers 10–27 mm; leaflet blades oblanceolate, obovate, orbiculate, or rhombic-obovate; involucral lobe apex acuminate, sometimes 2- or 3-fid or 3–5-fid.	> 13
13	Calyx tube 1.5–2.5 mm, abaxial lobe apex undivided or 2- or 3-fid; seed coat reticulate.	Trifolium fucatum
13	Calyx tube 2.5–4 mm, abaxial lobe apex 3–5-fid; seed coat smooth.	Trifolium piorkowskii
12	Flowers 3–11 mm; leaflet blades lanceolate, linear, obovate, or oblanceo­late; involucral lobe apex rounded to truncate, not split.	> 14
14	Involucres 3–13 mm, incised 1/2 their length; inflorescences 0.5–1 cm diam.; banners 4–7 mm; herbs 1–30 cm; stems erect or decumbent.	Trifolium depauperatum
14	Involucres 3–4 mm, lobes incised less than 1/2 their length; inflorescences 1–1.8 × 1.3–1.5 cm; banners 7–9 mm; herbs 15–55 cm; stems erect.	Trifolium hydrophilum
7	Neither calyx nor banner inflated in fruit.	> 15
15	Involucres flattened or cup- or bowl-shaped, when compressed laterally, nearly completely hiding calyces.	> 16
16	Involucral lobes entire or slightly toothed proximally; involucres conspic­uously villous; corollas ± equal to calyces.	Trifolium microcephalum
16	Involucral lobes conspicuously toothed; involucres glabrous or sparsely hairy; corollas longer than calyces.	> 17
17	Involucres flattened or shallowly bowl-shaped; inflorescences 0.5–0.8 cm; calyx lobes aristate, margins not membranous; early inflorescences hidden in stipules, subsessile, with 2–5 cleistogamous flowers.	Trifolium buckwestiorum
17	Involucres cup-shaped; inflorescences 0.8–1.7 cm; calyx lobes not or minutely aristate, margins membranous; early inflorescences not hidden, without cleistogamous flowers.	Trifolium microdon
15	Involucres rotate, bracts sometimes separate, or involucres flattened to bowl- or vase-shaped, when compressed laterally, not hiding flowers except proximally.	> 18
18	Calyx tubes slit between adaxial lobes, lobes shorter than or equal to tube, 3-fid or shouldered below subulate apex (usually entire in T. obtusiflorum); leaflet blades linear, oblong, lanceolate, oblanceolate, elliptic, rhombic, or obovate.	> 19
19	Flowers 11–16 mm; involucres 1–2 mm, incised 4/5–9/10 their length, lobes not lacerate; inflorescences 0.3–0.8 cm diam., 3–15-flowered.	Trifolium oliganthum
19	Flowers 12–20 mm; involucres 3–9 mm, incised 1/4–1/3 their length, lobes deeply lacerate; inflorescences 1–3 cm diam., 10–50-flowered.	> 20
20	Peduncles and calyces glabrous; calyx lobes usually 3-fid or shouldered; leaflet margins serrate.	Trifolium willdenovii
20	Peduncles and calyces glandular; calyx lobes usually entire, rarely 3-fid or shouldered; leaflet margins coarsely spinulose-serrate.	Trifolium obtusiflorum
18	Calyx tubes not slit between adaxial lobes, lobes longer than tube, usually entire and without shoulders, rarely 3-fid or laciniate; leaflet blades obo­vate to oblanceolate, or elliptic.	> 21
21	Calyces usually densely pubescent; involucres flattened or vase-shaped, 1–3 mm, incised 2/3–3/4 their length; seeds 3–6(–9).	Trifolium trichocalyx
21	Calyces glabrous; involucres flattened or bowl-shaped, 4–16 mm, incised 1/2 their length; seeds 1 or 2.	> 22
22	Calyx lobes 3-fid or laciniate; leaflet blades broadly elliptic to broadly obovate, apex rounded or truncate, often retuse; stems decumbent or ascending; Monterey Peninsula, California.	Trifolium polyodon
22	Calyx lobes entire (rarely with a small, lateral tooth); leaflet blades elliptic, obovate, or oblanceolate, apex acute or retuse; stems usually erect or ascending, rarely decumbent; w North America.	> 23
