Taxonomy

Tridax procumbens L., Sp. Pl. 2: 900. 1753.

Common synonyms

Chrysanthemum procumbens (L.) Sessé & Moc. Fl. Mexic., ed. 2 190. 1894.

Common name

Coat buttons

Description

Propagule or dispersal unit is the fruit with pappus. Fertile part 2-2.5 mm long, 0.6-1 mm wide, in side view widest in upper part (obovoid), +/- straight, the upper (apical) end suddenly cut off (truncate), in cross-section round (terete), basal scar (carpopodium) pronounced and well-differentiated, central, beak (=thinner sterile stalk between seed and pappus) absent, wings absent, fruit surface dark brown or black, smooth (except at cellular level), with simple straight hairs, thickened margin absent, longitudinal ribs absent.

Pappus type bristles / hairs, pappus elements all +/- similar, up to 5-6 mm long, in one or several row(s), pappus elements numerous, persistent, the individual bristles feathery (plumose) along most of length, clearly wider at base, white / translucent or brown.

Notes: The surface of the fruit is marked with longitudinal lines under the hairs, but they have not been scored as ribs for this key because they do not visibly rise above the surface. Ripe fruits are black, but younger ones may still be brownish.

Ecology

Perennial herb, fruits wind-dispersed. Tropical, especially on coarse soils, does not tolerate waterlogging. Weed of roadsides, wasteland, fallow and agricultural land.

Native range

Central America.

Introduced range

Tropics worldwide: United States (especially Florida), Mexico, Caribbean, Colombia, Venezuela, Ecuador, Brazil, Argentina, southern Europe (?), tropical Africa, subtropical to tropical/southern Asia, Korea, Japan, Australia, New Zealand, Pacific Islands.

Past interceptions (Australia): origins

Mexico, Latvia, India, China, Thailand, Timor Leste, Papua New Guinea, Christmas Island, New Caledonia.

Other or unidentified species of the genus also from Korea, Vietnam.

Past interceptions (Australia): commodities

Containers, coir, agricultural machinery, machinery and parts, new vehicles, steel.

Other or unidentified species of the genus also in/on dried spices, bulk chemical fertiliser.