Ageratum
whiteweed
often decumbent (rooting at proximal nodes), sparsely to densely branched.
cauline; all or mostly opposite;
petiolate;
blades mostly 1-nerved, deltate to ovate, or elliptic to lanceolate, margins entire or toothed, faces glabrous or ± pilose, puberulent, or strigoso-hispid, sometimes gland-dotted.
campanulate, 3–6 mm.
conic, epaleate [paleate].
20–125;
corollas white or bluish to lavender, throats ± campanulate (lengths 2 times diams.);
styles: bases not enlarged, glabrous, branches ± linear to clavate (usually papillose and dilated distally).
persistent, 30–40 in 2–3 series, usually 2-nerved, lanceolate, ± equal (often indurate, margins scarious).
discoid, in dense to open, cymiform to corymbiform arrays.
prismatic, 4–5-ribbed, glabrous or sparsely strigoso-hispidulous;
pappi persistent, of 5–6 aristate scales, or coroniform, or 0.
= 10.
Ageratum
Species ca. 40 (4 in the flora).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Plants colonial; stems and leaves glabrous or glabrate | A. maritimum |
1. Plants not colonial; stems and leaves hairy | → 2 |
2. Stems puberulent to minutely strigoso-hispid; cypselae glabrous | A. corymbosum |
2. Stems sparsely to densely pilose (usually in combination with other forms of vestiture); cypselae sparsely strigoso-hispidulous. | → 3 |
3. Peduncles minutely puberulent and sparsely to densely pilose, eglandular; phyllaries oblong-lanceolate, abruptly tapering to subulate tips 0.5–1 mm, glabrous or sparsely pilose, margins often ciliate, abaxial faces eglandular | A. conyzoides |
3. Peduncles mixed pilose, stipitate-glandular, and viscid-puberulent; phyllaries narrowly lanceolate, gradually tapering to indurate-subulate tips 0.8–2 mm, margins not ciliate or inconspicuously ciliate, abaxial faces stipitate-glandular and sparsely to densely pilose | A. houstonianum |
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