This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
Shrubs or trees having simple alternate usually toothed exstipulate leaves and regular hermaphrodite flowers. Calyx free or adherent to the ovary. Corolla of 4 to 8 more or less united petals, often differing in number from the calyx-lobes. Stamens double the number of the corolla-lobes or frequently more. Fruit drupaceous, or dry and winged, included in the calyx-tube or inferior, 1- to 5-celled; cells usually 1-seeded; seeds albuminous. A small group of about six genera and upwards of a hundred species, best known in gardens by the Snowdrop trees. The majority of the species are from the tropics of America and Asia.