23	Banner petals 3.2–9.7 mm, included or exserted 0.1–5.7 mm beyond tips of calyx lobes, keel petals not beaked; mature seeds 1.1–1.6 mm; Alaska and British Columbia south to California, east to Arizona and Montana.	Trifolium variegatum
23	Banner petals 6.3–15.8 mm, exserted 1.5–8.4 mm beyond tips of calyx lobes, keel petals beaked or not; mature seeds 1.9–2.8 mm; California, s Oregon.	Trifolium appendiculatum
1	Involucres absent or vestigial, not exceeding pedicels, or if better developed, then formed of bracteoles, or with subtending leaves and stipules forming involucrelike structures; stipule margins usually entire, lobed, or toothed, sometimes serrate or denticulate.	> 24
24	Calyces and/or corollas inflated in fruit; legumes usually shorter than calyces.	> 25
25	Calyces not bilabiate in fruit, veins 5 or 20–36; involucres absent or vestigial.	> 26
26	Calyces inflated in fruit, corollas not inflated in fruit; tubes of fruiting calyces with interconnecting veins; involucres absent; bracteoles present, nearly equaling calyces; herbs 15–70 cm.	Trifolium vesiculosum
26	Calyces not inflated in fruit, corollas inflated in fruit; tubes of fruiting calyces without interconnecting veins; involucres vestigial, reduced to narrow ring; bracteoles absent; herbs 1–30 cm.	Trifolium depauperatum
25	Calyces markedly bilabiate in fruit, veins 5–10; involucres of bracteoles or a nar­row rim.	> 27
27	Herbs perennial; stems prostrate or creeping; flowers not resupinate; involucres of bracteoles cup-shaped, 3–6 mm.	Trifolium fragiferum
27	Herbs annual; stems prostrate, procumbent, ascending, or erect; flowers resupinate; involucres a narrow rim, 0.2 mm.	> 28
28	Inflorescences forming stellate-spreading clusters of calyces in fruit; calyces short-hairy or glabrescent in fruit, orifices open, lobes erect or divergent.	Trifolium resupinatum
28	Inflorescences not forming stellate-spreading clusters in fruit; calyces densely white-woolly, orifices abruptly constricted in fruit, adaxial lobes spreading or curved.	Trifolium tomentosum
24	Calyces and corollas not inflated in fruit; legumes longer than or equal to calyces.	> 29
29	Calyx lobes: abaxial lobes longer, adaxial very short; banner spatulate, boat-shaped, or obovate; legumes stipitate, seeds 1 or 2.	> 30
30	Terminal leaflets sessile; stipules 0.9–1.5 cm; banners: apex emarginate.	Trifolium aureum
30	Terminal leaflets obviously stalked; stipules 0.3–0.8 cm; banners: apex rounded or broadly acute.	> 31
31	Stipules 0.3–0.5 cm; flowers 2.8–3.5 mm; leaflet blades obovate to elliptic-lanceolate; corollas not or slightly ribbed.	Trifolium dubium
31	Stipules 0.5–0.8 cm; flowers 4.3–5 mm; leaflet blades rhombic to obovate; corollas obviously ribbed.	Trifolium campestre
29	Calyx lobes: abaxial ± equaling adaxial, or if lobes markedly unequal, then banner not spatulate or boat-shaped; legumes sessile or stipitate, seeds 1–9.	> 32
32	Inflorescences with 2–7 fertile flowers with corollas and 0–80 sterile flowers without corollas; inflorescences pedunculate, pushing into substrate in fruit, subterranean flowers chasmogamous.	Trifolium subterraneum
32	Inflorescences with 1–100+ fertile flowers with corollas; inflorescences not pushing into substrate in fruit, if so (T. amphianthum only), subterranean inflorescences sessile and subterranean flowers cleistogamous.	> 33
33	Pedicels 0–1 mm; bracteoles usually absent (present in T. arvense); calyx orifices thickened or closed by callosity or ring of hairs; legumes leathery distally, transversely dehiscent; seeds 1 or 2.	> 34
34	Calyx veins 20.	> 35
