Tridax

Perennials [annuals], 10–40[–80+] cm. Stems procumbent to ascending. Leaves basal and/or cauline; opposite; petiolate [sessile]; blades deltate, lanceolate, lance-ovate, or ovate, often pinnately or palmately lobed, ultimate margins coarsely toothed to subentire, faces glabrate, hirsute, scabrellous, or strigillose. Heads radiate [discoid], borne singly [in ± cymiform arrays]. Involucres cylindric to hemispheric, 4–8 mm diam. Phyllaries persistent, 11–15+ in 2–3+ series (outer usually shorter, more herbaceous, the inner often scarious). Receptacles convex to conic, paleate (paleae ± persistent, lance-linear, scarious, weakly conduplicate, often apically toothed). Ray florets [0–]3–8[–13], pistillate, fertile; corollas pale yellow [white or purplish]. Disc florets [20–]40–80+, bisexual, fertile; corollas yellowish [whitish or purplish], tubes shorter than cylindric or funnelform throats, lobes 5, usually deltate [sometimes rays 0 and corollas of peripheral florets ± bilabiate]. Cypselae obconic to obpyramidal, 3-, 4-, or 5-angled, densely piloso-sericeous [glabrous, villous]; pappi [sometimes wanting in rays] persistent, of [10–]20[–40], plumose [ciliate], setiform scales. x = 10.

Distribution

Introduced; mostly tropical, mostly New World.

Discussion

Species ca. 26 (1 in the flora).

Selected References

Powell, A. M. 1965. Taxonomy of Tridax (Compositae). Brittonia 17: 47–96.

Lower Taxa

Tridax procumbens