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..
Annual or perennial herbs, the stems erect or twining. Leaves opposite or sometimes alternate, toothed, lobed, or divided, petioled, the stipules persistent. Flowers dioecious; staminate flowers in panicled racemes, usually 5-parted; pistillate flowers in bracted spikes, the perianth entire, the ovary 1-celled, the styles or stigmas 2, the ovule pendulous. Fruit an achene, with crustaceous pericarp. Endosperm fleshy; embryo curved or coiled.
Twining vines; pistillate flowers in ament-like clusters.
Erect, tall herbs; pistillate flowers spicate.