35	Calyces pilose; peduncles 0 cm; inflorescences appearing involucrate (involucrelike structures formed by enlarging stipules), disarticulating in fruit.	Trifolium hirtum
35	Calyces glabrous; peduncles 0.1–0.7 cm; inflorescences not involucrate, burlike, not disarticulating in fruit.	Trifolium lappaceum
34	Calyx veins 10–20 or not distinguishable.	> 36
36	Flowers 5–8 mm.	> 37
37	Leaflet blades broadly ovate or obovate to oblong, lengths 1–1.5(–2) times widths; calyx 3–4 mm.	Trifolium striatum
37	Leaflet blades elliptic, oblong, linear-oblong, linear-lanceolate, or obovate, lengths usually (2.5–)3–7 times widths; calyx 5–8 mm.	Trifolium arvense
36	Flowers 9–18 mm.	> 38
38	Herbs perennial.	> 39
39	Peduncles ± 0 mm, hidden by stipules of distal leaves; calyx tubes hairy; stipules broadly triangular, apex mucronate or setaceous.	Trifolium pratense
39	Peduncles 1–3 cm, not hidden by subtending stipules; calyx tubes glabrous; stipules lanceolate-linear, apex subulate.	Trifolium medium
38	Herbs usually annual, rarely biennial.	> 40
40	Leaflet blades broadly ovate or obovate to oblong, lengths 1–1.5(–2) times widths; corollas usually scarlet to red, rarely pink or white, banner oblong-elliptic, apex acute.	Trifolium incarnatum
40	Leaflet blades elliptic, oblong, linear-oblong, linear-lanceolate, or obovate, lengths usually (2.5–)3–7 times widths; corollas usually whitish, pale pink, or purple, banner narrowly-spatulate, oblong-spatulate, or ovate-elliptic, apex acute, obtuse, or notched.	> 41
41	Corollas shorter than or equaling calyx, usually pale pink or purple, rarely white; inflorescences 3–8 cm; calyx 8–13 mm, orifices closed by bilabiate callosities.	Trifolium angustifolium
41	Corollas longer than calyx, whitish; inflorescences 1–2.5 cm; calyx 6–8 mm, orifices open or closed by bilabiate callosities.	> 42
42	Calyx orifices closed by bilabiate callosities, lobes unequal, triangular-elliptic, stellate-spreading, tubes glabrescent; corollas 8–10 mm; banner apex acute; seeds 1.2–1.4 mm.	Trifolium echinatum
42	Calyx orifices open, hairy, lobes equal or abaxial 2 slightly longer, narrowly triangular, erect to slightly spreading, tubes appressed-hairy; corollas 13–16 mm; banner apex obtuse; seeds 2–2.2 mm.	Trifolium alexandrinum
33	Pedicels (0–)1–8(–12) mm; bracteoles usually present; calyx orifices open; legumes not leathery distally, longitudinally dehiscent; seeds 1–9.	> 43
43	Calyces glabrous.	> 44
44	Herbs perennial; stems creeping, rooting at nodes; peduncles erect, from prostrate stems; pedicels strongly reflexed in fruit; corollas equaling or 2 times calyces.	Trifolium repens
44	Herbs annual or perennial; stems usually erect or ascending, rarely prostrate, not rooting at nodes; peduncles erect or not, from prostrate or upright stems; pedicels reflexed or not; corollas shorter to longer than calyces.	> 45
45	Corollas 2+ times calyces.	> 46
46	Pedicels erect or slightly reflexed, sometimes only those of proximal flow­ers reflexed.	> 47
47	Calyx lobes curved or twisted.	> 48
48	Herbs annual; stems procumbent, decumbent, or ascending; inflo­rescences 0.8–1 cm diam.; peduncles 0–0.1 cm.	Trifolium glomeratum
48	Herbs perennial; stems erect; inflorescences 2–3.5 cm diam.; peduncles 3–12 cm.	Trifolium douglasii
47	Calyx lobes straight.	> 49
49	Herbs 4–10 cm; stems mat-forming, cespitose; flowers 1–4; brac­teoles membranous, connate, forming cuplike involucres.	Trifolium nanum
49	Herbs 10–20 cm; stems erect or ascending, loosely cespitose or rhizomatous; flowers 15–20; bracteoles purplish, scarious, some­times connate, forming involucres.	Trifolium parryi
