The rhamnaceae (buckthorn family) is a group of shrubs, vines and small trees, with around 100 US members, in 15 genera, concentrated in the south and southeast. Leaves (evergreen or deciduous) are unlobed, alternate or opposite, often toothed, and they usually have stipules at the base. Some or all leaves may be replaced by spines. Flowers are generally small, arranged in dense clusters; they most often have five petals, five sepals and five stamens, attached to a cup-shaped structure, the hypanthium, below which is a thin nectary tube. Some species have flower parts in fours rather than fives. Flowers are mostly colored white, pale blue or pale pink. Fruits are berries.