20. Prunus L. (cherry, plum, peach, apricot)

Plants shrubs or small to medium trees, sometimes colonial from root suckers. Branches sometimes producing short, stout branchlets with thorny tips. Bark dark reddish brown to brown or dark gray, on younger trunks relatively smooth and sometimes somewhat shiny, but with prominent, raised branch scars and light-colored lenticels in transverse lines, on older trunks usually developing more or less rectangular, fine, scaly plates, these sometimes peeling. Winter buds lateral and terminal or pseudoterminal (then produced in groups of 2 or 3 at the twig tips), narrowly ovoid to narrowly conic, usually sharply pointed at the tip, with several overlapping scales. Leaves alternate but sometimes appearing clustered at the tips of short branchlets, rolled or folded lengthwise during development, usually short-petiolate, the petioles sometimes with 1 to several variously shaped glands near the tip. Stipules linear to lanceolate, membranous to papery, the margins toothed or lobed and frequently glandular, shed early. Leaf blades simple, unlobed, variously shaped, the margins entire or more commonly bluntly to sharply toothed, occasionally appearing finely scalloped, the teeth sometimes gland-tipped, the surfaces glabrous or hairy, the upper surface lacking glands, sometimes shiny, the venation with a midvein and pinnate secondary veins, these sometimes faint. Inflorescences terminal and/or axillary, on main branchlets or more commonly on lateral, short branchlets, variously solitary flowers, umbellate clusters, or racemes of few to many, short- to long-stalked flowers, produced before or as the leaves uncurl, the axis and stalks glabrous or hairy, the stalks each with a small bract at the base, this linear to narrowly oblong-elliptic, shed early. Flowers deeply perigynous, sometimes sweetly fragrant or with an unpleasant odor, the hypanthium not fused to the ovary above its base, cup-shaped to bell-shaped or more or less urn-shaped, shed after flowering or less commonly persistent as a small disc, glabrous or hairy. Sepals 5, ascending to reflexed at flowering, triangular to oblong-ovate or oblong, sharply pointed to rounded at the tip, the margins entire or toothed (the teeth often gland-tipped), the inner surface usually woolly, the outer surface glabrous or hairy, shed with the hypanthium after flowering (persistent in P. serotina). Petals 5 (except in doubled forms), elliptic to obovate or nearly circular, rounded or short-tapered to a short, stalklike base, white or less commonly pink. Stamens usually 10–20(–30) (usually fewer in doubled flowers), exserted, the anthers yellow or pink to red. Pistil 1 per flower, of 1 carpel. Ovary superior, with 1 locule containing 2 ovules (1 of these usually abortive). Style 1, the stigma capitate to more or less disc-shaped. Fruits drupes, globose to oblong-ovoid or broadly ellipsoid, in some species with a longitudinal groove along 1 side, glabrous or less commonly hairy at maturity, variously colored, the surface usually not dotted (white-dotted in P. hortulana), with 1 seed embedded in a hard stone (sometimes called a pit), this mostly thick-walled, indehiscent, globose to ovoid, sometimes somewhat flattened, the surface smooth or with a network of ridges, furrows, and pits. About 200 species, nearly worldwide, most diverse in temperate regions of the northern hemisphere.

The genus Prunus contains a number of important fruit crops, including peaches, nectarines, apricots, pluots, plums, and cherries. Secondarily, the fleshy-fruited species are used in baked goods, juices, jams and preserves, and as flavorants. The almond (P. dulcis (Mill.) D.A. Webb) is anomalous among the fruit crops in that its fruit has a leathery rather than fleshy middle layer of the fruit wall, which is removed, and the thin-walled stone is marketed as a nut. A large number of species, hybrids, and cultivars are important as flowering ornamentals and the larger species also are planted as shade trees. The wood of various species has a wide variety of uses, from firewood to pipe stems, and has been used in furniture, tool handles, rifle stocks, handcrafts, veneers, paneling, flooring, scientific and musical instruments, and caskets. Some of the species have been used in a variety of ways medicinally.

Some botanists have split Prunus into a number of smaller genera, including Amygdalus L., Armeniaca Scop., Cerasus Mill., Lauro-cerasus Duhamel, Padus Mill., and/or Persica Mill. These correspond more or less to groups recognized as subgenera and sections by other botanists. However, there is no agreement on how many units should be recognized (K. R. Robertson, 1974), and preliminary molecular studies (Bortiri et al., 2001, 2002; Lee and Wen, 2001) have cast doubt on whether most of these groups are natural. A taxonomic reappraisal of the genus must await more detailed studies. The present account follows closely the forthcoming treatment of the genus Prunus in the Flora of North America series by Joseph Rohrer.