46	Pedicels strongly reflexed.	> 50
50	Inflorescences: rachises not prolonged beyond flowers, without sterile flowers.	Trifolium hybridum
50	Inflorescences: rachises prolonged beyond (fertile) flowers, often bear­ing a cluster of sterile flower buds distally.	> 51
51	Stems 30–100 cm, fistulose; leaflet blades 2.3–5 cm wide.	Trifolium howellii
51	Stems 5–50 cm, not fistulose; leaflet blades 0.1–2 cm wide.	> 52
52	Calyx veins 5.	> 53
53	Peduncles thick, straight; banners straight, obovate to broadly elliptic.	Trifolium beckwithii
53	Peduncles slender, bent distally just below flowers; ban­ners curved, oblanceolate.	Trifolium bolanderi
52	Calyx veins 10 (5 sometimes faint).	> 54
54	Stems ± erect, loosely cespitose; leaves basal and cauline.	> 55
55	Leaflet blades lanceolate or elliptic; calyces 3–3.5 mm.	Trifolium productum
55	Leaflet blades lanceolate to linear; calyces 6–8.5 mm.	Trifolium dedeckerae
54	Stems ascending, cespitose; leaves mostly basal.	> 56
56	Inflorescences globose or subglobose; peduncles straight proximal to flowers; corollas salmon, buff-pink, or pink, with white or cream tips; calyx lobes equaling tubes.	Trifolium haydenii
56	Inflorescences hemispheric; peduncles curved distally, just below flowers, inflorescences appearing turned to one side; corollas purple, often white-tipped; calyx lobes shorter than tubes.	Trifolium rollinsii
45	Corollas less than 2 times calyces.	> 57
57	Pedicels straight or slightly reflexed in fruit.	> 58
58	Inflorescences loose, flowers 1–5, not overtopped by leafy stipules; calyx lobes straight in fruit.	Trifolium ornithopodioides
58	Inflorescences dense, flowers 10–20, overtopped by broad, membranous stipules; calyx lobes curved in fruit.	Trifolium suffocatum
57	Pedicels strongly reflexed or recurved in fruit.	> 59
59	Calyx lobes recurved in fruit.	> 60
60	Peduncles equaling or shorter than subtending leaves; stipule apex stramineous; corollas shorter than calyces.	Trifolium retusum
60	Peduncles longer than subtending leaves; stipule apex dark purple or reddish; corollas longer than calyces.	Trifolium nigrescens
59	Calyx lobes not recurved (except T. nigrescens) in fruit.	> 61
61	Calyx lobe margins hyaline, dentate or pectinate, markedly ciliate.	Trifolium ciliolatum
61	Calyx lobe margins green, purple, or pink, not dentate or pectinate, not ciliate.	> 62
62	Leaflet blades narrowly obcordate, obovate, oblanceolate, or linear, apex, at least some, retuse to deeply 2-fid.	Trifolium bifidum
62	Leaflet blades narrowly elliptic, lanceolate, obovate, obcordate, ovate, oblong, rhombic, or broadly elliptic, apex not 2-fid, sometimes shallowly retuse.	> 63
63	Leaflet blades narrowly elliptic or lanceolate, apex acute; calyx lobe margins membranous.	Trifolium palmeri
63	Leaflet blades obovate to obcordate or ovate, oblong, or rhombic, apex broadly rounded, broadly acute, truncate, emarginate, or retuse; calyx lobe margins not membranous.	> 64
64	Peduncles 0.6–1.5 cm, distal ones shorter; flowers 4–5.5 mm; banners: apex deeply emarginate.	Trifolium cernuum
64	Peduncles 1–9 cm; flowers 5–15 mm; banners: apex rounded, retuse, apiculate, erose-denticulate, or acute.	> 65
65	Calyx lobes (at least most) equaling to less than 2 times tube; stipule apex subulate, sharply recurved, dark purple or reddish.	Trifolium nigrescens
65	Calyx lobes 2 times tube; stipule apex acute or acuminate, usually erect, green.	> 66
66	Inflorescences 0.5–2 cm diam.; calyx lobes unequal, long-triangular; stipules ovate-lanceolate, membranous; corollas 5–8 mm; bracteoles cuplike.	Trifolium gracilentum
