| Noun | 1. | genus Ambrosia - comprising the ragweeds; in some classification considered the type genus of a separate family Ambrosiaceae asterid dicot genus - genus of more or less advanced dicotyledonous herbs and some trees and shrubs aster family, Asteraceae, Compositae, family Asteraceae, family Compositae - plants with heads composed of many florets: aster; daisy; dandelion; goldenrod; marigold; lettuces; ragweed; sunflower; thistle; zinnia ambrosia, bitterweed, ragweed - any of numerous chiefly North American weedy plants constituting the genus Ambrosia that produce highly allergenic pollen responsible for much hay fever and asthma |