Boechera saximontana |
Boechera horizontalis |
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Crater Lake rock-cress |
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Habit | Perennials; short-lived; apomictic; caudex usually not woody. | Perennials; long-lived; (cespitose); apomictic; caudex woody. |
Stems | usually 1 per caudex branch, arising from center of rosette near ground surface, 0.7–3 dm, densely pubescent proximally, trichomes short-stalked, 2–6-rayed, 0.06–0.25 mm, glabrous distally. |
usually 1 per caudex branch, arising from center of rosette, near ground surface or somewhat elevated on woody base, or 1–3.5 dm, sparsely pubescent proximally, trichomes short-stalked, 3–6-rayed, 0.1–0.3 mm, glabrous distally. |
Basal leaves | blade narrowly oblanceolate, 1–3 mm wide, margins entire, ciliate near petiole base, trichomes (simple and spurred), to 0.4 mm, surfaces sparsely to densely pubescent, trichomes short-stalked, 4–8-rayed, 0.04–0.15 mm. |
blade narrowly oblanceolate, 1–5 mm wide, margins entire, ciliate near petiole base, trichomes (simple), to 0.4 mm, surfaces densely pubescent, trichomes short-stalked, 3–6-rayed, 0.1–0.3 mm. |
Cauline leaves | 5–9, rarely concealing stem proximally; blade auricles to 0.3–1 mm, surfaces of distalmost leaves glabrous. |
3–13, often concealing stem proximally; blade auricles 0.5–1.5 mm, surfaces of distalmost leaves glabrous. |
Racemes | 5–13-flowered, usually unbranched. |
5–32-flowered, usually unbranched. |
Flowers | ascending at anthesis; sepals pubescent; petals lavender, 4–5 × 0.5–0.8 mm, glabrous; pollen spheroid. |
divaricate-ascending at anthesis; sepals pubescent; petals lavender to purple, 5–6 × 1.5–2 mm, glabrous; pollen spheroid. |
Fruiting pedicels | divaricate-ascending, straight, 3–8 mm, glabrous. |
horizontal to descending, straight or slightly curved downward, 4–11 mm, glabrous. |
Fruits | divaricate-ascending, not appressed to rachis, not secund, straight, edges parallel, (2.5–)3–4.7 cm × 1.2–1.7 mm; valves glabrous; ovules 78–112 per ovary; style 0.1–0.5 mm. |
horizontal or descending, not appressed to rachis, secund, straight, edges slightly undulate (not parallel), 2–4 cm × 2–3 mm; valves glabrous; ovules 40–54 per ovary; style 0.2–0.5 mm. |
Seeds | uniseriate to sub-biseriate, 1.1–1.4 × 0.7–0.9 mm; wing continuous, 0.05–0.12 mm wide. |
uniseriate, 2–2.5 × 1.7–2 mm; wing continuous, 0.5–1 mm wide. |
Boechera saximontana |
Boechera horizontalis |
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Phenology | Flowering Jun–Jul. | Flowering Jul–Aug. |
Habitat | Rocky soil in sagebrush and open conifer forests | Dry pumice slopes |
Elevation | 2400-2900 m (7900-9500 ft) | |
Distribution |
ID; WY |
OR |
Discussion | Boechera saximontana is an apomictic taxon that has been treated as a variety of either Arabis microphylla (R. C. Rollins 1941) or A. (Boechera) williamsii (Rollins 1993; R. D. Dorn 2001). It is easily distinguished from typical collections of those species (see M. D. Windham and I. A. Al-Shehbaz 2007b for detailed comparison), but it is likely that one (or both) were involved in its hybrid origin. It is known from Blaine, Custer, and Lemhi counties in Idaho, and Big Horn and Fremont counties in Wyoming. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Morphological evidence suggests that Boechera horizontalis is an apomictic species that arose through hybridization between B. lemmonii and B. suffrutescens (M. D. Windham and I. A. Al-Shehbaz 2007). Boechera horizontalis is known only from the vicinity of Crater Lake in south-central Oregon. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 7, p. 404. | FNA vol. 7, p. 384. |
Parent taxa | ||
Sibling taxa | ||
Synonyms | Arabis microphylla var. saximontana, Arabis pendulocarpa var. saximontana, Arabis williamsii var. saximontana, B. williamsii var. saximontana | Arabis horizontalis, Arabis suffrutescens var. horizontalis |
Name authority | (Rollins) Windham & Al-Shehbaz: Harvard Pap. Bot. 12: 248. (2007) | (Greene) Windham & Al-Shehbaz: Harvard Pap. Bot. 11: 266. (2007) |
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