Erysimum capitatum var. purshii

Proximal leaves with mostly 2- or 3-rayed trichomes adaxially. Flowers: petals usually yellow, rarely lavender or purplish. Fruits usually 4-angled, rarely latiseptate. Seeds 1.5-2(-2.4) × 0.7-1.2 mm; not winged. 2n = 36.

Flowering Apr-Sep. Meadows, dry slopes, hillsides; 1000-3800 m; Yukon; Alaska, Ariz., Calif., Colo., Idaho, Mont., Nev., N.Mex., Tex., Utah, Wyo.; Mexico (Chihuahua, Michoacán, Sonora, Zacatecas).

Plants of var. purshii were placed by G. B. Rossbach (1958) in three species (Erysimum angustatum, E. argillosum, E. desertorum) and by R. C. Rollins (1993) in two species (E. angustatum, E. capitatum). The considerable overlap in morphology and the frequent hybridization between vars. capitatum and purshii in areas where their geographical ranges meet argue against such delimitation. Forms with linear leaves to 3 mm wide, which are restricted to eastern Alaska and western Yukon, were recognized by Rossbach and Rollins as E. angustatum, but these hardly differ from typical var. purshii in all other characters.