Contr. Gray Herb. 206: 12. 1976.
Annuals; (often glaucous), glabrous throughout. Stems unbranched or branched distally, 3–10 dm. Basal leaves (soon withered); not rosulate; blade oblong to lanceolate or oblanceolate, 3–6 cm × 5–15 mm, margins usually entire, rarely denticulate. Cauline leaves sessile; blade (proximalmost) oblong to lanceolate or oblanceolate, or (distal) linear to narrowly oblong or lanceolate, base auriculate, margins usually entire, rarely denticulate. Racemes lax. Fruiting pedicels horizontal to divaricate, straight or slightly recurved, (slender), 7–15 mm. Flowers: sepals spreading, whitish or purplish, 1.8–2.5 × 0.7–1 mm; petals white, obovate to spatulate, 2.5–4.5 × 1.7–2.5 mm, claw 1–1.5 mm; median filament pairs 1.7–2.5 mm; anthers ovate, 0.5–0.8 mm; gynophore 0.2–0.4 mm. Fruits erect to ascending, straight or curved, strongly torulose, 1.5–2.5 cm × 1–1.2 mm; ovules 20–32 per ovary; style cylindrical, 0.5–0.8 mm; stigma obscurely 2-lobed. Seeds 1–1.5 × 0.7–0.9 mm. 2n = 20.
Phenology: Flowering Jul–Aug.
Habitat: Open wooded slopes, mixed coniferous forests, canyons
Elevation: 1900-2500 m
Thelypodiopsis vaseyi is known from Lincoln, Otero, and San Miguel counties in New Mexico and Culberson County in Texas. R. C. Rollins (1982b, 1993) did not record it from Texas; the first report from there is based on Johnston 3148 (MO), collected in Guadalupe Mountains. Sisymbrium watsonii Payson is an illegitimate name that pertains to S. vaseyi.