Boechera pygmaea |
Boechera divaricarpa |
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Tulare County rock cress |
spreading-pod rock-cress, uplifting suncress |
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Habit | Perennials; usually long-lived; sexual; caudex woody, (often with persistent, crowded leaf bases). | Biennials or perennials; short-lived; apomictic; caudex present or absent. |
Stems | usually 2–5 per caudex branch, arising from margin of rosette near ground surface, or arising laterally proximal to sterile shoots, 0.2–0.8 dm, pubescent proximally, trichomes simple and short-stalked, 2- or 3-rayed, to 0.4 mm, glabrescent distally. |
usually 1 per caudex branch, arising from center of rosette near ground surface, (1.5–)3–9 dm, glabrous or pubescent proximally, trichomes sessile, 2–4-rayed (some simple), to 0.7 mm, glabrous distally. |
Basal leaves | blade linear, 0.8–1.5 mm wide, margins entire, ciliate, trichomes (simple and spurred), to 0.8 mm, surfaces moderately pubescent, trichomes short-stalked, 2–4-rayed, 0.05–0.4 mm. |
blade oblanceolate, 2–10 mm wide, margins usually entire, rarely denticulate, ciliate along petiole, trichomes (simple), to 0.8 mm, surfaces sparsely to densely pubescent, trichomes sessile, 2–6-rayed, 0.1–0.4 mm. |
Cauline leaves | 2–4, not concealing stem; blade auricles absent, surfaces of distalmost leaves pubescent. |
(10–)15–56, concealing stem proximally; blade auricles 1–5 mm, surfaces of distalmost leaves glabrous. |
Racemes | 2–5-flowered, unbranched. |
12–40(–65)-flowered, usually unbranched. |
Flowers | erect at anthesis; sepals pubescent; petals white, 3.5–5 × 0.7–1 mm, glabrous; pollen ellipsoid. |
divaricate-ascending at anthesis; sepals glabrous or with scattered trichomes; petals usually purple, rarely lavender, 6–9 × 1.5–3 mm, glabrous; pollen spheroid. |
Fruiting pedicels | erect to ascending, straight, 2–7 mm, usually pubescent, rarely glabrous, trichomes subappressed, branched. |
divaricate-ascending to horizontal, straight, 5–12 mm, glabrous. |
Fruits | erect to ascending, often appressed to rachis, not secund, straight, edges parallel, (1.3–)2–3.3 cm × 4–5 mm; valves glabrous; ovules 8–12 per ovary; style 0.05–0.4 mm. |
divaricate-ascending to horizontal, not appressed to rachis, not secund, straight, edges parallel, (4.5–)5.5–11 cm × 1.7–2.5 mm; valves glabrous; ovules 114–142 per ovary; style 0.05–0.2 mm. |
Seeds | uniseriate, 3–5 × 2.5–4.5 mm; wing continuous, 0.8–2 mm wide distally. |
uniseriate to sub-biseriate, 1.4–2 × 1–1.5 mm; wing continuous, 0.1–0.2 mm wide. |
2n | = 21. |
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Boechera pygmaea |
Boechera divaricarpa |
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Phenology | Flowering May–Jul. | Flowering May–Jul. |
Habitat | Barren flats of arkosic gravel | Rock outcrops, talus slopes and gravelly hillsides in sagebrush, mountain shrub, and open conifer forests |
Elevation | 2400-3200 m (7900-10500 ft) | 900-2500 m (3000-8200 ft) |
Distribution |
CA |
CA; ID; MT; NV; UT; WA; WY
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Discussion | Of conservation concern. Despite the distinctive morphology of Boechera pygmaea, there is evidence that it is capable of producing fertile hybrids with B. stricta. It is known only from Inyo and Tulare counties in the southern Sierra Nevada. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
The name Arabis (Boechera) divaricarpa has been applied to nearly every hybrid containing a genome derived from B. stricta. This presents a serious barrier to understanding the evolution of Boechera and also is contrary to the International Code of Botanical Nomenclature, because some names usually placed in synonymy (i.e., B. grahamii and B. brachycarpa) have priority at species level (M. D. Windham and I. A. Al-Shehbaz 2007b). To address this problem, we treat the following as distinct species: B. acutina, B. grahamii (= B. brachycarpa of R. D. Dorn 2001), and B. pratincola (all considered synonyms of A. divaricarpa by R. C. Rollins 1993), and B. calderi, B. elkoensis, and B. quebecensis (taxa described after 1993). Detailed comparison among these taxa are provided by Windham and Al-Shehbaz (2007, 2007b). The narrow concept of B. divaricarpa advocated here encompasses apomictic triploid populations containing three distinct genomes, one each derived from B. retrofracta, B. sparsiflora, and B. stricta. If the species is defined more broadly, the name B. grahamii has priority. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 7, p. 401. | FNA vol. 7, p. 374. |
Parent taxa | ||
Sibling taxa | ||
Synonyms | Arabis pygmaea | Arabis divaricarpa, Arabis stokesiae |
Name authority | (Rollins) Al-Shehbaz: Novon 13: 388. (2003) | (A. Nelson) Á. Löve & D. Löve: Bot. Not. 128: 513. (1976) |
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