Annuals, rarely biennials; taproots 2–10+ cm. Stems 1–3, usually branched in distal 1/2, sometimes throughout, moderately stout to stout, not wiry, mostly glabrous. Leaves: basal (if persisting) 50–80 × 15–25 mm, pinnatifid, rarely 2-pinnatifid; cauline evenly spaced, proximal often spatulate, distal 2/3 narrowly to broadly lanceolate, 5–35 × 8–12 mm, markedly reduced distally, margins of proximal pinnatifid to coarsely serrate, of distal minutely, evenly serrulate or entire and antrorsely ciliolate, teeth or cilia 50–90+ per side, teeth tipped by white seta 0.1–1.5 mm, faces glabrous. Peduncles moderately to densely hispidulous, eglandular; usually ebracteate. Involucres hemispheric, 5–10 × 11–20 mm. Phyllaries in 3–4 series, faces glabrous; outer usually 1.5–8.5 × 2–5 mm, ciliate; inner 2–10.5 × 1.5–4 mm, often ciliate. Ray florets 12–34; corollas yellow, tubes 2.5–3 mm, laminae 5–18 × 2–3 mm. Disc florets 50–200+; corollas 4.5–5 mm. Cypselae 1.6–1.8 mm; pappi 5–6.5 mm, outer lengths often 0.5 longest.
Varieties 3 (3 in the flora).
The polymorphic Xanthisma texanum has always been kept distinct from other genera in the tribe, in part due to the unique involucre, here considered a derived structure. The relationship to members of Machaeranthera in the broad sense was never considered until DNA data became available. According to J. C. Semple (1974), the following combination of features characterizes the species: “heterocarpic fruit with a pappus of bristly scales only, fruit pubescence of long white ascending hairs, receptacle slightly convex with a persistent reticulate network of subulate scales.” Interestingly, all of these characters are found in at least some of the taxa of the newly expanded genus.
J. C. Semple (1974) classified varieties texanum and orientale under the typical subspecies (as they are peripherally sympatric and appear to hybridize) and the allopatric X. texanum var. drummondii at the subspecific level. The three taxa are here treated as varieties.
|1||Phyllaries abruptly expanded distal to stalks; bodies mostly ovate (3.5–8 × 2.5–5 mm distal to widest point)||Xanthisma texanum var. drummondii|
|1||Phyllaries somewhat expanded distally; bodies mostly orbiculate to depressed-elliptic (1–2 × 1.5–3.5 mm distal to widest point)||> 2|
|2||Phyllary apices rounded, with little or no flare 1 mm from tip||Xanthisma texanum var. texanum|
|2||Phyllary apices obtusely cuspidate, flareddistally, ovate portion 1.5–2 × 2–3 mm (distal to widest point)||Xanthisma texanum var. orientale|