66	Inflorescences 2–4 cm diam.; calyx lobes equal, narrowly triangular to subulate; stipules broadly ovate, foliaceous; corollas 9–14 mm; bracteoles broad-obovate, truncate to 2-fid.	Trifolium reflexum
43	Calyces entirely or partly pubescent.	> 67
67	Inflorescences 4–30(–50)-flowered.	> 68
68	Pedicels erect or only those of proximal flowers reflexed in fruit.	> 69
69	Peduncles ± 0 cm, inflorescences largely hidden by broad, membranous stipules; herbs 3–10 cm; pedicels 0.1 mm.	Trifolium suffocatum
69	Peduncles (0–)1–17 cm, usually not hidden by stipules (partially hidden in T. macraei); herbs 0.8–30 cm; pedicels (0–)0.5–4 mm.	> 70
70	Leaflets 3 or 5(–9); stipule margins entire, irregularly dentate, or serrate.	> 71
71	Stipule margins finely and sharply serrate; stems erect, unbranched or branched distally; Alaska.	Trifolium lupinaster
71	Stipule margins entire or irregularly dentate; stems cespitose, numer­ous, short, branched from woody crown; Oregon to Montana, south­ward to California and New Mexico.	Trifolium gymnocarpon
70	Leaflets 3; stipule margins entire.	> 72
72	Inflorescences usually in pairs, partially hidden by terminal leaves and stipules; peduncles 0–0.2 cm; pedicels 0 mm.	Trifolium macraei
72	Inflorescences single, not hidden by terminal leaves and stipules; peduncles 1–17 cm; pedicels 0.5–3.5 mm.	> 73
73	Herbs canescent; leaflet blades oblanceolate to obovate, often folded, surfaces densely silvery-hairy; bracteoles absent; banners 8–10 mm, oblong, apex acute.	Trifolium friscanum
73	Herbs glabrous or pubescent, not canescent; leaflet blades oblong-elliptic, oblanceolate, or obovate, sometimes folded, surfaces gla­brous or hairy; bracteoles linear-lanceolate; banners 11–15 mm, broadly elliptic-ovate, apex rounded, apiculate.	Trifolium dasyphyllum
68	Pedicels curved or reflexed in fruit.	> 74
74	Peduncles ± geniculate distally.	> 75
75	Calyx tubular, lobes subequal, subulate.	Trifolium breweri
75	Calyx campanulate, bilabiate, lobes markedly unequal, adaxial longer than abaxial, foliaceous.	> 76
76	Calyx lobes, except abaxial, obovate, veins reticulate, surfaces gla­brous, sparsely pilose marginally.	Trifolium bejariense
76	Calyx lobes broadly triangular, veins slightly branched, surfaces villous.	Trifolium carolinianum
74	Peduncles straight.	> 77
77	Stems creeping, rooting at nodes; inflorescences 2 kinds, one aerial, long-pedunculate, flowers chasmogamous, other subterranean, flowers cleistogamous.	Trifolium amphianthum
77	Stems not creeping, not rooting at nodes; inflorescences aerial, flowers chasmogamous.	> 78
78	Herbs annual or biennial; stems not cespitose.	> 79
79	Calyx lobe margins dentate or pectinate, ciliate.	Trifolium ciliolatum
79	Calyx lobe margins entire.	> 80
80	Leaflet blades narrowly obcordate, obovate, oblanceolate, or linear, at least some with apex retuse to deeply 2-fid; flowers 6–8 mm; banners elliptic to oblong, apex rounded, apiculate.	Trifolium bifidum
80	Leaflet blades ovate, obovate, oblong, rhombic, or orbiculate, apex acute, rounded, emarginate, or obcordate; flowers 9–15 mm; banners obovate-oblong or ovate-oblong, apex usually rounded or retuse, sometimes erose-denticulate.	> 81
81	Stems erect or ascending; distalmost petioles 0.3–3.5 cm; calyx lobes 3–7 mm.	Trifolium reflexum
81	Stems decumbent; distalmost petioles 6–8 cm; calyx lobes 2–3.7 mm.	Trifolium kentuckiense
78	Herbs perennial; stems mostly cespitose.	> 82
82	Inflorescence rachises not surpassing distalmost flowers.	> 83
