Boechera

Á. Löve & D. Löve

Bot. Not. 128: 513. 1976

Etymology: For Tyge Wittrock Böcher, 1909–1983, Danish cytogeneticist who worked on subarctic flowering plants
Treatment appears in FNA Volume 7. Treatment on page 348. Mentioned on page 226, 230, 233, 235, 236, 242, 243, 245, 257, 258, 347, 349, 350, 367.
Perennials or, rarely, biennials; (sexual or apomictic, caudex usually present, rarely absent); not scapose; usually glabrous or pubescent, rarely hirsute or hispid, trichomes simple or branched, 2–14-rayed, sometimes dendritic, not stellate. Stems erect, ascending, or decumbent, unbranched or branched distally. Leaves basal and cauline; petiolate or sessile; basal rosulate or not, petiolate, blade margins usually entire or dentate, rarely lyrate-pinnatifid; cauline usually sessile, rarely shortly petiolate, blade (base sometimes auriculate or sagittate), margins entire or dentate. Racemes (sometimes paniculate), often elongated in fruit. Fruiting pedicels erect, ascending, divaricate, or reflexed (secund or not), slender. Flowers: sepals ovate or oblong, (lateral pair slightly saccate or not basally, margins membranous); petals usually white, pink, lavender, or purple, rarely yellowish, red, or magenta, spatulate or oblanceolate, (claw shorter than sepals or undifferentiated from blade, apex obtuse); stamens tetradynamous; filaments not dilated basally; anthers ovate or oblong, (apex obtuse), [pollen ellipsoid (sexual plants) or spheroid (apomictic)]; nectar glands confluent, subtending bases of stamens, lateral glands semi-annular or annular. Fruits usually sessile, rarely shortly stipitate, usually linear, rarely oblong or lanceolate, straight or falcate, smooth or torulose; valves (papery), each with obscure or prominent midvein, usually glabrous, rarely pubescent; replum (visible), rounded; septum complete, (membranous, veinless); ovules 8–250 per ovary; (style sometimes obsolete); stigma capitate. Seeds usually uniseriate or sub-biseriate, rarely biseriate, flattened, winged, not winged, or margined, oblong or orbicular; seed coat (usually smooth or minutely reticulate, rarely papillate), not mucilaginous when wetted; cotyledons accumbent.

Discussion

Species 111+ (109 in the flora).

Boechera falcata (Turczaninow) Al-Shehbaz is known from eastern Asia (Russian Far East).

Boechera often is treated as a synonym of Arabis (e.g., R. C. Rollins 1993; S. L. Welsh et al. 2003) but it has become clear that morphological similarities between these groups are due to evolutionary convergence, not shared ancestry. Molecular analyses by M. Koch et al. (2001) and T. Mitchell-Olds et al. (2005) revealed that Arabis and Boechera belong to distantly related clades of Brassicaceae that diverged some 19–25 million years ago. A new tribal classification of the family (I. A. Al-Shehbaz et al. 2006) places them in different tribes (Arabideae and Boechereae, respectively), reflecting their substantial molecular divergence.

The taxonomic complexity of Arabis, in the broad sense, is legendary (R. C. Rollins 1941, 1993; G. A. Mulligan 1996). When the genus is split, most of the problematic taxa come to reside in Boechera. A rare confluence of hybridization, apomixis, and polyploidy makes this one of the most difficult genera in the North American flora. The sexual diploid species are relatively distinct from one another, but they hybridize wherever they come into contact. Through apomixis and polyploidy, the hybrids become stable, self-propagating lineages. Most of the hybrid derivatives in Boechera are triploids, but apomictic diploids are known as well. Thus, for any pair of sexual diploid species (e.g., AA and BB), this process can yield different intermediates, including AB apomicts and both possible apomictic triploids (AAB and ABB). The situation becomes even more challenging when a third sexual diploid enters the picture. To date, we have identified three taxa (B. divaricarpa, B. pinetorum, B. tularensis) that appear to be trigenomic triploids. Under these circumstances, even the most distinctive sexual diploid progenitors can become lost in a seemingly continuous range of morphological variability.

In a genus characterized by the presence of polyploids and apomicts, it is essential to know which taxa represent the products of primary, divergent evolution (i.e., sexual diploids) and which are the result of secondary, reticulate evolution. Fortunately, a strong correlation between pollen morphology and ploidy level/reproductive mode facilitates the separation of sexual diploids from polyploids and apomicts in Boechera. Because of differences in meiosis, sexual diploids produce small (13–16 µm diam.), ellipsoid pollen grains with symmetrical colpi. In apomictic individuals, the pollen grains are significantly larger (20–30 µm diam.), and spheroid with asymmetrical colpi. The differences in pollen size and shape are so pronounced that the ploidy level and reproductive mode of most plants with flowers can be determined using a medium power (40×) dissecting microscope (see Fig. 1 in M. D. Windham and I. A. Al-Shehbaz 2006).

To facilitate the study of ploidy level and reproductive mode in Boechera and to allow direct comparison of taxa named by previous authors, we assembled at the Missouri Botanical Garden the holotypes and isotypes of all taxa originally described in Arabis and currently placed in Boechera (over 160 published basionyms). In addition to the types, another 12,000 specimens were examined to document morphological variability and geographic distribution. During this process, we identified additional morphological features (e.g., trichome branching patterns, number of ovules per ovary, pollen and seed morphology) overlooked or underused by previous authors. The result is a substantially revised taxonomy for the genus, the nomenclatural foundation for which was established in a series of papers (M. D. Windham and I. A. Al-Shehbaz 2006, 2007, 2007b).

In many cases, the species circumscriptions adopted here deviate significantly from those of previous authors. Where R. C. Rollins (1993) accepted 63 species with varieties, we recognize 109 species and two with two subspecies. Our treatment includes a total of 71 sexual species. These represent the morphological extremes of the complex and are often easily distinguished (when separated from the apomicts using pollen characters). Although it is likely that some diploid species remain to be discovered, we feel that this portion of the treatment is relatively complete.

Our coverage of the apomictic hybrids is much less comprehensive. There are literally hundreds of hybrids in Boechera with unique genomic combinations, each of which could be recognized at species level. Our treatment includes just 38 apomictic species, primarily taxa recognized at some level by other authors. Because some hybrid combinations are not formally recognized, it is inevitable that some names will be misapplied to superficially similar hybrids of different parentage. For example, plants of B. goodrichii (= B. retrofracta × B. gracilipes), B. consanguinea (= B. retrofracta × B. fendleri), and B. pinetorum (= B. retrofracta × B. rectissima × B. sparsiflora) are sufficiently similar that they might be considered a single taxon if their respective parentages and disjunct geographic ranges were not taken into account. Indeed, all three have been called Arabis holboellii </i>var.<i> pinetorum (e.g., R. C. Rollins 1993; S. L. Welsh et al. 2003), although the epithet consanguinea has priority.

The best way to avoid such misidentification is to pay close attention to the geographic distribution of apomictic taxa and their sexual progenitors. Apomictic hybrids in Boechera appear to be of relatively recent origin and generally have not migrated beyond regions where their parents are sympatric. Thus, users of this treatment should be wary of major range extensions for apomictic taxa; in most cases, these will turn out to be unique hybrid combinations not represented in the keys or descriptions. Because the use of hybrid binomials is potentially misleading, the best approach to identifying a hybrid is to provide a formula name based on the hypothesized parentage (e.g., B. fendleri × B. stricta or B. fendleri hybrid). This requires an accurate understanding of the sexual diploids occurring in the region of interest, which we hope the following keys and descriptions will provide.

Given the inherent taxonomic complexity of Boechera, it has been necessary to incorporate micromorphological characters such as pollen morphology and trichome branching patterns in the identification keys. Whenever possible, we have restricted such characters to later couplets, but microscopic observations are required to distinguish some species. Effective use of the keys also depends on having complete specimens bearing both flowers and fruits. In all cases, measurements of stem length are taken from fruiting plants, those of basal leaves from the largest in the basal rosette, for the fruiting pedicels from the longest in the infructescence, and for the stem trichomes from the largest near the base. Descriptions of the pedicels, flowers, and fruits are taken from the main inflorescence rather its lateral branches, the number of seed rows per locule is determined near the middle of the fruit, and the number of ovules is observed in mature fruits by counting the number of seeds plus the abortive ovules.

