Ageratum conyzoides
Ageratum maritimum
tropical whiteweed
Cape sable whiteweed
erect, sparsely to densely villous.
decumbent to straggling or creeping (rooting at nodes), glabrous but for puberulous-pilose nodes.
blades ovate to elliptic-oblong, 2–8 × 1–5 cm, margins toothed, abaxial faces sparsely pilose and gland-dotted.
blades deltate-ovate to oblong, mostly 0.8–4 × 0.5–3 cm, (fleshy) margins toothed, faces glabrous or glabrate.
minutely puberulent and sparsely to densely pilose, eglandular.
glabrous or glabrate.
3–3.5 × 4–5 mm.
ca. 3 × 3–4 mm.
usually blue to lavender, sometimes white.
lavender or blue to white.
oblong-lanceolate (0.8–1.2 mm wide), glabrous or sparsely pilose (margins often ciliate), eglandular, tips abruptly tapering, subulate, 0.5–1 mm.
elliptic-lanceolate, glabrous or glabrate, tips abruptly tapered to nearly obtuse.
sparsely strigoso-hispidulous;
pappi usually of scales 0.5–1.5(–3) mm, sometimes with tapering setae, rarely 0.
glabrous;
pappi usually blunt coronas ca. 0.1 mm, rarely of separate scales.
= 20, 40.
Ageratum conyzoides
Ageratum maritimum
Ageratum conyzoides is apparently native to South America. North American plants were escapes and naturalized from cultivation.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Plants from Florida (Ageratum littorale, the type from Florida) are described here. Plants of the West Indies and Mexico (broadening the species concept to A. maritimum, the type from Cuba) have various elaborations of vestiture and a more conspicuous pappus–coronas with even to laciniate margins or rings of nearly separate scales mostly 0.2–1.5 mm. In addition to the distinctive relatively small, glabrous or glabrate leaves, plants of A. maritimum are characterized by heads in clusters, usually held well beyond the leaves.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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