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Ageratum L.


Ageratum conyzoides

Credit: HAST

Erect herbs. Leaves opposite or upper ones alternate, petiolate, ovate, dentate or serrate, penninerved. Heads in corymbs or loose panicles, homogamous, discoid, many-flowered. Involucre campanulate, bracts imbricate, 2-3 seriate, linear, acute to acuminate, subequal; receptacle flat or nearly so, naked or with caducous scales. Corollas all tubular, equal, regular, limb 5-fid. Anthers with an apical appendage, base entire, obtuse. Style arms long, slender, obtuse, pubescent at apex. Achenes oblong, 5-angular. Pappus uniseriate, of 5 short free or connate scales, or of 10-20 narrow acuminate unequal scales.

About 40 species in tropical America and the West Indies; two widely adventive species naturalized in Taiwan.


1 Lower surface of leaves glandular punctate (at 10×magnification); involucral bracts sparingly hairy or glabrous, serrate apically; pappus scales slightly longer than or equal to corolla; corolla white or somewhat bluish.   Ageratum conyzoides
+ Leaves not glandular punctate beneath (at 10×magnification); involucral bracts manifestly hairy, entire; pappus scales shorter than corolla; corolla violet.   Ageratum houstonianum

Lower Taxa


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