tropical whiteweed
Ageratum conyzoides L.
Tropical whiteweed has spread well beyond its original range. Kew lists introductions across many tropical and subtropical regions. Its worldwide distribution now includes places far removed from the Mexican native range recognized by that checklist. Kew POWO: Ageratum conyzoides
Botanical name
Kew accepts Ageratum conyzoides L. as a species. Kew POWO: Ageratum conyzoides
Recognizing the plant
Ageratum conyzoides has upright, hairy stems and toothed leaves. The small flower heads contain blue to lavender corollas, sometimes white. Flora of North America describes plants twenty to one hundred and fifty centimetres tall, ranging from annuals and perennials to partly woody subshrubs. Tiny fruits bear a crown of small scales, sometimes ending in bristle-like tips. Flora of North America: Ageratum conyzoides
Bloom window
Introduced North American populations
For the introduced U.S. populations it covers, Flora of North America records flowering in July and August. Flora of North America: Ageratum conyzoides
Native range
Kew’s current treatment identifies Mexico as native and lists extensive introductions elsewhere. Flora of North America instead describes the species as apparently native to South America. These sources therefore differ on its original distribution; neither treats its widespread cultivated escapes as evidence of universal nativity. Its habitat account places these plants on disturbed sites, mostly near the coast, at elevations of zero to twenty metres. Kew POWO: Ageratum conyzoidesFlora of North America: Ageratum conyzoides
Botanical sources
Reviewed 2026-10-11. Seasonal development varies with location and growing conditions.