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Contains about 100 genera and 3350 species of trees, shrubs, and herbs, distributed throughout cooler regions of both hemispheres. Includes many important ornamentals (Rhododendron, Kalmia, etc.); many with edible fruit (Vaccinium and Gaylussacia), some with leaves poisonous to livestock (Kalmia, etc.), and many which grow well in very acidic conditions (Rhododendron, Kalmia).