There are just 34 US species of the adoxaceae (muskroot, or elderberry) family, in three genera: adoxa, sambucus and viburnum, of which the latter is by far the most numerous, and is concentrated in the eastern half of the country. Plants are mostly shrubs or trees; they have toothed, opposite leaves, and dense, flat-topped clusters of small, five-petaled, radially symmetric flowers. Leaves may be simple or compound. Fruits are berry-like.