Lower Taxa

Boechera acutina, Boechera arcuata, Boechera atrorubens, Boechera bodiensis, Boechera breweri, Boechera burkii, Boechera calderi, Boechera californica, Boechera canadensis, Boechera cascadensis, Boechera cobrensis, Boechera collinsii, Boechera consanguinea, Boechera constancei, Boechera covillei, Boechera crandallii, Boechera cusickii, Boechera davidsonii, Boechera dentata, Boechera depauperata, Boechera dispar, Boechera divaricarpa, Boechera drepanoloba, Boechera duchesnensis, Boechera elkoensis, Boechera evadens, Boechera falcatoria, Boechera falcifructa, Boechera fecunda, Boechera fendleri, Boechera fernaldiana, Boechera formosa, Boechera fructicosa, Boechera glareosa, Boechera glaucovalvula, Boechera goodrichii, Boechera gracilenta, Boechera gracilipes, Boechera grahamii, Boechera gunnisoniana, Boechera harrisonii, Boechera hastatula, Boechera hoffmannii, Boechera holboellii, Boechera horizontalis, Boechera howellii, Boechera inyoensis, Boechera johnstonii, Boechera koehleri, Boechera laevigata, Boechera languida, Boechera lasiocarpa, Boechera lemmonii, Boechera lignifera, Boechera lincolnensis, Boechera lyallii, Boechera macounii, Boechera microphylla, Boechera missouriensis, Boechera nevadensis, Boechera ophira, Boechera oxylobula, Boechera paddoensis, Boechera pallidifolia, Boechera parishii, Boechera pauciflora, Boechera paupercula, Boechera peirsonii, Boechera pendulina, Boechera pendulocarpa, Boechera perennans, Boechera perstellata, Boechera pinetorum, Boechera pinzliae, Boechera platysperma, Boechera polyantha, Boechera porphyrea, Boechera pratincola, Boechera puberula, Boechera pulchra, Boechera pusilla, Boechera pygmaea, Boechera quebecensis, Boechera rectissima, Boechera repanda, Boechera retrofracta, Boechera rigidissima, Boechera rollei, Boechera rollinsiorum, Boechera rubicundula, Boechera saximontana, Boechera schistacea, Boechera serotina, Boechera serpenticola, Boechera shevockii, Boechera shockleyi, Boechera sparsiflora, Boechera spatifolia, Boechera stricta, Boechera subpinnatifida, Boechera suffrutescens, Boechera texana, Boechera tiehmii, Boechera tularensis, Boechera ultra-alsa, Boechera villosa, Boechera williamsii, Boechera xylopoda, Boechera yorkii

Keys

Key to Species Groups of Boechera

1 Cauline leaf blades not auriculate Group 1
1 Cauline leaf blades auriculate > 2
2 Fruit valves pubescent Group 2
2 Fruit valves glabrous > 3
3 Stems glabrous proximally Group 3
3 Stems pubescent proximally > 4
4 Fruits reflexed, pendent, or descending Group 4
4 Fruits erect, ascending, or horizontal Group 5

