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..
Trees or shrubs, with acrid resinous or milky sap, alternate or rarely opposite leaves, and polygamo-dioecious or perfect, mainly regular flowers. Calyx 3-7-cleft. Petals of the same number, imbricated in the bud, or rarely none. Disk generally annular. Stamens as many or twice as many as the petals, rarely fewer, or more, inserted at the base of the disk; filaments separate; anthers -commonly versatile. Ovary in the staminate flowers 1-celled. Ovary in the pistillate flowers 1- or sometimes 4-5-celled; styles 1-3; ovules 1 in each cavity. Fruit generally a small drupe. Seed-coat bony or crustaceous; endosperm little or none; cotyledons fleshy.
About 60 genera and 500 species, most abundant in warm or tropical regions, a few extending into the temperate zones.
Styles terminal; leaves compound; fruit nearly symmetrical.
Flowers in dense terminal panicles, appearing after the leaves.
Flowers in clustered spikes, appearing before the leaves.
Fruit glabrous, or sparingly pubescent, its stone striate.
Styles lateral; leaves simple; fruit gibbous.