Mesa tansyaster

Aster tagetinus (Greene) S. F. Blake; Machaeranthera humilis (A. Gray) Standley; M. tanacetifolia Kunth var. humilis A. Gray

Annuals, 5–50 cm. Leaves 5–40 × 3–17 mm. Involucres broadly turbinate, 5–10 mm. Phyllaries 24–44 in 3–5 series, lanceolate to linear-lanceolate, 4–9 × 0.7–1.5 mm, apices usually appressed, sometimes spreading, acute to acuminate. Receptacles convex, 2–3.5 mm diam. Ray florets 8–16; laminae 6–15 × 1–3 mm. Disc florets 14–40(–45); corollas 4–7 mm, glabrous or glabrate; lobes 0.7–1 mm, hairy (hairs multicellular), 0.2–0.5 mm. Cypselae 2–3.5(–4) mm; pappi 2–8 mm. 2n = 8.

Flowering Jul–Oct(–Dec). Grasslands, Larrea-dominated desert scrub, pine-oak woodlands, roadsides, streambeds; 700–1700(–2200) m; Ariz., N.Mex.; Mexico (Chihuahua, Sonora).

In the flora area, Machaeranthera tagetina occurs in southern and central Arizona and southwestern New Mexico, in the Chihuahuan and Sonoran desert regions. Much of its range in those states overlaps with that of M. tanacetifolia. In southern and central Arizona, the two species occasionally hybridize.