Arabis |
Arabis aculeolata |
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rock-cress |
Waldo rock-cress |
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Habit | Annuals, biennials, or perennials; (sometimes stoloniferous with vegetative rosettes, or caudex simple or branched); not scapose; often pubescent or hirsute, sometimes glabrous or glabrate, trichomes stalked, stellate, sometimes mixed with fewer, simple or forked ones. | Perennials; (caudex simple or branched, covered with persistent petiolar remains); sparsely to moderately pubescent, trichomes sub-setiform, bulbous-based, simple, (to 1.5 mm), often mixed with fewer, forked, stalked ones. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Stems | erect, ascending, or decumbent, unbranched or branched distally. |
simple or few from base (caudex), erect, unbranched, (0.6–)1.5–3.5(–4.5) dm, (sparsely to densely hirsute basally or throughout). |
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Leaves | basal and cauline; petiolate or sessile; basal rosulate, petiolate or sessile, blade margins usually entire or dentate to denticulate, rarely lyrate-pinnatifid; cauline usually sessile, rarely shortly petiolate, blade (base often auriculate, sagittate, or amplexicaul), margins entire or dentate. |
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Basal leaves | petiole 0.3–1.5 cm, (ciliate); blade oblanceolate to obovate, (0.5–)1–3(–4) cm × (2–)3–6(–10) mm, margins entire, repand, or obtusely dentate, (ciliate), apex obtuse, surfaces pubescent, trichomes usually simple, sometimes mixed with fewer forked ones, rarely subglabrate. |
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Cauline leaves | 3–6 (or 7); blade oblong, 0.4–1(–1.5) cm × (1–)2–4 mm, base not auriculate, margins entire or repand, apex obtuse. |
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Racemes | (sometimes paniculate, usually simple, sometimes branched). |
simple, (dense). |
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Flowers | sepals erect or ascending, ovate or oblong, lateral pair saccate or not basally, (margins membranous); petals white, pink, or purple, usually spatulate, oblong, or oblanceolate, rarely obovate, claw differentiated from blade, (shorter than sepals, apex obtuse or rounded); stamens tetradynamous; filaments usually not dilated basally; anthers ovate, oblong, or linear, (apex obtuse); nectar glands confluent, subtending bases of stamens, lateral glands semiannular or annular, median glands rarely absent, (sometimes toothlike and distinct). |
sepals (purple), oblong, 4–8 × 1.5–2.5 mm, lateral pair saccate basally; petals purple, spatulate, (9–)10–18(–20) × (2.5–)3.5–6(–8) mm, apex obtuse; filaments 4–9 mm; anthers oblong, 1.5–2 mm. |
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Fruiting pedicels | erect, ascending, or divaricate, (not reflexed or secund), slender. |
ascending to suberect, 8–12(–15) mm, (subglabrate or sparsely pubescent). |
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Fruits | siliques, usually sessile, rarely shortly stipitate, linear, smooth or torulose, (usually straight, sometimes slightly curved), flattened, latiseptate; valves (papery), each with obscure or prominent midvein, glabrous; replum (visible), rounded; septum complete, (membranous, translucent, veinless); ovules 10–86[–110] per ovary; style obsolete or distinct; stigma capitate, (sometimes slightly 2-lobed). |
ascending to suberect, not torulose, sometimes slightly curved, 3.5–6.5 cm × 1.5–2 mm; valves each with prominent midvein extending full length; ovules 24–36 per ovary; style (0.7–)1–2 mm. |
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Seeds | uniseriate, flattened, winged or margined, oblong or orbicular; seed coat (smooth or minutely reticulate), not mucilaginous when wetted; cotyledons accumbent. |
narrowly winged nearly throughout except wider distally, oblong, 1.5–2.3 × 1–1.3 mm; wing 0.1–0.3 mm wide. |
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x | = 8. |
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2n | = 32. |
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Arabis |
Arabis aculeolata |
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Phenology | Flowering Mar–May(-Jun). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Habitat | Serpentine slopes, rocky hillsides | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Elevation | 200-1800 m (700-5900 ft) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Distribution |
North America; Europe; Asia; n, alpine; c Africa; e Africa |
OR
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Discussion | Species ca. 70 (15 in the flora). As treated by most North American authors (e.g., M. Hopkins 1937; R. C. Rollins 1941, 1993; G. A. Mulligan 1996), Arabis was so broadly delimited that it included species presently assigned to six genera in five tribes (I. A. Al-Shehbaz et al. 2006). These are: Arabidopsis and Turritis (Camelineae), Arabis (Arabideae), Boechera (Boechereae), Pennellia (Halimolobeae), and Streptanthus (Thelypodieae) (see Al-Shehbaz 2003b; M. D. Windham and Al-Shehbaz 2006, 2007). R. C. Rollins (1993) recognized 80 species of Arabis in North America, of which 24 were divided into 40 varieties. By contrast, G. A. Mulligan (1996) recognized 30 species and six varieties in Canada alone. The combination of characteristics that they used to circumscribe the genus (e.g., linear and latiseptate fruits, accumbent cotyledons, and often branched trichomes) evolved repeatedly in Brassicaceae and cannot be relied on in the delimitation of genera (O. Appel and I. A. Al-Shehbaz 2003). The vast majority of North American species have been transferred to Boechera (x = 7), a genus distinct morphologically, cytologically, and molecularly (Al-Shehbaz 2003b; M. D. Windham and Al-Shehbaz 2006, 2007, 2007b). As currently circumscribed, Arabis (x = 8) is a primarily Eurasian genus with only 15 species in North America. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Arabis aculeolata is known only from Curry, Douglas, and Josephine counties. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 7, p. 257. | FNA vol. 7, p. 265. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Name authority | Linnaeus: Sp. Pl. 2: 664. (1753): Gen. Pl. ed. 5, 298. (1754) | Greene: Leafl. Bot. Observ. Crit. 2: 69. (1910) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Web links |