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Heracleum (family Umbelliferae) A genus of coarse, biennial or perennial herbs. H. mantegazzianum (giant hogweed) grows to 3 m tall with umbels 1 m in diameter and produces a highly irritant sap; it is native to the Caucasus but naturalized in Europe, and is a noxious, invasive weed. There are about 60 species, occurring in northern temperate regions and tropical mountains.