83	Herbs pubescent, 5–30 cm; stems erect or ascending; stipules 1.8–2 cm; leaflet blades 1.5–6 cm, margins entire; flowers 15–22 mm; corollas red-purple.	Trifolium attenuatum
83	Herbs mostly glabrous, 3–5 cm; stems densely matted; stipules 0.5–1 cm; leaflet blades 0.3–1.6 cm, margins sharply antrorsely serrate; flowers 8–13 mm; corollas creamy white.	Trifolium barnebyi
82	Inflorescence rachises surpassing distalmost flowers.	> 84
84	Calyx 7–10 mm, lobes narrowly triangular, acuminate, length less than 2 times tube; corollas 15–18 mm; leaflet margins entire.	Trifolium brandegeei
84	Calyx 3.3–15 mm, lobes narrowly triangular, linear, or subulate, length 2+ times tube; corollas 5.3–20 mm; leaflet margins entire, serrate, or serrulate.	> 85
85	Stems prostrate; stipule margins entire or finely serrulate; leaflet blades obovate to obcordate, largest to 1.6 × 1.2 cm; bracteoles linear-triangular, 0.5 mm; flowers 5.7–6.7 mm; banners obovate, apex broadly rounded or broadly acute.	Trifolium sonorense
85	Stems ascending; stipule margins entire proximally, 1–3-toothed distally; leaflet blades obovate or elliptic, largest to 4.2 × 2.5 cm; bracteoles scalelike, to 0.3 mm; flowers 13–17 mm; banners elliptic, apex tapered, sometimes retuse.	Trifolium latifolium
67	Inflorescences (5–)10–50(–80)-flowered.	> 86
86	Petioles 0.5–0.7 cm; stipules adnate to petioles, sheathing; leaflets (3–)5(–9).	Trifolium lupinaster
86	Petioles (0.3–)1–20(–25) cm; stipules not adnate to petioles, not sheathing; leaf-lets 3 or 5–9.	> 87
87	Leaflets 5–9.	> 88
88	Inflorescences 2.5–8 × 3–7 cm; calyx lobes 2–4 times tube.	> 89
89	Leaflets 5–7, blades linear, linear-lanceolate, or linear-elliptic, 2–7 cm; inflorescences 3–5 × 3–4 cm; calyx lobes slightly pilose; corollas rose-pink to purple.	Trifolium thompsonii
89	Leaflets (5–)7–9, blades broadly to narrowly obovate, 1–2.7 cm; inflo­rescences 2.5–8 × 3–7 cm; calyx lobes plumose; corolla white, creamy white, or pinkish, keel petals deep pink.	Trifolium macrocephalum
88	Inflorescences 1–3 × 1–3 cm; calyx lobes shorter than or to 1.5 times tube.	> 90
90	Pedicels 0 mm; calyces 9–11 mm; leaflet margins entire; seeds 1.6–2 mm.	Trifolium andersonii
90	Pedicels 1–4 mm; calyces 3–7.5 mm; leaflet margins dentate; seeds 2.5–4.5 mm.	> 91
91	Flowers 6–15, 7.5–13 mm; peduncles 1–6.5 cm, ± surpassing leaves, not bent distally; inflorescences 1–2 cm.	Trifolium gymnocarpon
91	Flowers 15–30, 11–13 mm; peduncles 5–15 cm, surpassing leaves, sharply bent distally, just below flowers; inflorescences 2–3 cm.	Trifolium lemmonii
87	Leaflets 3.	> 92
92	Pedicels absent or not all reflexed in fruit.	> 93
93	Leaflet blade lengths 3+ times widths.	> 94
94	Bracteoles conspicuous, 2–6 mm, proximal ones sometimes connate, forming involucre; banners broadly elliptic-ovate, folded distally, apex rounded, api­culate; ovaries pubescent distally.	Trifolium dasyphyllum
94	Bracteoles inconspicuous, 0–0.5 mm, not forming involucre; banners oblong or ovate to oblanceolate, apex usually acute or obtuse, rarely rounded or truncate; ovaries glabrous or pubescent distally.	> 95
95	Calyx veins 15–20; ovaries glabrous or pubescent distally.	> 96
96	Leaflet blades often folded, falcate; inflorescences spicate, ovoid to cylindric; calyx lobes subulate, straight.	Trifolium plumosum
96	Leaflet blades flat, not falcate; inflorescences umbellate, globose to ovoid; calyx lobes triangular or subulate, lateral and adaxial tortuous, curved downwards and inwards around corollas, abaxial straight.	Trifolium douglasii
95	Calyx veins 5–10; ovaries pubescent distally.	> 97
