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..
Prunus americana Marsh. Arb. Am. 111. 1785.
A shrub or small tree, maximum height about 350, and trunk diameter about 12'; branches more or less thorny; bark thick. Leaves ovate or obovate, acuminate, nearly or quite glabrous when mature, usually pubescent when young, sharply and often doubly serrate, with gland-tipped teeth, rounded at the base, slender-petioled; petioles usually glandless; flowers white, 8"-12" broad, appearing in lateral sessile umbels before the leaves; pedicels 5"-9" long; calyx-lobes pubescent within, entire; dnipe globose, red or yellow, 9"-12" in greatest diameter, the skin tough, bloom little or none, the stone somewhat flattened, its ventral edge acute or margined, the dorsal faintly grooved.
Connecticut to Montana, Florida, Texas and Colorado. A southwestern race has very pubescent leaves. April-May. Fruit ripe Aug.-Oct. Horse-, hog's- or goose-plum. Native plum. Plum-granite.
A tree, 20°-30° high, the trunk sometimes 10' in diameter, the bark thin. Leaves oval, ovate or obovate, long-acuminate, pubescent when young, crenulate-serrate, narrowed, obtuse or subcordate at the base, 3-5' long; petioles stout, 1/2'-1' long, bearing 1 or 2 red glands near the blade; flowers in lateral umbels, expanding before the leaves, 1'-1 1/4' broad; pedicels 6"-10" long, slender, glabrous; calyx-lobes glandular-serrate, glabrous within, sometimes pubescent without; petals white, turning pink; drupe oval, 1'-1 1/3' long, yellow to orange-red, thick-skinned, bloom little or none, the flesh adherent to the oval compressed stone, which is sharply ridged on the ventral edge, somewhat grooved on the dorsal.
P. hortulana Bailey, Gard. & For. 5: 90. 1892. Prunus hortulana Mineri Bailey, Bull. Cornell Agric. Exp. Sta. 38: 23. 1892.
A small tree, similar to the two preceding; branches spreading, bark thin. Leaves ovate-lanceolate to ovate or oblanceolate, long-acuminate, somewhat peach-like, closely glandular-serrate, glabrous, 4'-6' long; petioles not 1' long, usually bearing two glands near the blade; flowers few in the lateral umbels, expanding before the leaves; pedicels 5"-10" long; calyx-lobes glandular-serrate, pubescent without and within; drupe subglobose or short-oval, bright red, thin-skinned; stone swollen, not margined; bloom little or none.