Small-head snakeweed

Brachyris microcephala de Candolle in A. P. de Candolle and A. L. P. P. de Candolle, Prodr. 5: 313. 1836; Gutierrezia sarothrae (Pursh) Britton & Rusby var. microcephala (de Candolle) L. D. Benson; Xanthocephalum microcephalum (de Candolle) Shinners

Subshrubs, 20–140 cm. Stems glabrous or minutely hispidulous. Leaves: basal and proximal absent at flowering; cauline blades 1-nerved, linear or filiform to narrowly oblanceolate or lanceolate, 0.5–2.2(–4) mm wide, little reduced distally. Heads (2–6, sessile to subsessile, in compact glomerules) in flat-topped arrays. Involucres cylindric, 1–1.5 mm diam. Phyllary apices flat. Ray florets 1(–2; each enclosed by conduplicate inner phyllary); corollas yellow, (1.5–)2–3.5 mm. Disc florets 1, sometimes 2 (functionally staminate; corollas broadly obdeltate-funnelform, throats widely flaring, lobes ¹ / 3 corolla lengths, recurved-coiling). Cypselae 1–1.8(–2.5) mm, faces densely strigoso-sericeous; pappi (rays, readily falling) of 1 series of narrowly lanceolate-oblong scales). 2n = 8, 16, 24, 32.

Flowering (Jun–)Jul–Dec(–Feb). Grasslands, chaparral, oak or oak-pine woodlands, usually over gravelly or rocky limestone or gypsum substrates, dunes; 800–2500 m; Ariz., Calif., Colo., Nev., N.Mex., Tex., Utah; Mexico (Baja California, Chihuahua, Coahuila, Durango, Nuevo León, San Luis Potosí, Sonora, Tamaulipas, Veracruz, Zacatecas).

Gutierrezia microcephala is recognized by its perennial habit and its small, tightly clustered heads, each with 4–8 phyllaries and 1(–2) ray and disc florets. Each ray floret is enclosed by a conduplicate inner phyllary. Forms of G. sarothrae with few florets in each head can be distinguished by their bisexual and fertile disc florets and tubular-funnelform disc corollas.