Noun horseweed has 2 senses
- horse balm, horseweed, stoneroot, stone-root, richweed, stone root, Collinsonia canadensis - erect perennial strong-scented with serrate pointed leaves and a loose panicle of yellowish flowers; the eastern United States
--1 is a kind of herb, herbaceous plant
--1 is a member of Collinsonia, genus Collinsonia
- horseweed, Canadian fleabane, fleabane, Conyza canadensis, Erigeron canadensis - common North American weed with linear leaves and small discoid heads of yellowish flowers; widely naturalized throughout temperate regions; sometimes placed in genus Erigeron
--2 is a kind of weed
--2 is a member of Conyza, genus Conyza
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