Group 1

1 Basal leaf blade surfaces glabrous or with simple trichomes only > 2
1 Basal leaf blade surfaces with at least some branched trichomes > 7
2 Biennials, without caudices; stems (2-)3-10 dm; cauline leaves 18-80 > 3
2 Perennials, with caudices; stems 0.3-2.5 dm; cauline leaves 1-12 > 4
3 Racemes usually unbranched; cauline leaves 18-28; ovules 64-80 per ovary; seeds 1.2-1.4 mm wide. Boechera burkii
3 Racemes highly branched; cauline leaves 30-80; ovules 30-42 per ovary; seeds 0.7-1 mm wide. Boechera serotina
4 Fruits pendent; petals white to pale lavender; (c Colorado). Boechera oxylobula
4 Fruits ascending to erect; petals usually purple to lavender (white in B. davidsonii) > 5
5 Leaf blade surfaces puberulent (trichomes simple); petals 4-5 mm; fruits 1-1.5 mm wide. Boechera shevockii
5 Leaf blade surfaces glabrous; petals 6-10 mm; fruits 1.5-2.5 mm wide > 6
6 Caudex branches with persistent, crowded leaf bases; fruits usually ascending, not appressed to rachises; seeds uniseriate. Boechera davidsonii
6 Caudex branches without persistent, crowded leaf bases; fruits erect, appressed to rachises; seeds biseriate or sub-biseriate. Boechera lyallii
7 Styles 2.5-8 mm > 8
7 Styles 0.05-2 mm > 9
8 Petals white, 6-8 mm; basal leaf blade surfaces glabrous; fruits pendent, 4-6(-7.5) cm; n California. Boechera constancei
8 Petals lavender to purple, 8-13 mm; basal leaf blade surfaces pubescent; fruits ascending, 1.5-2.5 cm; s California. Boechera parishii
9 Plants usually glabrous throughout (except margins of basal leaf blades) > 10
9 Plants usually sparsely to densely pubescent proximally (sometimes throughout) > 13
10 Fruits 3-5(-7) mm wide; seeds 3-6 × 2-4 mm > 11
10 Fruits 1.4-2.5 mm wide; seeds 1.5-2.2 × 1-1.5 mm > 12
11 Basal leaf blade margins with 2-4-rayed and simple trichomes; ovules 18-30 per ovary; plants apomictic, pollen spheroid. Boechera covillei
11 Basal leaf blade margins with only 2-rayed and simple trichomes; ovules 10-20 per ovary; plants sexual, pollen ellipsoid. Boechera howellii
12 Petals 6-8.5 mm; fruiting pedicels erect; ovules 34-64 per ovary; seeds biseriate to sub-biseriate, with continuous wing. Boechera lyallii
12 Petals 4-5 mm; fruiting pedicels ascending; ovules 14-22 per ovary; seeds uniseriate, not winged or with distal wing. Boechera tiehmii
13 Fruit valves pubescent > 14
13 Fruit valves glabrous > 20
14 Basal leaf blades 10-25(-50) mm wide; petals 3.5-6 mm. Boechera repanda
14 Basal leaf blades 1-5 mm wide; petals 6-12 mm > 15
15 Fruiting pedicels usually ascending to widely pendent, rarely horizontal. Boechera lincolnensis
15 Fruiting pedicels reflexed, pendent, or recurved > 16
16 Fruiting pedicels 1.5-2 mm; petals yellow proximally, brick-red distally. Boechera yorkii
16 Fruiting pedicels 4-20 mm; petals purple, lavender, or white > 17
17 Stems arising at ground surface, usually without woody bases; seeds uniseriate; ovules 26-64 per ovary > 18
17 Stems elevated above ground surface on woody bases; seeds biseriate; ovules 68-106 per ovary > 19
18 Basal leaf blade margins entire; stems proximally with trichomes 0.05-0.15 mm; cauline leaves 4-10; racemes 5-12-flowered; ovules 26-36 per ovary. Boechera lasiocarpa
18 Basal leaf blade margins usually dentate; stems proximally with trichomes 0.1-0.3(-0.5) mm; cauline leaves 7-45 (-65); racemes 10-40(-64)-flowered; ovules 38-64 per ovary. Boechera puberula
19 Fruiting pedicels not abruptly recurved at base; petals white to lavender; fruits 1.6-3 mm wide, usually not appressed to rachises; seeds 1.2-1.6 × 1-1.2 mm; Colorado Plateau. Boechera formosa
19 Fruiting pedicels abruptly recurved at base; petals usually purple, rarely white; fruits 2.5-4 mm wide, usually appressed to rachises; seeds 1.7-2.8 × 1.5-2.2 mm; California, w Nevada. Boechera pulchra
20 Fruits reflexed, pendent, or descending > 21
20 Fruits erect, ascending, or horizontal > 29
21 Biennials; basal leaf blades 10-30 mm wide. Boechera canadensis
21 Perennials; basal leaf blades 1-7 mm wide > 22
22 Fruits 5-7(-8) mm wide; seeds 4-5 mm wide; primarily Mojave Desert. Boechera glaucovalvula
22 Fruits 0.9-2.3 mm wide; seeds (0.1-)0.6-1.5 mm wide; not Mojave Desert > 23
23 Fruiting pedicels abruptly recurved at bases; fruits reflexed, usually appressed to rachises; cauline leaves 15-40; racemes 15-80 (-140)-flowered. Boechera retrofracta
23 Fruiting pedicels not abruptly recurved at bases; fruits divaricate-descending to pendent, not appressed to rachises; cauline leaves 2-17; racemes 2-13 (-17)-flowered > 24
24 Fruits divaricate-descending to slightly descending, strongly secund > 25
24 Fruits pendent, usually not secund, rarely weakly so > 26
25 Basal leaf blade surfaces with 3-9-rayed trichomes; stems proximally with 2-6-rayed trichomes; seeds 0.9-1.5 mm wide, with continuous wing 0.1-0.5 mm wide; plants sexual, pollen ellipsoid. Boechera lemmonii
25 Basal leaf blade surfaces with 2- or 3-rayed trichomes; stems proximally with simple and 2-rayed trichomes; seeds 0.8-0.9 mm wide, not winged or with distal wing 0.05-0.1 mm wide; plants apomictic, pollen spheroid. Boechera pusilla
26 Basal leaf blade surfaces with 4-8-rayed trichomes > 27
26 Basal leaf blade surfaces with simple and 2- or 3-rayed trichomes > 28
27 Petals 6-10 mm; stems proximally with 4-8-rayed trichomes 0.05-0.15 mm; ovules 26-36 per ovary; seeds uniseriate. Boechera lasiocarpa
27 Petals 4-6 mm; stems proximally with simple and 2-4-rayed trichomes 0.1-0.4 mm; ovules 66-92 per ovary; seeds sub- biseriate. Boechera pendulocarpa
28 Basal leaf blade surfaces with 2- or 3-rayed trichomes 0.1-0.4 mm; ovules 28-44 per ovary; seeds uniseriate, with continuous wing; c Colorado. Boechera oxylobula
28 Basal leaf blade surfaces with simple and 2-rayed trichomes 0.3-0.8 mm; ovules 40-70(-100) per ovary; seeds biseriate, usually not winged; not c Colorado. Boechera pendulina
