This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol2", 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..
Large trees, with thin exfoliating bark, alternate petioled palmately lobed and veined leaves, the hollowed petiole bases enclosing the buds for the following season, and very small green monoecious flowers in dense globular heads. Receptacle somewhat fleshy. Flowers very small, bracted; calyx and corolla apparently none. Staminate flowers with 3-8 stamens; filaments short; connective broad, dilated; anthers oblong or linear, longitudinally dehiscent. Pistillate flowers with 2-9 distinct pistils and several staminodes; ovary linear, 1-celled; style elongated; stigma lateral. Ripened head of fruit composed of very numerous narrowly obpyramidal nutlets which are densely pubescent below with long nearly erect hairs. Seed pendulous; endosperm thin; cotyledons linear.
The family contains only the following genus, comprising some 8 species, natives of the north temperate zone. Its relationship to other families is doubtful.