Arabis modesta
Arabis nuttallii
modest rock-cress, Rogue Canyon rock-cress
Nuttall's rockcress
simple or few from base (caudex), erect, usually unbranched, rarely branched (few) distally, 2.2–5.5(–6.7) dm, (usually pubescent throughout, rarely subglabrate distally, trichomes stellate).
simple or few to numerous from base (caudex), erect or ascending, unbranched, 0.5–2.5(–3.6) dm, (glabrous throughout or pubescent along proximal 1/2, trichomes simple).
petiole 1–4(–5) cm, (rarely minutely ciliate near base);
blade oblanceolate to obovate, (0.8–)2–4.5(–6) cm × (4–)10–20(–25) mm, margins entire, repand, or dentate, (not ciliate), apex obtuse, surfaces pubescent, trichomes short-stalked, stellate.
petiole 0.3–2(–3.5) cm, (glabrous or ciliate);
blade narrowly oblanceolate, spatulate, to obovate, 0.4–2(–3) cm × 3–10(–15) mm, margins entire, (ciliate or not), apex obtuse, surfaces glabrous or sparsely to densely pubescent, trichomes simple, rarely mixed with forked ones.
(2–)4–6(–9);
blade oblong or ovate, 1–3.5(–4.5) cm × (3–)6–10(–20) mm, base not auriculate, margins entire, repand, or dentate, apex obtuse or acute, surfaces pubescent, trichomes short-stalked, stellate.
(1 or) 2–5(–7);
blade linear, oblanceolate, oblong, or obovate, 0.5–2.2(–3) cm × 2–8(–12) mm, base not auriculate, margins entire, (sometimes ciliate), apex obtuse, surfaces glabrous or, rarely, sparsely pubescent.
simple, (dense).
simple, (dense or lax).
sepals (purple), oblong, (4–)5–6.5(–8) × 1.5–2 mm, lateral pair saccate basally;
petals purple, spatulate, (10–)12–16(–20) × 4–6(–7) mm, apex rounded;
filaments (4–)5–8 mm;
anthers narrowly oblong, 1.3–2 mm.
sepals (greenish) oblong, 2.5–3.5 × 1.2–1.5 mm, lateral pair saccate basally, (glabrous);
petals white, oblanceolate to spatulate, (5–)6–8 × 2–4 mm, apex rounded;
filaments 2.5–4 mm;
anthers oblong, 0.6–1 mm.
ascending to divaricate, 7–18(–25) mm.
ascending to divaricate, (2–)5–20(–30) mm, (glabrous).
suberect to divaricate, sometimes slightly curved, slightly torulose, (2.8–)3.5–6 cm × 1.5–2 mm;
valves each with prominent midvein extending to middle or full length;
ovules 20–34 per ovary;
style 0.5–1(–1.5) mm.
ascending to suberect, (not appressed to rachis), slightly torulose, sometimes slightly curved, (0.7–)1–2.5(–2.8) cm × 0.8–1.2(–1.5) mm;
valves each with distinct midvein extending full length;
ovules 10–24 per ovary;
style 0.5–1.2(–2) mm, (slender).
winged distally, oblong, 1.7–2.2 × 0.9–1.2 mm;
wing 0.2–0.5 mm wide.
not winged, broadly ovate, 0.6–1.2(–1.5) × 0.5–1 mm.
= 32.
= 32.
Arabis modesta
Arabis nuttallii
Arabis modesta, known only from Napa, Siskiyou, and Yolo counties (California), and Jackson and Josephine counties (Oregon), and the following four species form a well-defined group easily separated from the first nine species above by their large, purple petals. Arabis modesta is readily distinguished from other purple-flowered Arabis by having very fine, short-stalked cruciform and 3-rayed, instead of simple and 2-rayed, forked trichomes. Arabis blepharophylla has broadly winged, orbicular seeds, and the other purple-flowered species (A. aculeolata, A. mcdonaldiana, A. oregana) have oblong seeds that are not winged or narrowly winged distally. The lines separating these three species are not as well-defined as those of A. blepharophylla and A. modesta, and further studies are needed to resolve them. I prefer to maintain all five species of purple-flowered Arabis as distinct until thorough molecular and hybridization studies are conducted. In the absence of such studies, it is unwise to make any nomenclatural changes.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Arabis nuttallii, the second most widespread native North American species of the genus, is variable in density of indumentum, types of trichomes, plant height, pedicel length, fruit width, leaf shape, flowering and fruiting time, and elevation. As indicated by R. C. Rollins (1941, 1993), the variation seems to be sporadic and does not correlate with clear-cut entities and, therefore, the species cannot be subdivided meaningfully.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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