South Texas ambrosia
Perennials or subshrubs, 10-30+ cm (rhizomatous and/or soboliferous, colonial). Stems erect. Leaves opposite (distal sometimes alternate); petioles 0; blades lanceolate or lance-elliptic to lance-oblong or oblanceolate, 20-50(-70+) × 8-12(-25+) mm, rarely ± pinnately lobed (lobes ± deltate), bases cuneate (then rounded), margins entire or toothed, abaxial faces densely strigose (silvery gray), adaxial faces strigillose. Pistillate heads clustered (in axils), proximal to staminates; florets 1(-2). Staminate heads: peduncles 1-4+ mm; involucres cup-shaped (sometimes with black nerve in each lobe), 3-4+ mm diam., strigillose; florets 8-18+. Burs: bodies ± pyriform to ± globose, 2-3+ mm, glabrous or strigose, spines (1-)3-5+, scattered, stoutly conic, 0.4-0.8+ mm, tips straight (often each with black nerve). 2n = 72. Flowering Jun-Nov. Seasonally wet clays or sands, scrublands; 10-30+ m; Tex.; Mexico (Tamaulipas).
This project made possible by National Science Foundation Award 1410069