Thelypodium ambiguum S. Watson, Proc. Amer. Acad. Arts 14: 290. 1879; Sisymbrium ambiguum (S. Watson) Payson; Thelypodiopsis ambigua var. erecta Rollins

Annuals or biennials; (glaucous), glabrous throughout. Stems branched distally, (3-)5-10 dm. Basal leaves rosulate; petiole 0.3-3 cm; blade oblanceolate, (1.5-)2.5-14.5(-20) cm × 10-30(-42) mm, margins dentate to subpinnatifid. Cauline leaves sessile; blade lanceolate to oblong, base auriculate, margins usually entire, rarely dentate. Racemes lax or dense. Fruiting pedicels horizontal to divaricate-ascending, often upcurved, 6-9 mm. Flowers: sepals erect, purple, 5-7.5 × 1.7-2.5 mm; petals purple to lavender or white, spatulate, 10-14 × 1.2-1.7 mm, claw 4-6 mm; median filament pairs 4-6 mm; anthers linear, 3-4 mm; gynophore (slender), 3-6(-9.5) mm. Fruits ascending to divaricate or descending, straight or slightly recurved, torulose, 4.5-9 cm × 1.1-1.4 mm; ovules 80-112 per ovary; style cylindrical, (stout), 0.3-1 mm; stigma 2-lobed. Seeds 1.2-1.5 × 0.8-1.2 mm. 2n = 22.

Flowering Mar-Jun. Pinyon-juniper desert shrub communities, dry hillsides; of conservation concern; 800-1600 m; Ariz., Utah.

Thelypodiopsis ambigua is known from Kane County in Utah and from Coconino, Mohave, and Yavapai counties in Arizona.