97	Peduncles 0.1–1 cm; inflorescences usually formed of 2 sessile heads, subtended by distal stipules and leaves, forming involucrelike structure, or involucre absent; stipules oblanceolate, margins entire; calyx rough-hairy or glabrous, lobes subequal.	Trifolium andinum
97	Peduncles 1–30 cm; inflorescences: distal stipules not forming involucrelike structure; stipules ovate to lanceolate, margins usually entire, sometimes slightly serrate proximally; calyx hairy or glabrous, lobes unequal.	Trifolium longipes
93	Leaflet blade lengths to 2 times widths.	> 98
98	Herbs perennial; stems erect or spreading, cespitose, little branched distally.	> 99
99	Stipules fused at base, broadly obovate, margins slightly lobed; leaflets slightly overlapping, blades ovate, obovate, or orbiculate, apex emarginate.	Trifolium owyheense
99	Stipules distinct at base, ovate to lanceolate, margins usually entire, sometimes slightly serrate proximally; leaflets not overlapping, blades linear, lanceolate to elliptic, or oblong, cauline sometimes ovate, apex acute.	Trifolium longipes
98	Herbs annual; stems erect, ascending, or prostrate, not cespitose, branched throughout or unbranched.	> 100
100	Peduncles 0–0.2 cm; inflorescences usually paired, sometimes one head slightly stalked, partially hidden by terminal leaves and stipules.	Trifolium macraei
100	Peduncles 0.5–15 cm; inflorescences single, not hidden by terminal leaves or stipules.	> 101
101	Calyces campanulate, veins 10 (additional faint veins sometimes present), sinuses rounded, lobes divergent; corollas shorter than calyces.	Trifolium albopurpureum
101	Calyces tubular, veins 20–30, sinuses acute, lobes not divergent, appearing rigidly erect; corollas shorter or longer than calyces.	> 102
102	Corollas shorter than calyces or absent.	Trifolium columbinum
102	Corollas longer than calyces.	> 103
103	Inflorescences bluntly conic, ellipsoid, globose, or sub­globose, 1.5–3 × 1.5–2.5 cm; leaflet blades broadly obovate or elliptic, 1.7–3.3 × 1.1–2 cm; corollas 12–16 mm; calyces 9–12 mm.	Trifolium amoenum
103	Inflorescences ovoid-ellipsoid, 1.1–2.2 × 1–1.5 cm; leaf­let blades obovate or oblanceolate, 0.5–1.5 × 0.2–1.1 cm; corollas 7–12 mm; calyces 4–8 mm.	Trifolium dichotomum
92	Pedicels reflexed in fruit.	> 104
104	Herbs perennial; stems creeping, rooting at nodes.	> 105
105	Inflorescences of 2 kinds: one terminal, aerial, long-pedunculate, flowers chas­mogamous, the other basal, subterranean, flowers cleistogamous.	Trifolium amphianthum
105	Inflorescences all aerial, flowers chasmogamous.	> 106
106	Peduncles 2–7 cm, single or paired at tips of erect stems, subtended by pair of opposite or subopposite, short-petiolate leaves; inflorescences 2–3.5 × 2–3.5 cm; flowers 15–30; leaflet blades broadly ovate or obcordate.	Trifolium stoloniferum
106	Peduncles 10–12 cm, single, arising from stolons; inflorescences 1.8–2.2 × 1.8–2.2 cm; flowers 25–50; leaflet blades obovate, rhombic, or elliptic.	Trifolium calcaricum
104	Herbs annual, biennial, or perennial; stems not creeping, not rooting at nodes.	> 107
107	Leaflet lengths 3+ times widths.	> 108
108	Herbs annual; leaflet blades narrowly obcordate, obovate, oblanceolate, or linear, apex rounded or truncate, shallowly to deeply retuse or deeply 2-fid.	Trifolium bifidum
108	Herbs perennial; leaflet blades elliptic, linear-elliptic, lanceolate, oblong, ovate, or linear, apex not deeply retuse to 2-fid.	> 109
109	Peduncles bent or curved proximal to flowers, inflorescences inverted or horizontal.	> 110
110	Ovaries pubescent distally; calyx curved in fruit, lobes unequal, lengths 2–3 times tube, plumose.	Trifolium eriocephalum
