1. Athysanus pusillus (W. J. Hooker) Greene, Bull. Calif. Acad. Sci. 1: 72. 1885; Thysanocarpus pusillus W. J. Hooker, Icon. Pl. 1: plate 42. 1837. TYPE: United States, California, Monterey Co., Monterey, D. Douglas s.n. (holotype, K!; possible isotype, NY!).
Athysanus pusillus var. glabrior S. Watson in A. Gray & S. Watson, Syn. Fl. N. Amer. 1: 113. 1895. TYPE: United States, California, Fort Mohave, Apr 1884, J. G. Lemmon s.n. (holotype, GH!).
Thysanocarpus oblongifolius Nuttall in Torrey & A. Gray, Fl. N. Amer. 1: 118. 1838. TYPE: United States, Oregon, “rocky banks of the Oregon, near the junction of the Wahlamet,” Thomas Nuttall s.n. (holotype, GH!; isotypes, K!, PH!).
Herbs, sparsely to densely pubescent below, sometimes glabrous above. Stems (0.2–)0.5–3(–5) dm. Basal leaves with petioles 1–5 mm, oblanceolate, obovate, or oblong, entire or dentate, 3–15(–20) x (1–)2–6(–8) mm, uniformly pubescent with cruciform and 3-rayed trichomes, sometimes mixed adaxially with coarse simple trichomes, apex acute to obtuse; cauline leaves 1–6, about same size or smaller than basal leaves. Fruiting pedicels slender, (1.5–)2–4(–6) mm. Sepals oblong, 0.5–1 x 0.3–0.7 mm; petals white, oblong, 1.5–3 x 0.5–1 mm; filaments 0.4–0.6 mm; anthers (0.05–)0.1–0.2(–0.25) mm; ovules 2(–4) per ovary. Fruits orbicular to obovate, rarely broadly oblong, unilocular, not twisted, rounded or less frequently emarginate at apex, cuneate or obtuse at base; valves thin, sometimes with prominent veins, pubescent with simple, hooked trichomes to 0.5 mm, these sometimes restricted to fruit margin or frequently mixed with much smaller, sessile cruciform or 3-rayed trichomes, rarely fruits glabrous; septum absent; style 0.05–0.2 mm. Seeds 1, brown, (0.8–)0.9–1.1(–1.2) x (0.5–)0.7–0.9(–1) mm. 2n = 26.
Habitat: open grassy slopes, grassy glades in woodlands, chaparral, sandy and gravelly flats, flood plains, rock outcrops, cliffs and ledges, on limestone, serpentine, sandstone, granitic and basaltic substrates.
Elevation: 0–1800 m.
Distribution: Canada (S British Columbia), Mexico (Baja California), United States (Arizona, California, Idaho, Montana, Nevada, Oregon, Washington).