Acmella

Annuals or perennials, 10–20(–30+) cm. Stems prostrate to erect, usually branched ± throughout. Leaves cauline; opposite; petiolate [± sessile]; blades (usually 3-nerved) ovate to rhombic or lanceolate [linear to filiform], bases ± cuneate, margins entire or toothed, faces sparsely pilose to strigillose, glabrescent. Heads radiate or discoid [disciform], borne singly at tips of branches [corymbiform arrays]. Involucres ± hemispheric to ovoid, 3–6+ mm diam. Phyllaries persistent, 8–15+ in 1–3 series (distinct, ovate to linear, subequal or outer longer). Receptacles conic, paleate (paleae falling with fruit, ± navicular, membranous to scarious, each about equaling subtended floret). Ray florets 0 or 5–20+, pistillate, fertile; corollas yellow to orange [white or purplish] (laminae ovate to linear) [wanting]. Disc florets 25–100(–200+) bisexual, fertile; corollas yellow [orange], tubes shorter than campanulate throats, lobes 4–5, deltate. Cypselae 2–3-angled (peripheral) or strongly compressed, ellipsoid to obovoid (glabrous or ciliate on the 2–3 angles or ribs); pappi 0, or fragile, of 1–3 awnlike bristles. x = 13.

Distribution

s United States, Mexico, West Indies, Central America, South America, introduced in Asia, Africa, Pacific Islands, Australia.

Discussion

Species 30 (2 in the flora).

Acmella pilosa R. K. Jansen has been reported as introduced in Florida (http://www.plantatlas.usf.edu); it differs from A. repens mainly by its more densely pilose stems and leaves and more truncate to cordate (versus cuneate) leaf bases.

Selected References

Jansen, R. K. 1985. The systematics of Acmella (Asteraceae–Heliantheae). Syst. Bot. Monogr. 8: 1–115.

Lower Taxa

Acmella pusilla, Acmella repens

Key

1	Petioles 3–40+ mm; leaf blades ovate to lance-ovate, mostly 20–40(–100) × 10–35 mm, margins dentate to denticulate or entire	Acmella repens
1	Petioles 2–4 mm; leaf blades lanceolate, mostly 12–40 × 3–10 mm, margins usually sinuate-dentate, rarely entire	Acmella pusilla