29 Fruits secund > 30
29 Fruits not secund > 31
30 Basal leaf blade surfaces with 3-9-rayed trichomes; stems proximally with 2-6- rayed trichomes; seeds 1-1.5 mm wide, with continuous wing 0.1-0.5 mm wide; plants sexual, pollen ellipsoid. Boechera lemmonii
30 Basal leaf blade surfaces with 2- or 3-rayed trichomes or glabrous; stems proximally with simple and 2-rayed trichomes; seeds 0.8-0.9 mm wide, not winged or with distal wing 0.05-0.1 mm wide; plants apomictic, pollen spheroid. Boechera pusilla
31 Stems proximally with simple trichomes 0.5-1.5 mm; ovules 56-106 per ovary. Boechera cusickii
31 Stems proximally with simple and/or branched trichomes usually less than 0.5 mm; ovules 8-52 per ovary > 32
32 Fruits 1.3-1.7(-2) mm wide, erect, appressed to rachises. Boechera paupercula
32 Fruits 2-5.5 mm wide, divaricate-ascending to erect, ± appressed to rachises > 33
33 Basal leaf blades 7-25(-50) mm wide, margins usually repand to dentate, rarely entire. Boechera repanda
33 Basal leaf blades 0.8-7(-10) mm wide, margins entire > 34
34 Basal leaf blade surfaces with at least some 8-14-rayed trichomes > 35
34 Basal leaf blade surfaces with 2-6 (or 7)-rayed trichomes only > 36
35 Petals 3.5-6 mm; styles to 0.1 mm; ovules 44-52 per ovary; cauline leaves 1-5. Boechera dispar
35 Petals 9-14 mm; styles (0.7-)1-2 mm; ovules 26-34 per ovary; cauline leaves 4-10. Boechera johnstonii
36 Stems proximally with simple and branched trichomes; fruits (1.3-)2-3.3 cm; ovules 8-12 per ovary. Boechera pygmaea
36 Stems proximally with branched trichomes only; fruits (2.5-) 3-8.5 cm; ovules 16-44 per ovary > 37
37 Fruits 3-5.5 mm wide; seeds 3-6.5(-8) × 2-4.5 mm, wing (0.8-)1.2-2.5 mm wide > 38
37 Fruits 2-3.2 mm wide; seeds 2.5-3.5 × 1.5-2.5 mm, wing 0.2-0.9 mm wide > 39
38 Basal leaf petioles with simple or spurred cilia to 1 mm, blade surfaces with short-stalked, 2-4 (or 5)-rayed trichomes 0.1-0.3 mm; fruits without parallel edges (undulate and constricted between seeds). Boechera platysperma
38 Basal leaf petioles without cilia, blade surfaces with long-stalked, 3-6 (or 7)-rayed trichomes 0.2-0.5 mm; fruits with parallel edges (not undulate and constricted between seeds). Boechera ultra-alsa
39 Sepals glabrous; basal leaf blades 2-6 mm wide, with sessile or subsessile trichomes; fruiting pedicels 4-8 mm; fruits erect-ascending, often appressed to rachises. Boechera elkoensis
39 Sepals sparsely pubescent; basal leaf blades 1-2.5(-3) mm wide, with stalked trichomes; fruiting pedicels 2-6 mm; fruits ascending, not appressed to rachises. Boechera pinzliae

Group 2

1 Petals 2-4 mm; fruits 0.7-1 mm wide; seeds not winged; basal leaf blades (5-)10-45 mm wide > 2
1 Petals 4-16 mm; fruits 0.9-3(-4) mm wide; seeds usually winged; basal leaf blades 1-7(-11) mm wide > 3
2 Basal leaf blade adaxial surfaces with simple trichomes; petals white to cream; fruiting pedicels 1-3(-6) mm. Boechera dentata
2 Basal leaf blade adaxial surfaces with 3- or 4(-6)-rayed trichomes; petals purplish; fruiting pedicels (5-)7-15 mm. Boechera perstellata
3 Fruiting pedicels reflexed, pendent, or descending > 4
3 Fruiting pedicels suberect, ascending, or horizontal > 10
4 Petals white to lavender; fruits 0.9-2.2 mm wide; seeds 0.9-1.8 × 0.7-1.4 mm > 5
4 Petals usually purple; fruits (1.6-)2-4 mm wide; seeds 1.7-3.5 × 1.3-2.2 mm > 7
5 Fruiting pedicels not abruptly recurved at bases; fruits 1.9-2.2 mm wide, pendent, rarely appressed to rachises; ovules 38-64 per ovary; seeds 1.4-1.8 mm, wing 0.1-0.3 mm wide. Boechera puberula
5 Fruiting pedicels abruptly recurved at bases; fruits 0.9-1.5 mm wide, reflexed, usually appressed to rachises; ovules 60-116 per ovary; seeds 0.9-1.4 mm, wing 0.05-0.1 mm wide > 6
6 Fruit valves densely pubescent; petals sparsely pubescent abaxially. Boechera polyantha
6 Fruit valves sparsely pubescent; petals glabrous abaxially. Boechera retrofracta
7 Stems from near ground surface, usually without woody bases; seeds uniseriate; ovules 20-42 per ovary; north of 40oN latitude > 8
7 Stems elevated above ground surface on woody bases; seeds biseriate to sub-biseriate; ovules 68-126 per ovary; south of 40oN latitude > 9
8 Basal leaf blade margins entire; petals 6-8 mm; styles 1.5-2 mm; fruits divaricate-descending, valves sparsely pubescent. Boechera serpenticola
8 Basal leaf blade margins (at least some) prominently dentate or subpinnatifid; petals 9-14 mm; styles 0.5-1 mm; fruits pendent, valves moderately to densely pubescent. Boechera subpinnatifida
9 Fruiting pedicels abruptly recurved at bases; fruits 2.5-4 mm wide, valves densely pubescent proximally; basal leaf blades 1-3 mm wide. Boechera pulchra
9 Fruiting pedicels not abruptly recurved at bases; fruits 2-2.5 mm wide, valves glabrous proximally; basal leaf blades 3-7 mm wide. Boechera xylopoda
10 Stems proximally with simple and 2-rayed trichomes 0.4-1 mm; basal leaf blade surfaces with long-stalked, 2-4-rayed trichomes. Boechera breweri
10 Stems proximally with 2-12-rayed trichomes 0.1-0.5 mm; basal leaf blade surfaces with short-stalked, (3- or) 4-12-rayed trichomes > 11
11 Fruits (4.5-)6-11 cm, usually curved; petals 0.8-1.2 mm wide; ovules 140-190 per ovary. Boechera shockleyi
11 Fruits 3-5.8 cm, straight; petals 1.5-4.5 mm wide; ovules 34-120 per ovary > 12
12 Styles 1-1.5 mm; seeds uniseriate; ovules 34-68 per ovary; stems proximally with 5-10-rayed trichomes; w Montana. Boechera fecunda
12 Styles 0.1-0.3 mm; seeds biseriate or sub-biseriate; ovules 72-120 per ovary; stems proximally with 2-7-rayed trichomes; sw United States > 13
13 Fruit valves glabrous proximally; cauline leaves 3-8; basal leaves 2-5 mm wide; fruiting pedicels 7-14 mm. Boechera duchesnensis
13 Fruit valves pubescent proximally; cauline leaves 10-25; basal leaves 1-2 mm wide; fruiting pedicels 10-20(-25) mm. Boechera lincolnensis

