Tridax procumbens

Name and classification

Tridax procumbens L.
Family Asteraceae, Tribe Heliantheae

Common names

coatbuttons, tridax daisy

Disseminule

fruit

Description

Fruit an achene, narrowly obconic to cylindrical, tapering to a blunt base, 1.5–2.5 mm long, 0.5–1.4 mm in diameter (not including pappus). Blackish-brown, pilose, with pale ascending hairs, giving achene grayish-brown appearance. Pappus persistent, one row of ca. 20 straw-colored scalelike bristles, copiously long-plumose. Ray achene pappus 0.5–2.5 mm long, disc achene pappus alternately long and short, 3.5–6 mm long. Scar basal, a raised +/– elliptic pad, semi-transparent, striate. Apex horizontal, round, blackish, rough, with central style base; style base reddish-brown, cylindrical and hollow, or inconspicuous. Embryo straight, spatulate; endosperm absent.

Identification considerations

Tridax procumbens achenes are distinctive owing to their size, shape, and long-pilose covering. The persistent plumose pappus is diagnostic for the species. Compare to:

Haplopappus tenuisectus (Greene) Blake (non-FNW)

Haplopappus venetus (H.B.K.) Blake ssp. furfuraceus (Greene) Hall (non-FNW)

Distribution

tropics and subtropics throughout the world

native to Central America and tropical South America

Habitat

coarse-textured soils of tropical regions, open, sunny, dry localities; a weed of fallow land, fields, waste areas, roadsides

General information

Tridax procumbens is a semi-prostrate annual or short-lived perennial, with stems up to 50 cm long. It is a weed of pastures and a wide range of annual and perennial crop types. The persistent pappus enables the achenes to be carried by wind over a wide range. The large number of achenes produced per plant (50–-1500), as well as the plant's spreading stems, account for this species’ weediness and widespread distribution.

achenes

achenes

achene, detail

achene, detail

apex of achene

apex of achene

basal scar of achene

basal scar of achene

A, achene; B, achene with entire pappus; C, longitudinal section of achene showing embryo; D, transection of achene; drawing by Lynda E. Chandler

A, achene; B, achene with entire pappus; C, longitudinal section of achene showing embryo; D, transection of achene; drawing by Lynda E. Chandler