Tridax procumbens L.
Family Asteraceae, Tribe Heliantheae
coatbuttons, tridax daisy
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.
Haplopappus tenuisectus (Greene) Blake (non-FNW)
Haplopappus venetus (H.B.K.) Blake ssp. furfuraceus (Greene) Hall (non-FNW)
tropics and subtropics throughout the world
native to Central America and tropical South America
coarse-textured soils of tropical regions, open, sunny, dry localities; a weed of fallow land, fields, waste areas, roadsides
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.