110	Ovaries glabrous; calyx straight, lobes equal, lengths 1–1.5 times tube, sparsely pubescent or glabrate.	Trifolium kingii
109	Peduncles straight, inflorescences erect.	> 111
111	Banners ovate to oblanceolate, apex tapering, acuminate or beaked.	Trifolium longipes
111	Banners broadly oblong-elliptic or obovate-oblong, apex rounded, acute, or retuse, sometimes mucronate or apiculate.	> 112
112	Leaflet blade apex narrowly acute or acuminate, margins entire; proximal bracteoles forming involucres; flowers 10–20; calyces 8–15 mm; w United States.	Trifolium attenuatum
112	Leaflet blade apex truncate to acute, margins entire or serrulate; bracteoles not forming involucres; flowers 20–40; calyces 4–7 mm; e United States.	Trifolium virginicum
107	Leaflet lengths usually to 2 times widths.	> 113
113	Herbs annual or biennial.	> 114
114	Calyces markedly bilabiate, lobes markedly unequal (adaxial longer than abaxial), oblong-ovate or broadly triangular, veins reticulate or branched.	> 115
115	Calyx lobes, except abaxial, obovate, pubescent along margins, veins reticulate.	Trifolium bejariense
115	Calyx lobes broadly triangular, lanceolate, or linear, uniformly villous, veins slightly branched.	Trifolium carolinianum
114	Calyces not markedly bilabiate, lobes ± equal, triangular, lanceolate or linear, or subulate, veins unbranched.	> 116
116	Inflorescence rachises not surpassing flowers; stipule apex recurved, dark purple or reddish; calyx lobes recurved in fruit.	Trifolium nigrescens
116	Inflorescence rachises sometimes surpassing flowers; stipule apex straight, green; calyx lobes straight in fruit.	> 117
117	Calyx lobes unequal, margins dentate or pectinate, strongly ciliate, sinuses narrow; inflorescences 0.5–2 cm diam.; seeds 2.5–3 mm.	Trifolium ciliolatum
117	Calyx lobes equal, margins entire, sinuses broad; inflorescences 2–4 cm diam.; seeds 1.2–1.5 mm.	Trifolium reflexum
113	Herbs perennial.	> 118
118	Herbs canescent; margins of stipules and leaflets coarsely spinulose-dentate.	Trifolium leibergii
118	Herbs glabrous or pubescent, not canescent; margins of stipules and leaves entire or toothed, not spinulose.	> 119
119	Inflorescence rachises not surpassing flowers; banners ovate-oblong, apex rounded-denticulate.	Trifolium hybridum
119	Inflorescence rachises sometimes surpassing flowers; banners elliptic, obovate, ovate-oblong, or lanceolate-ovate, apex not denticulate.	> 120
120	Peduncles geniculate or bent proximal to flowers, inflorescences appearing inverted.	> 121
121	Stipule apex long-acuminate, margins entire; corollas 6–10 mm; banners equaling wing and keel petals.	Trifolium breweri
121	Stipules apex acuminate or acute, margins entire proximally, 1–3-toothed distally; corollas 12–15 mm; banners longer than wing and keel petals.	Trifolium latifolium
120	Peduncles straight, inflorescences erect.	> 122
122	Herbs pubescent; stems prostrate; leaflet blades obovate to obcor­date, 0.9–1.6 cm; inflorescences 0.8–1.6 × 0.9–1.6 cm.	Trifolium sonorense
122	Herbs glabrous; stems erect, ascending, or decumbent; leaflet blades ovate, rhombic, elliptic, or lanceolate, 0.5–8 cm; inflorescences 1.5–4 × 1.4–3.5 cm.	> 123
123	Inflorescences longer than wide, rachis internodes between floral whorls elongated; leaflet blades of basal leaves thin, margins setose to dentate.	Trifolium macilentum
123	Inflorescences ± as long as wide, rachis internodes not espe­cially elongated; leaflet blades of basal leaves thick, margins sometimes shortly setose.	Trifolium kingii