Group 3

1 Fruits erect, usually appressed to rachises > 2
1 Fruits reflexed, pendent, horizontal, or ascending, not appressed to rachises or, if so, reflexed > 5
2 Basal leaf blade surfaces with 4-8-rayed trichomes; petals 3-4 mm; seeds 0.7-0.9 × 0.5-0.6 mm. Boechera williamsii
2 Basal leaf blade surfaces glabrous or with 2-4(-6)-rayed trichomes; petals 5-11 mm; seeds 1.3-2.2 × 1-1.8 mm > 3
3 Basal leaf blade surfaces with malpighiaceous (usually along margins) and sessile, 3- or 4-rayed trichomes. Boechera calderi
3 Basal leaf blade surfaces either with malpighiaceous or with short-stalked 2-4(-6)-rayed trichomes (rarely completely glabrous) > 4
4 Basal leaves usually with short-stalked, 2-4(-6)-rayed trichomes (at least on margins), malpighiaceous trichomes absent; petals lavender to purple; cauline leaves 1-5; ovules 34-64 per ovary. Boechera lyallii
4 Basal leaves with exclusively malpighiaceous trichomes (rarely with simple cilia on petioles); petals usually white, rarely lavender; cauline leaves 6-52; ovules 110-216 per ovary. Boechera stricta
5 Fruits pendent to reflexed > 6
5 Fruits ascending, horizontal, or slightly descending > 13
6 Fruiting pedicels (at least some) abruptly recurved at bases > 7
6 Fruiting pedicels not abruptly recurved at bases > 9
7 Stems elevated above ground surface on woody bases; fruits 3-5(-6) mm wide; seeds with wings 0.8-1.5 mm wide; racemes 6-12-flowered. Boechera suffrutescens
7 Stems from ground surface, usually without woody bases; fruits 1-2.5 mm wide; seeds with wings 0.05-0.25 mm wide; racemes 10-50-flowered > 8
8 Petals lavender, 5-6 mm; basal leaf blade surfaces glabrous or with 3-6-rayed trichomes; fruits 1-1.5 mm wide; ne Oregon. Boechera hastatula
8 Petals white, 3-4 mm; basal leaf blade surfaces with simple and 2- or 3-rayed trichomes; fruits 1.8-2.5 mm wide; California to sc Oregon. Boechera rectissima
9 Fruits 1.5-2.5 mm wide; stems arising from margins of rosettes or arising laterally to sterile shoots > 10
9 Fruits 2.5-5(-6) mm wide; stems arising from centers of rosettes > 11
10 Fruiting pedicels 10-27 mm; basal leaf blade surfaces with 2-6-rayed trichomes; cauline leaf blades with auricles 0.5-3.5(-5.5) mm; s New Mexico. Boechera porphyrea
10 Fruiting pedicels 5-9 mm; basal leaf blade surfaces glabrous or with 2- or 3-rayed trichomes; cauline leaf blades with auricles 0.2-0.5 mm; c Nevada to w Utah. Boechera schistacea
11 Basal leaf blade surfaces with trichomes 0.4-0.6 mm; ovules 80-130 per ovary; seeds biseriate, wing 0.1-0.15 mm wide; New Mexico, Texas. Boechera texana
11 Basal leaf blade surfaces glabrous or with trichomes 0.07-0.4 mm; ovules 14-30 per ovary; seeds uniseriate, wing 0.3-1.5 mm wide; California, Idaho, Nevada, Oregon, Washington > 12
12 Petals 8-11 mm; fruits 2.5-3.5 mm wide; seeds with wing 0.3-0.6 mm wide; racemes 3-7-flowered. Boechera rollei
12 Petals 4.5-6 mm; fruits 3-5(-6) mm wide; seeds with wing 0.8-1.5 mm wide; racemes 6-12-flowered. Boechera suffrutescens
13 Basal leaf blade surfaces glabrous or with simple trichomes only > 14
13 Basal leaf blade surfaces with branched trichomes only > 16
14 Basal leaf blade margins entire; fruits 1.9-4 cm; seeds biseriate; Nevada. Boechera nevadensis
14 Basal leaf blade margins dentate to lyrate-pinnatifid; fruits (4-)6-11.7 cm; seeds uniseriate; not Nevada > 15
15 Basal leaf blade margins dentate or serrate; petals 3-5 mm. Boechera laevigata
15 Basal leaf blade margins lyrate-pinnatifid; petals 5-10 mm. Boechera missouriensis
16 Basal leaf blade trichomes sessile or subsessile > 17
16 Basal leaf blade trichomes stalked > 19
17 Fruits secund, 2-3.5 mm wide; ovules 44-76(-104) per ovary; racemes 8-15-flowered. Boechera drepanoloba
17 Fruits not secund, 1-2.5 mm wide; ovules 84-146 per ovary; racemes 12-88-flowered > 18
18 Petals usually purple, rarely lavender, 1.5-3 mm wide; fruits 1.7-2.5 mm wide; seeds 1-1.5 mm wide. Boechera divaricarpa
18 Petals usually white, rarely lavender, 1-2 mm wide; fruits 1-1.8 mm wide; seeds 0.8-1.2 mm wide. Boechera grahamii
19 Fruits 6-10 cm; seeds biseriate; ovules 170-220 per ovary; cauline leaves 15-65; Channel Islands, California. Boechera hoffmannii
19 Fruits 1.5-5.5(-6.5) cm; seeds uniseriate; ovules 10-86 per ovary; cauline leaves 2-12; not Channel Islands, California > 20
20 Fruits 3-5(-7) mm wide; seeds 3-6 × 2-4 mm > 21
20 Fruits 1-3 mm wide; seeds 1-2.2 × 0.8-1.6 mm > 22
21 Basal leaf blade margins with some 4-rayed trichomes; ovules 18-30 per ovary; plants apomictic, pollen spheroid. Boechera covillei
21 Basal leaf blade margins without 4-rayed trichomes; ovules 10-20 per ovary; plants sexual, pollen ellipsoid. Boechera howellii
22 Fruits secund > 23
22 Fruits not secund > 25
23 Basal leaf blade surfaces glabrous or with 2- or 3-rayed trichomes; seeds 0.8-0.9 mm wide, not winged or with distal wing 0.05-0.1 mm wide. Boechera pusilla
23 Basal leaf blade surfaces with 3-9-rayed trichomes; seeds 0.9-1.5 mm wide, with continuous wing 0.1-0.5 mm wide > 24
24 Cauline leaf blades with auricles to 0.5 mm; ovules 28-44 per ovary; basal leaves densely or sparsely pubescent, petioles ciliate. Boechera lemmonii
24 Cauline leaf blades with auricles 1-2 mm; ovules 42-54 per ovary; basal leaves sparsely pubescent, petioles not ciliate. Boechera paddoensis
25 Basal leaf blade surfaces glabrous, margins with simple or 2- or 3-rayed trichomes; ovules 14-22 per ovary; plants sexual, pollen ellipsoid. Boechera tiehmii
25 Basal leaf blade surfaces and margins with 2-10-rayed trichomes; ovules 48-86 per ovary; plants apomictic, pollen spheroid > 26
26 Fruiting pedicels 8-12 mm; basal leaf blade surfaces with 2-5-rayed trichomes; stems from margins of rosettes; n Utah. Boechera harrisonii
26 Fruiting pedicels 2-6 mm; basal leaf blade surfaces with 4-7-rayed trichomes; stems from centers of rosettes; s California. Boechera peirsonii

