1a. Guilleminea densa (Humboldt & Bonpland ex Schultes) Moquin-Tandon var. aggregata Uline & W. L. Bray, Bot. Gaz. 20: 343. 1895.
Plants 1-8 dm diam. Stems procumbent, 0.5-1.5 mm diam., villous to densely woolly-villous. Leaves basal and cauline; basal rosette leaves with winged petiole 8-20 mm, blade oblong-elliptic to lanceolate, (8-)20-40 × (1-)6-9 (-13) mm, glabrous adaxially, villous abaxially; cauline leaves with petiole 2-4 mm, blade broadly to narrowly ovate, oblong-ovate, oblong, rhombic, or occasionally elliptic to lanceolate, 2-10(-23) × 2-8(-14) cm, glabrous adaxially, villous to woolly-villous abaxially. Inflorescences white, 2-3 × 3-5 mm. Flowers sessile; calyx tubes 0.8-1.2 mm; tepal lobes whitish, ovate to elliptic, 0.8-1.5 mm, membranaceous, apex acute to rounded, abaxially villous (at least near base). Utricles included within tepals, 1.1-1.4 mm. Seeds 0.8-0.9 × 0.6-0.7 mm.
Flowering spring-fall. Dry sandy, gravelly, sandstone areas, waste places; (0-)1200-2600 m; Ariz., Calif., Colo., N.Mex., Okla., Tex.; Mexico.
Guilleminea densa var. aggregata has been reported also from Maryland and South Carolina; I have seen no specimens to support those reports.