Taxonomy

Ageratum houstonianum Mill., Gard. Dict. ed. 8: Ageratum no. 2. 1768.

Common synonyms

Ageratum conyzoides subsp. houstonianum (Mill.) M.Sharma; Ageratum conyzoides subsp. houstonianum (Mill.) Sahu; Ageratum conyzoides var. houstonianum (Mill.) T.R.Sahu; Ageratum conyzoides var. mexicanum (Sims) DC.; Ageratum houstonianum f. houstonianum; Ageratum houstonianum f. luteum B.L.Rob.; Ageratum houstonianum f. niveum B.L.Rob.; Ageratum houstonianum f. normale B.L.Rob.; Ageratum houstonianum var. angustatum B.L.Rob.; Ageratum houstonianum var. typicum B.L.Rob.; Ageratum mexicanum Sims; Ageratum mexicanum Sweet; Ageratum mexicanum f. caeruleum Voss; Ageratum mexicanum f. mexicanum; Ageratum mexicanum f. wendlandii Voss; Ageratum mexicanum var. majus Voss; Ageratum mexicanum var. mexicanum; Ageratum mexicanum var. nanum Voss; Ageratum mexicanum var. wendlandii Voss; Ageratum wendlandii Bailly; Ageratum wendlandii; Ageratum wendlandii Hort. ex Vilm.; Cacalia mentrasto Vell.; Carelia houstoniana (Mill.) Kuntze

Common name

Mexican ageratum, blue billygoat weed, flossflower, bluemink, blueweed, pussy foot

Description

Propagule or dispersal unit is the fruit. Fertile part 1.5-2 mm long, 0.3-0.6 mm wide, in side view widest in upper part (obovoid), +/- straight or conspicuously curved, the upper (apical) end narrowing or suddenly cut off (truncate), in cross-section angular (prismatic), basal scar (carpopodium) pronounced and well-differentiated, off to the side (oblique) or at least asymmetric, rarely central, beak (=thinner sterile stalk between seed and pappus) absent, wings absent, fruit surface black, smooth (except at cellular level), with simple straight hairs, thickened margin absent, longitudinal ribs present, 5, their surfaces smooth, with simple straight hairs, rarely no hairs (glabrous).

Pappus type bristles / hairs and/or scales, pappus elements clearly differentiated, up to 0.5-2.5 mm long, in one or several row(s), number of pappus elements c. five, rarely six to ten, persistent, the individual bristles rough / serrated (barbellate), clearly wider at base, white / translucent or brown, the individual scales triangular to acute or dissected.

Ecology

Short-lived herb, fruits wind-dispersed. Tropical to warm-temperate areas. Found in gardens, wastelands, pastures, crops, wetlands, and along roads and creeks.

Native range

Mexico, Central America, Caribbean

Introduced range

United States (rarely collected), Colombia, Ecuador, Bolivia, Western Europe, tropical and south-eastern Africa, parts of tropical Asia (e.g. China, Taiwan), Papua New Guinea, eastern Australia, New Zealand