Group 4

1 Fruiting pedicels usually abruptly recurved at bases > 2
1 Fruiting pedicels usually not abruptly recurved at bases (except B. subpinnatifida) > 7
2 Fruits 3-6 mm wide; ovules 20-30 per ovary; racemes 6-12-flowered. Boechera suffrutescens
2 Fruits 0.9-2.5 mm wide; ovules 46-126 per ovary; racemes 10-140-flowered > 3
3 Stems proximally with branched trichomes only > 4
3 Stems proximally with simple and branched trichomes, or simple trichomes only > 5
4 Fruits (2-)2.2-2.5 mm wide, descending, not appressed to rachises, strongly secund; Greenland. Boechera holboellii
4 Fruits 0.9-1.5 mm wide, reflexed, usually appressed to rachises, usually not secund, rarely so; not Greenland. Boechera retrofracta
5 Stems proximally with simple trichomes only; petals 3-4 mm; ovules 46-80 per ovary. Boechera rectissima
5 Stems proximally with simple and branched trichomes; petals 4-6 mm; ovules 70-126 per ovary > 6
6 Basal leaf blade surfaces with 5-8-rayed trichomes; fruits 0.9-1.5 mm wide; seeds 1-1.4 × 0.8-1 mm; plants sexual, pollen ellipsoid. Boechera collinsii
6 Basal leaf blade surfaces with 2-4 (or 5)-rayed trichomes; fruits 1.5-2 mm wide; seeds 1.5-1.8 × 1.2-1.5 mm; plants apomictic, pollen spheroid. Boechera pinetorum
7 Fruiting pedicels sparsely to densely pubescent > 8
7 Fruiting pedicels usually glabrous, rarely with few isolated trichomes present > 23
8 Stems proximally with simple and branched trichomes, or simple trichomes only > 9
8 Stems proximally with branched trichomes only > 14
9 Stems proximally with simple trichomes only; fruits 2.5-4 mm wide; seeds with wing 0.4-1 mm wide. Boechera canadensis
9 Stems proximally with simple and branched trichomes; fruits 0.8-2.5 mm wide; seeds with wing 0.05-0.3 mm wide > 10
10 Petals purple to magenta, 8-12 × 2.5-4 mm; stems elevated above ground surface on woody base; caudices with persistent (peg-like) leaf bases. Boechera koehleri
10 Petals lavender to white, 4-8 × 0.5-2 mm; stems from near ground surface, without woody base; caudices without persistent leaf bases > 11
11 Fruits 2.5-4 cm; ovules 36-54 per ovary; stems usually 2-6 per caudex branch, arising from margins of rosettes; racemes 7-15-flowered; plants sexual, pollen ellipsoid. Boechera gunnisoniana
11 Fruits 4-10.5 cm; ovules 56-162 per ovary; stems usually 1 per caudex branch, arising from centers of rosettes; racemes 10-63-flowered; plants apomictic, pollen spheroid > 12
12 Fruits reflexed; fruiting pedicels with few simple and 2-rayed trichomes. Boechera pinetorum
12 Fruits pendent, horizontal, divaricate, ascending, or descending; fruiting pedicels with many 2- or 3-rayed trichomes > 13
13 Petals 4-5 mm; fruits 0.8-1.2 mm wide; ovules 56-78 per ovary; cauline leaf blades with auricles 0.5-1.5 mm; basal leaf blade surfaces with 3-6-rayed trichomes 0.07-0.3 mm. Boechera macounii
13 Petals 5-8 mm; fruits 1.5-2.2 mm wide; ovules 80-162 per ovary; cauline leaf blades with auricles (1-)3-10 mm; basal leaf blade surfaces with 2-5-rayed trichomes 0.3-0.6 mm. Boechera pauciflora
14 Stems arising from margins of rosettes, elevated above ground surface on woody bases. Boechera rollinsiorum
14 Stems arising from centers of rosettes, produced near ground surface, usually without woody bases (except B. californica) > 15
15 Ovules 14-44 per ovary (-64 in B. cobrensis); plants sexual, pollen ellipsoid > 16
15 Ovules (56-)68-180 per ovary; plants apomictic, pollen spheroid > 19
16 Fruits 0.7-0.8 mm wide; seeds 0.7-1.1 × 0.5-0.6 mm, not winged; basal leaf blade surfaces with simple trichomes adaxially. Boechera dentata
16 Fruits 1.6-3 mm wide; seeds 1.3-3.5 × 1-2.2 mm, winged; basal leaf blade surfaces with (2-)4-10-rayed trichomes adaxially > 17
17 Petals 9-14 mm; basal leaf blade margins (at least some) prominently dentate or subpinnatifid; cauline leaves (10-)20-60. Boechera subpinnatifida
17 Petals 3.5-8 mm; basal leaf blade margins entire; cauline leaves 2-12(-14) > 18
18 Petals lavender to white, 3.5-6 mm; styles to 0.2 mm; ovules 34-64 per ovary; sandy habitats in California, Idaho, Nevada, Oregon, Wyoming. Boechera cobrensis
18 Petals purple, 6-8 mm; styles 1.5-2 mm; ovules 20-24 per ovary; serpentine outcrops in nw California. Boechera serpenticola
19 Petals 9-14 mm; fruits (6-)8-12 cm; ovules 140-180 per ovary; s California. Boechera californica
19 Petals 5-8.5 mm; fruits 3-6.5 cm; ovules 56-134 per ovary; California, Colorado, Nevada, New Mexico, Utah > 20
20 Cauline leaves 5-9, not concealing stem proximally; styles 0.5-1 mm; ovules 62-80 per ovary; seeds uniseriate. Boechera falcifructa
20 Cauline leaves (7-)12-72, often concealing stem proximally; styles 0.05-0.5 mm; ovules 74-136 per ovary; seeds usually biseriate or sub-biseriate (rarely uniseriate in B. inyoensis) > 21
21 Stems proximally with 7-12-rayed trichomes. Boechera inyoensis
21 Stems proximally with 2-8-rayed trichomes > 22
22 Fruiting pedicels 8-14 mm; stems proximally with 2-6-rayed trichomes; fruits 1-2 mm wide; Four Corners region. Boechera consanguinea
22 Fruiting pedicels (10-)15-28 mm; stems proximally with 4-8-rayed trichomes; fruits 1.5-2.9 mm wide; e Nevada, w Utah. Boechera goodrichii
23 Seeds biseriate or sub-biseriate > 24
23 Seeds usually uniseriate > 33
24 Stems proximally with subsessile, submalpighiaceous trichomes; seeds 2-2.5 × 1.1-1.5 mm; (s Sierra Nevada). Boechera tularensis
24 Stems proximally with simple and/or stalked, branched trichomes; seeds 0.7-1.8 × 0.5-1.2 mm > 25
25 Stems proximally with 2-8-rayed trichomes; plants apomictic, pollen spheroid > 26
25 Stems proximally with simple, spurred, or 2- or 3-rayed trichomes; plants sexual, pollen ellipsoid (except B. languida) > 29
26 Fruiting pedicels divaricate-ascending to horizontal; stems proximally with simple and 2-4-rayed trichomes > 27
26 Fruiting pedicels reflexed or divaricate-descending; stems proximally with 2-8-rayed trichomes > 28
27 Sepals pubescent; fruiting pedicels divaricate-ascending; fruits 1.7-2 mm wide; ovules 60-96 per ovary; Colorado Plateau and vicinity. Boechera gracilenta
27 Sepals glabrous; fruiting pedicels horizontal; fruits 1.8-2.5 mm wide; ovules 100-160 per ovary; s New Mexico, w Texas. Boechera porphyrea
28 Fruiting pedicels 8-14 mm; stems proximally with 2-6-rayed trichomes; fruits1-2 mm wide; Four Corners region. Boechera consanguinea
28 Fruiting pedicels (10-)15-28 mm; stems proximally with 4-8-rayed trichomes; fruits (1.5-)2-3 mm wide; e Nevada, w Utah. Boechera goodrichii
29 Cauline leaves 30-65; fruiting pedicels (15-)20-47 mm; ovules 130-210 per ovary. Boechera gracilipes
29 Cauline leaves 3-25; fruiting pedicels 3-15(-23) mm; ovules 40-128 per ovary > 30
30 Cauline leaves usually concealing stem proximally; ovules 90-128 per ovary > 31
30 Cauline leaves not concealing stem proximally; ovules 40-70(-90) per ovary > 32
31 Petals 5-9 × 1-2 mm; fruiting pedicels 9-18(-23) mm; Colorado Plateau, s Nevada. Boechera fendleri
31 Petals 3-3.7(-4) × 0.5-0.8 mm; fruiting pedicels 6-10(-15) mm; mountains of c Colorado, nc North Mexico. Boechera spatifolia
32 Basal leaf blade surfaces densely pubescent, trichomes simple and 2-4-rayed; seeds sub-biseriate; cauline leaf blades with auricles 0.5-1.5 mm; racemes 10-20-flowered; plants apomictic, pollen spheroid; s Wyoming. Boechera languida
32 Basal leaf blade surfaces sparsely pubescent, trichomes simple and 2-rayed; seeds biseriate; cauline leaf blades with auricles to 0.7 mm; racemes 4-14-flowered; plants sexual, pollen ellipsoid; Arizona, California, Colorado, Nevada, Utah, Wyoming. Boechera pendulina
33 Stems proximally with simple trichomes only. Boechera canadensis
33 Stems proximally usually with simple and/or branched trichomes (rarely all simple in B. pusilla) > 34
34 Fruits 3-5(-6) mm wide; seeds winged, wings 0.8-1.5 mm wide; stems elevated above ground surface on woody bases. Boechera suffrutescens
34 Fruits 0.7-3.5 mm wide; seeds not winged, or wings 0.05-1 mm wide; stems usually not from above ground surface on woody bases (except B. perennans and B. lignifera) > 35
35 Fruits reflexed to closely pendent. Boechera pinetorum
35 Fruits descending to ascending or widely pendent > 36
36 Fruits 0.7-0.8 mm wide; petals 2-3.5 mm; basal leaf blade surfaces with simple trichomes adaxially. Boechera dentata
36 Fruits 1-3.5 mm wide; petals 3.5-8(-9) mm; basal leaf blade surfaces with branched trichomes adaxially > 37
37 Stems proximally with simple and branched trichomes > 38
37 Stems proximally with branched trichomes only > 41
38 Stems proximally with sessile or subsessile, 2- or 3(-6)-rayed trichomes. Boechera grahamii
38 Stems proximally with stalked, 2-5-rayed trichomes > 39
39 Basal leaf blade margins dentate, 3-15(-20) mm wide; fruiting pedicels (6-)10-25 mm; ovules 60-96 per ovary; stems (1.5-)2-7 dm. Boechera perennans
39 Basal leaf blade margins entire, 1-3(-4) mm wide; fruiting pedicels 2-7 mm; ovules 20-54 per ovary; stems 0.5-2(-2.5) dm > 40
40 Basal leaf blade surfaces densely pubescent, trichomes 3-6-rayed; fruits not secund, 1-1.5 mm wide; ovules 36-54 per ovary; seeds with continuous wing 0.1-0.15 mm wide; plants sexual, pollen ellipsoid; c Colorado. Boechera gunnisoniana
40 Basal leaf blade surfaces sparsely pubescent, trichomes 2- or 3-rayed; fruits secund, 1.5-2 mm wide; ovules 20-32 per ovary; seeds not winged or with distal wing 0.05-0.1 mm wide; plants apomictic, pollen spheroid; c Wyoming. Boechera pusilla
41 Fruits secund > 42
41 Fruits not secund > 45
42 Petals white; Quebec. Boechera quebecensis
42 Petals purple to lavender; not Quebec > 43
43 Stems proximally with sessile and subsessile, 2- or 3-rayed trichomes; petals 6-8 mm; plants usually short-lived perennials, without woody caudices. Boechera drepanoloba
43 Stems proximally with stalked, 2-6-rayed trichomes; petals 3.5-6 mm; plants long-lived perennials, with woody caudices > 44
44 Cauline leaf blades with auricles 0.5-1.5 mm; petals 1.5-2 mm wide; fruiting pedicels 4-11 mm; fruits 2-3 mm wide; ovules 40-54 per ovary; seeds 2-2.5 × 1.7-2 mm; sc Oregon. Boechera horizontalis
44 Cauline leaf blades with auricles to 0.5 mm; petals 1-1.5 mm wide; fruiting pedicels 2-6 mm; fruits 1.6-2.3 mm wide; ovules 28-44 per ovary; seeds 1.3-2 × 1-1.5 mm; Alaska, Alberta, British Columbia, California, Colorado, Idaho, Montana, Nevada, Oregon, Utah, Washington, Wyoming, Yukon. Boechera lemmonii
45 Basal leaf blade margins dentate; stems proximally with 2-5-rayed trichomes > 46
45 Basal leaf blade margins entire; stems proximally with (3 or) 4-10-rayed trichomes > 47
46 Basal leaf blade surfaces with trichomes 0.05-0.2 mm; fruiting pedicels 5-10 mm; fruits 1.5-1.8 mm wide; seeds with distal wing; plants apomictic, pollen spheroid; nw Wyoming. Boechera fructicosa
46 Basal leaf blade surfaces with trichomes 0.2-0.4 mm; fruiting pedicels (6-)10-25 mm; fruits 1.7-2.1 mm wide; seeds with continuous wing; plants sexual, pollen ellipsoid; Arizona, California, Nevada, New Mexico, Texas, Utah. Boechera perennans
47 Stems usually 1 per caudex branch, arising from centers of rosettes; petals 0.7-1 mm wide; seeds with wings 0.25-0.5 mm wide; fruits 1.7-2.5 mm wide. Boechera cobrensis
47 Stems usually 2-5 per caudex branch, arising laterally proximal to sterile shoots; petals 1-1.5 mm wide; seeds with wings 0.1-0.15 mm wide; fruits 1.2-2 mm wide. Boechera lignifera

