Proc. Amer. Acad. Arts 8: 633. 1873.
Plants 2–6 cm. Stems simple or branched, rarely with many branches from bases. Leaf blades linear to filiform, 12–32 × 0.5–1 mm. Involucres turbinate to campanulate. Phyllaries in 2(–3) series, elliptic to obovate, glabrous or sparsely and minutely glandular. Ray (or pistillate) florets 0 or 1–5; corollas white, laminae 0.8–2 mm, or 0, or apiculum 0.1–0.5(–1) mm. Disc florets 3–6(–15); corollas yellowish to reddish, club-shaped, widened through limbs, abruptly contracted at lobes, lobes 5, (lobes and sometimes distalmost portion of limbs) yellow or purplish red at maturity, style branches (0.7–)1–2 mm, stigmatic portions 0.4–0.5 mm. Pappi 0, or of (3–)5 bristles, not dilated at bases. 2n = 18.
Subspecies 2 (2 in the flora).
Plants of Pentachaeta exilis with greatly reduced or completely absent pappi apparently are scattered over the range of the species. This feature is relatively constant within a population.
|1||Ray (pistillate) corollas elaminate or with apiculum 0.1–0.5(–1) mm; disc florets 3–6(–15), corolla lobes red-purple, style branches (0.7–)1–2 mm, stigmatic portions 0.4–0.5 mm||Pentachaeta exilis subsp. exilis|
|1||Ray (pistillate) corollas laminate, laminae 0.8–2 mm; disc florets (7–)15–34, corolla lobes yellow, style branches 2–3 mm, stigmatic portions 0.6–1mm||Pentachaeta exilis subsp. aeolica|