Ambrosia nivea (B. L. Rob. & Fern.) Payne

Franseria nivea Rob. & Fern. Proc. Am. Acad. 30: 117. 1895
Perennial, 3-10 dm. high; branches white-tomentose; leaves alternate, petioled, interruptedly pinnate; blades ovate in outline, white-tomentose on both sides, about 5 cm. long; upper part of the petioles and the rachis winged; principal divisions pinnately lobed and toothed, with small triangular ones interposed; staminate heads in terminal racemes; peduncles about 3 mm. long, recurved; involucre saucer-shaped or nearly rotate, white-tomentose, 4 mm. wide, with 9-10,short ovate lobes; paleae of the receptacle hyaline, clavate, 1-nerved; corolla with brownish angles and margins; pistillate heads in the upper axils and at the base of the staminate raceme, sessile, subtended by small leaves; fruit ovoid, 6-7 mm. long, cinereous, woody, 2-celled; beaks 2, stout, conic, 2 mm. long, somewhat curved but not hooked; spines 22-30, in 4 or 5 series, conic, scarcely curved, 1.5 mm. long.
Type locality: Plains near Casas Grandes, Chihuahua. Distribution: Known only from the type locality.