Group 5

1 Basal leaf blade surfaces with branched trichomes sessile, 2-rayed (malpighiaceous). Boechera stricta
1 Basal leaf blade surfaces with branched trichomes stalked or, if sessile, some more than 2-rayed > 2
2 Stems proximally with branched trichomes only > 3
2 Stems proximally with simple and/or branched trichomes or glabrous > 27
3 Fruits secund > 4
3 Fruits not secund > 7
4 Petals white; Quebec. Boechera quebecensis
4 Petals purple to lavender; not Quebec > 5
5 Stems proximally with sessile and subsessile, 2- or 3-rayed trichomes; petals 6-8 mm; seeds sub-biseriate; plants usually short-lived perennials, without woody caudices. Boechera drepanoloba
5 Stems proximally with stalked, 2-6-rayed trichomes; petals 3.5-6 mm; seeds uniseriate; plants long-lived perennials, with woody caudices > 6
6 Cauline leaf blades with auricles 0.5-1.5 mm; petals 1.5-2 mm wide; fruiting pedicels 4-11 mm; fruits 2-3 mm wide; ovules 40-54 per ovary; seeds 2-2.5 × 1.7-2 mm; sc Oregon. Boechera horizontalis
6 Cauline leaf blades with auricles to 0.5 mm; petals 1-1.5 mm wide; fruiting pedicels 2-6 mm; fruits 1.6-2.3 mm wide; ovules 28-44 per ovary; seeds 1.3-2 × 1-1.5 mm; Alaska, Alberta, British Columbia, California, Colorado, Idaho, Montana, Nevada, Oregon, Utah, Washington, Wyoming, Yukon. Boechera lemmonii
7 Biennials, without caudices; petals 2-3.5 mm; fruits 0.7-0.8 mm wide. Boechera dentata
7 Perennials or, rarely, biennials, often with caudices (well-developed); petals 3.5-14 mm; fruits 0.9-3.2 mm wide > 8
8 Stems proximally with 4-12-rayed trichomes only > 9
8 Stems proximally with at least some 2- or 3-rayed trichomes, sometimes mixed with 4-6-rayed ones > 14
9 Cauline leaves concealing stems proximally; stems proximally with 7-12-rayed trichomes; ovules 74-190 per ovary > 10
9 Cauline leaves not concealing stems proximally; stems proximally with 4-8 (-10)-rayed trichomes; ovules 30-84 per ovary > 11
10 Petals 1.2-2 mm wide; basal leaves ciliate proximally, surfaces with trichomes 0.2-0.7 mm; ovules 74-134 per ovary; seeds 1.7-2 × 1-1.5 mm, with continuous wing; plants apomictic, pollen spheroid. Boechera inyoensis
10 Petals 0.8-1.2 mm wide; basal leaves not ciliate proximally, surfaces with trichomes 0.1-0.2 mm; ovules 140-190 per ovary; seeds 1-1.3 × 0.7-0.8 mm, usually with distal wing, rarely not winged; plants sexual, pollen ellipsoid. Boechera shockleyi
11 Petals 3.5-5 mm; fruiting pedicels 1.5-5(-7) mm; plants apomictic, pollen spheroid; e California, w Nevada > 12
11 Petals 5-12 mm; fruiting pedicels 5-20 mm; plants sexual, pollen ellipsoid; Colorado, c Nevada, Utah > 13
12 Stems 1.5-3.5 dm; fruits 4-6.2 cm; ovules 48-68 per ovary. Boechera bodiensis
12 Stems 0.5-1.5(-2) dm; fruits 1.7-3.5(-4.5) cm; ovules 32-44 per ovary. Boechera depauperata
13 Petals 5-7 mm; basal leaf blade surfaces with trichomes 0.1-0.2 mm; seeds 0.8-1 mm; c Colorado. Boechera crandallii
13 Petals 7-12 mm; basal leaf blade surfaces with trichomes 0.04-0.1 mm; seeds 1-1.2 mm; nw Colorado, Nevada, Utah. Boechera fernaldiana
14 Fruits erect to suberect, usually appressed to rachises > 15
14 Fruits horizontal to ascending, or pendent, not appressed to rachises > 17
15 Racemes (7-)14-45-flowered; petals 6-10 mm; ovules 60-140 per ovary. Boechera pratincola
15 Racemes 4-15-flowered; petals 4-7 mm; ovules 24-60 per ovary > 16
16 Basal leaf blade surfaces with sessile or subsessile trichomes; fruits 2-3 mm wide; stems 1-3 dm; plants apomictic, pollen spheroid. Boechera elkoensis
16 Basal leaf blade surfaces with stalked trichomes; fruits 1.2-1.8 mm wide; stems 0.4-1.4 dm; plants sexual, pollen ellipsoid. Boechera ophira
17 Racemes 30-120-flowered; fruits 6-12 cm; ovules 140-220 per ovary; s California > 18
17 Racemes 4-25(-36)-flowered; fruits 2-6.5(-7.5) cm; ovules 26-112 per ovary; not s California (except B. peirsonii) > 19
18 Petals purple, 9-14 mm; fruits 1.5-2.5 mm wide; ovules 140-180 per ovary; fruiting pedicels 4-15(-20) mm; plants apomictic, pollen spheroid. Boechera californica
18 Petals white or lavender, 8-10 mm; fruits 2.5-3 mm wide; ovules 170-220 per ovary; fruiting pedicels 10-45 mm; plants sexual, pollen ellipsoid. Boechera hoffmannii
19 Stems usually 2-5 per caudex branch, arising from margins of rosettes or laterally proximal to sterile shoots > 20
19 Stems usually 1 per caudex branch, arising from centers of rosettes > 23
20 Fruits 2-3.2 mm wide; ovules 26-42 per ovary; seeds 2.5-3.5 × 1.5-2.5 mm; e California, Nevada > 21
20 Fruits 1-2 mm wide; ovules 44-86 per ovary; seeds 1.1-1.3 × 0.8-1.1 mm; Colorado Plateau, nc Utah > 22
21 Sepals glabrous; basal leaf blades 2-6 mm wide, surfaces with sessile or subsessile trichomes; fruiting pedicels 4-8 mm. Boechera elkoensis
21 Sepals sparsely pubescent; basal leaf blades 1-2.5(-3) mm wide, surfaces with stalked trichomes; fruiting pedicels 2-6 mm. Boechera pinzliae
22 Basal leaf blades 2-4 mm wide, surfaces with 2-5-rayed trichomes; ovules 64-86 per ovary; plants apomictic, pollen spheroid; nc Utah. Boechera harrisonii
22 Basal leaf blades 5-11(-13) mm wide, surfaces with 4-8- rayed trichomes; ovules 44-62 per ovary; plants sexual, pollen ellipsoid; Colorado Plateau. Boechera pallidifolia
23 Petals 7-12 mm. Boechera fernaldiana
23 Petals 4-7 mm > 24
24 Basal leaf blade surfaces with 2- or 3-rayed trichomes only; plants sexual, pollen ellipsoid; Nevada. Boechera ophira
24 Basal leaf blade surfaces with 3-8-rayed trichomes; plants apomictic, pollen spheroid; not Nevada > 25
25 Plants cespitose, long-lived; fruits 2-2.8 mm wide; petals purple; s California. Boechera peirsonii
25 Plants not cespitose, short-lived; fruits 1.2-1.8 mm wide; petals white or lavender; n California, Idaho, Oregon, Wyoming > 26
26 Basal leaf blade surfaces with sessile trichomes 0.15-0.35 mm; petals 5-7 mm; seeds 1.8-2.2 × 1-1.4 mm; n California, Oregon. Boechera acutina
26 Basal leaf blade surfaces with short-stalked trichomes 0.04-0.15 mm; petals 4-5 mm; seeds 1.1-1.4 × 0.7-0.9 mm; Idaho, Wyoming. Boechera saximontana
27 Stems proximally with simple trichomes only > 28
27 Stems proximally with simple and/or branched trichomes or glabrous (in B. rigidissima) > 31
28 Basal leaf blade margins lyrate-pinnatifid, surfaces glabrous or sparsely pubescent, with simple trichomes 0.1-0.5 mm; sepals and distalmost cauline leaf blade surfaces glabrous. Boechera missouriensis
28 Basal leaf blade margins entire or dentate, surfaces pubescent, with simple and/or branched trichomes 0.4-1.7 mm; sepals and distalmost cauline leaf blade surfaces pubescent > 29
29 Biennials, caudices not evident; petals 3-5 mm; basal leaf blades 10-30 mm wide; fruiting pedicels horizontal; seeds with wings 0.4-1 mm wide distally. Boechera canadensis
29 Perennials (long-lived), caudices well-developed; petals 7-12 mm; basal leaf blades 0.5-7(-11) mm wide; fruiting pedicels ascending to divaricate-ascending; seeds with wings 0.1-0.2 mm wide distally > 30
