236. Ageratina Spach, Hist. Nat. Vég. 10: 286. 1841.
紫茎泽兰属 zi jing ze lan shu
Shrubs or perennial herbs, usually erect. Leaves usually opposite; blade narrowly elliptic to deltate, mostly toothed, lobed, serrate, or crenate. Capitula laxly to densely corymbose. Phyllaries ca. 30, 2- or 3-seriate, distant to weakly subimbricate, mostly subequal; receptacle usually slightly convex, glabrous or with minute scattered hairs. Florets 10-60, often sweetly scented; corollas white or lavender, usually with slender basal tube and campanulate limb (in A. subg. Ageratina and A. subg. Klattiella), others narrowly funnelform; lobes distinctly longer than wide, outer surface smooth, glabrous or glandular, usually with hairs (in A. subg. Ageratina), inner surface densely papillose; antheropodium cylindric, usually elongate; anther appendage large, ovate-oblong, longer than wide; style base usually enlarged [except in A. subg. Apoda]; style branches rarely slightly broadened distally, densely papillose with projecting cells on lateral and outer surfaces. Achenes prismatic or fusiform, usually 5-ribbed, setuliferous or glandular or both; carpopodium distinct (cylindric in A. subg. Ageratina) [in others rounded or broadly stopper-shaped]; pappus setae uniseriate, 5-40, barbellate, often easily deciduous, capillary, often enlarged distally, often with outer series of shorter setulae. x = 17.
About 265 species: tropics and subtropics of the New World; one species (introduced) in China.
King and Robinson (Phytologia 19: 208-229. 1970) first provided an infrageneric division recognizing four subgenera, later raising Ageratina subg. Pachythamnus R. M. King & H. Robinson to generic status. Subsequently (King & Robinson, Phytologia 38: 323-355. 1978), they recognized two further subgenera. A complete list of species in the five subgenera was provided by King and Robinson (Monogr. Syst. Bot. 22: 1-581. 1987).
See B. L. Turner’s The Comps of Mexico, Vol. 1 (Phytologia Mem. 11: i-iv, 1-272. 1997).