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Tridax procumbens L.
Family: Asteraceae, Tribe: Heliantheae
Common names: 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 linear; endosperm absent.
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
Haplopappus venetus (H.B.K.) Blake ssp. furfuraceus (Greene) Hall
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 speciesí weediness and widespread distribution.