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 alternate pinnately veined or pinnate petioled leaves, the small deciduous stipules free from the petiole. Flowers regular, perfect, racemed, cymose or solitary. Calyx mostly 5-toothed or 5-lobed, its tube (hypanthium) adnate to the ovary. Petals mostly 5, usually clawed. Stamens numerous or rarely few, distinct; anthers small, 2-celled, the sacs longitudinally dehiscent.
Ovary 1-5-celled, usually 5-celled, composed of 1-5 wholly or partly united carpels, borne within the hypanthium and adnate to it; ovules 1-2 (rarely several) in each carpel, anatropous, ascending; styles 1-5; stigma small. Fruit a more or less fleshy pome, consisting of the thickened calyx-tube enclosing the bony papery or leathery carpels. Endosperm none; cotyledons fleshy.
About 20 genera and probably not fewer than 500 species, of wide geographic distribution. Ripe carpels papery or leathery.
Leaves simple, entire, toothed, or lobed.
Cavities of the ovary (carpels) as many as the styles.
Flesh of the pome with grit-cells.
Flesh of the pome without grit-cells.
Cymes simple; trees.
Cymes compound; low shrubs.
Cavities of the ovary becoming twice as many as the styles.
Ripe carpels bony.
Ovule 1 in each carpel, or if 2, dissimila*.
Ovules 2 in each carpel, alike.