Orthocarpus purpureo-albus is a middle elevation herb with a single stem at the base, then dividing higher up. It lives in middle elevation meadows and moist fields and seems to prefer Artemisia as a host, as do plants in the genus Orobanche here. The flowers are a combination of purple and white. The leaves are either entire or three fingered with linear segments.
General: Annual, semi-parasitic, 10-40 cm tall; stems erect, simple to usually branched above, often purplish; herbage glandular-puberulent; taprooted. Leaves: Cauline, alternate, linear to filiform (often the lowermost blades) or 3-cleft with filiform segments, 1.5- 3.5 cm long, the ultimate margins entire; blades sessile. Flowers: Solitary in the leaf axils; pedicels 0.7-2.2 cm long; calyx tubular, 4-7 mm long, elongating in fruit, ribs reddish, lobes subequal, broadly ovate, the tips rounded, ciliate; corolla soon deciduous after flowering, 6-10 mm long, yellow with maroon dots, or sometimes pinkish to purplish, weakly bilabiate, the top of the lower lip puberulent; flowers March-June. Fruits: Loculicidal capsule, narrowly elliptical, 6-7.5 mm long; seeds few, the surface deeply net-veined. Ecology: Sagebrush habitats, pinyon-juniper woodlands, coniferous forests; 1400-2700 m (4500-9000 ft); Apache, Coconino, Mohave, Navajo, and Yavapai counties; southwestern U.S. Notes: Orthocarpus spp. appear very similar vegetatively to Castilleja spp. Orthocarpus luteus (yellow owl-clover) is differentiated by simple to rarely branched stems; corolla is yellow, and the galea is equal in length to the lower lip, the apex not hooked. It occurs in similar habitats. Rhinanthus minor (yellow rattle) [=R. rigidus] is an annual, 20-70 cm tall; stems are simple to branched, often pilose in longitudinal lines; leaves are opposite, sessile, lanceolate to linear, 2-6 cm long, scabrous, the margins sharply serrate; inflorescence is a spike-like raceme; calyx is 4-toothed, becoming inflated and bladder-like in fruit, 12-17 mm long; corolla is 7-14 mm long, yellow, bilabiate, the upper lip arched, the lower lip shorter with 3 spreading lobes; fruit is a loculicidal capsule, orbicular, compressed, with several seeds. It occurs uncommonly in meadows, valleys, and wooded slopes in eastern Arizona. The Navajo use O. purpureo-albus as a cathartic, and a cold tea is used to treat heartburn. Editor: Springer et al. 2008