This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Mostly vines, with woody or herbaceous, often prickly stems. Leaves alternate, netted-veined, usually punctate or lineolate, several-nerved, petioled. Petiole sheathing, bearing a pair of slender tendril-like appendages (stipules?), persistent, the blade falling away. Flowers small, mostly green, dioecious, in axillary umbels. Perianth-segments 6. Stamens mostly 6, distinct; filaments ligulate; anthers basi-fixed, 2-celled, introrse. Ovary 3-celled, the cavities opposite the inner perianth-segments; ovules 1 or 2 in each cavity, orthotropous, suspended; style very short or none; stigmas 1-3. Fruit a globose berry containing 1-6 seeds. Seeds brownish; endosperm horny, copious; embryo small, oblong, remote from the hilum.
Genera 3; species about 200, in warm and temperate regions; only the following in North America.