Big-head rabbit-tobacco

Evax prolifera Nuttall ex de Candolle in A. P. de Candolle and A. L. P. P. de Candolle, Prodr. 5: 459. 1836

Plants grayish green to silvery, 3–15 cm, sericeous to lanuginose. Stems mostly 2–10; branches proximal and distal (distal opposite or, sometimes, appearing alternate when unequal), rarely none. Leaves: largest 7–15 × 2–4 mm; capitular leaves subtending glomerules, also visible between and surpassing heads. Heads in strictly dichasiform or pseudo-polytomous arrays (sometimes appearing monochasiiform), cylindric to ± ellipsoid, 3.5–4.5 mm, heights 2–3 times diams. Receptacles broadly or narrowly conic, 0.4–0.6 mm or ± 0.9–1.1 mm, heights 0.5–0.7 or 2–2.4 times diams. Pistillate paleae imbricate, longest 2.5–4 mm. Staminate paleae ± 3, apices erect to somewhat spreading, ± plane. Functionally staminate florets 2–4; ovaries partly developed, 0.4–0.6 mm; corollas hidden in heads, actinomorphic, 1.4–2 mm, glabrous, lobes equal. Bisexual florets 0. Cypselae ± angular, obcompressed, mostly 0.9–1.2 mm.

Varieties 2 (2 in the flora): sw United States.

Intermediates between the two varieties of Diaperia prolifera occur where their ranges meet in central Texas and central Oklahoma. The strictly dichasiform or pseudo-polytomous branching pattern of D. prolifera is distinctive and diagnostic within the genus. Specimens of D. prolifera from introductions around a wool mill in South Carolina (G. L. Nesom 2004c, as Evax prolifera) are as yet undetermined to variety and are not included in the distributions below.