30 Basal leaf blades 3-7(-11) mm wide, surfaces with 2-4-rayed trichomes; fruits 1.5-2.2 mm wide; seeds 1-1.2 mm wide. Boechera breweri
30 Basal leaf blades 0.5-2 mm wide, surfaces with simple and 2-rayed trichomes; fruits 2.3-3 mm wide; seeds 1.5-2 mm wide. Boechera cusickii
31 Biennials or perennials (short-lived), without woody caudices > 32
31 Perennials (long-lived), usually with woody caudices (except B. sparsiflora) > 39
32 Stems usually 2-5 per caudex branch, arising from margins of rosettes or laterally proximal to sterile shoots; cauline leaves 3-9, not concealing stems proximally; petals 4-7 mm > 33
32 Stems usually 1 per caudex branch, arising from centers of rosettes; cauline leaves (7-) 15-52, usually concealing stems proximally; petals 6-13 mm > 35
33 Basal leaf blade surfaces with 4-6(-8)-rayed trichomes; petals 6-7 mm; cauline leaf blades with auricles 1-3 mm; fruiting pedicels (7-)10-18 mm; seeds sub- biseriate; plants apomictic, pollen spheroid. Boechera gracilenta
33 Basal leaf blade surfaces with simple and 2- or 3-rayed trichomes; petals 4-6 mm; cauline leaf blades with auricles usually less than 1 mm; fruiting pedicels 5-10 mm; seeds uniseriate; plants sexual, pollen ellipsoid > 34
34 Distalmost cauline leaf blade surfaces glabrous; fruiting pedicels divaricate- ascending to horizontal, glabrous; nw Colorado, ne Utah Boechera glareosa
34 Distalmost cauline leaf blade surfaces pubescent; fruiting pedicels ascending, glabrous or sparsely pubescent; nc New Mexico. Boechera villosa
35 Basal leaf blade surfaces with sessile or subsessile branched trichomes > 36
35 Basal leaf blade surfaces with stalked branched trichomes > 37
36 Fruits (1.7-)2-2.5 mm wide; petals purple to lavender; fruiting pedicels 5-10(-12) mm; basal leaf blade surfaces with some 5- or 6-rayed trichomes. Boechera divaricarpa
36 Fruits 1-1.5(-1.8) mm wide; petals usually white; fruiting pedicels (5-) 8-30 mm; basal leaf blade surfaces with 2-4-rayed trichomes. Boechera grahamii
37 Fruiting pedicels with 2- or 3-rayed trichomes; fruits horizontal; petals 5-8 mm; plants apomictic, pollen spheroid. Boechera pauciflora
37 Fruiting pedicels glabrous or with predominantly simple trichomes; fruits usually ascending to divaricate-ascending, rarely horizontal; petals 7-13 mm; plants sexual, pollen ellipsoid > 38
38 Petals dark reddish purple (drying indigo), 1.5-2 mm wide; stems proximally sparsely pubescent, trichomes to 0.15 mm; ovules 80-100 per ovary. Boechera atrorubens
38 Petals purple to lavender or white, 2-5 mm wide; stems proximally densely pubescent, trichomes to 1.5 mm; ovules 90-170 per ovary. Boechera sparsiflora
39 Stems usually 2-5(-7) per caudex branch, arising from margins of rosettes > 40
39 Stems usually 1 per caudex branch, arising from centers of rosettes > 45
40 Fruits secund; ovules 20-32 per ovary; basal leaf blade surfaces with 2- or 3-rayed trichomes. Boechera pusilla
40 Fruits not secund; ovules 36-84 per ovary; basal leaf blade surfaces with 2-8-rayed trichomes > 41
41 Fruits 1.7-2 mm wide, usually strongly curved; seeds 1.5-2 × 1.1-1.5 mm. Boechera falcatoria
41 Fruits 0.8-1.5 mm wide, straight or slightly curved; seeds 1-1.5 × 0.7-1 mm > 42
42 Petals 0.5-0.8 mm wide; cauline leaves (5-)9-16; racemes 10-33 -flowered; plants apomictic, pollen spheroid. Boechera macounii
42 Petals 1-2 mm wide; cauline leaves 2-9; racemes 7-15-flowered; plants sexual, pollen ellipsoid > 43
43 Stems proximally with 2-4-rayed trichomes 0.08-0.3 mm; fruits horizontal; ovules 36-54 per ovary; (c Colorado). Boechera gunnisoniana
43 Stems proximally with simple and 2-rayed trichomes 0.3-0.6 mm; fruits usually ascending, rarely horizontal (B. glareosa); ovules 50-80 per ovary > 44
44 Basal leaf blade surfaces with simple and 2- or 3-rayed trichomes 0.3-0.5 mm; cauline leaf blades with auricles 0.3-0.6 mm. Boechera glareosa
44 Basal leaf blade surfaces with 4-8-rayed trichomes 0.05-0.1 mm; cauline leaf blades with auricles 0.5-1.5 mm. Boechera microphylla
45 Fruits 2.5-3.5 mm wide; seeds 2.5-3.2 × 1.8-2.5 mm. Boechera rigidissima
45 Fruits 0.8-2.2(-2.5) mm wide; seeds 1-2(-2.5) × 0.9-1.5 mm > 46
46 Fruits erect, appressed to rachises; ovules 24-40 per ovary. Boechera paupercula
46 Fruits ascending, divaricate, or horizontal, not appressed to rachises; ovules 46-250 per ovary > 47
47 Petals 0.5-2 mm wide; usually e of Sierra Nevada-Cascade crest > 48
47 Petals 2-5 mm wide; w of Sierra Nevada-Cascade crest (except B. sparsiflora) > 52
48 Basal leaf blade surfaces with trichomes 0.3-0.6 mm; fruits 1.5-2.2 mm wide; ovules 80-162 per ovary; cauline leaves (8-)14-60, blades with auricles (1-)3-10 mm. Boechera pauciflora
48 Basal leaf blade surfaces with trichomes 0.05-0.3 mm; fruits 0.8-1.5 mm wide; ovules 46-80 per ovary; cauline leaves 3-16, blades with auricles 0.5-1.5 mm > 49
49 Distal cauline leaf blades with surfaces pubescent; petals white; stems proximally with some 4- or 5-rayed trichomes; sc California. Boechera evadens
49 Distal cauline leaf blades with surfaces glabrous; petals lavender or purplish; stems proximally with simple and 2- or 3-rayed trichomes only; not sc California > 50
50 Fruits 0.8-1.2 mm wide; petals 0.5-0.8 mm wide; cauline leaves (5-)9-16; racemes 10-33-flowered. Boechera macounii
50 Fruits 1.2-1.5 mm wide; petals 1-1.8 mm wide; cauline leaves 2-6; racemes 3-15-flowered > 51
51 Stems proximally with trichomes simple and 2- or 3-rayed 0.1-0.2 mm; basal leaf blade surfaces with (2- or) 3-6-rayed trichomes usually 0.05-0.2(-0.3) mm; seeds with continuous wing; styles 0.8-1.5 mm; plants apomictic, pollen spheroid. Boechera cascadensis
51 Stems proximally with trichomes simple and 2-rayed 0.3-0.6 mm; basal leaf blade surfaces with some 7- or 8-rayed trichomes 0.05-0.1 mm; seeds with distal wing; styles 0.05-0.3 mm; plants sexual, pollen ellipsoid. Boechera microphylla
52 Fruiting pedicels with subappressed, 2-4-rayed trichomes. Boechera arcuata
52 Fruiting pedicels with spreading, simple and 2-rayed trichomes or glabrous > 53
53 Basal leaf blades 1-3 mm wide; caudices woody, with persistent, crowded, peg-like leaf bases. Boechera koehleri
53 Basal leaf blades 3-12 mm wide; caudices woody or not, without persistent, crowded, peg-like leaf bases > 54
54 Distal cauline leaf blades with glabrous surfaces (rarely margins ciliate); cauline leaf blades with auricles 3-10 mm; stems 3-8 dm; usually e of Sierra Nevada-Cascade axis. Boechera sparsiflora
54 Distal cauline leaf blades with pubescent surfaces; cauline leaf blades with auricles 0.5-3(-5) mm; stems 0.6-3.5(-4.5) dm; w of Sierra Nevada-Cascade axis > 55
55 Fruiting pedicels ascending to divaricate-ascending; basal leaf blade surfaces with trichomes 0.4-0.8 mm; petals 7-12 mm; plants sexual, pollen ellipsoid. Boechera breweri
55 Fruiting pedicels horizontal; basal leaf blade surfaces with trichomes 0.1-0.5 mm; petals 6-8 mm; plants apomictic, pollen spheroid. Boechera rubicundula