This is a widespread southeastern species, extending north in somewhat disjunct populations to the greater Chicago area, low hills of w, W.Va. and pine barrens region of N.J. (K). It is closely related to the more northern munsoniana, hortulana and nigra (Shaw & Small 2005). These taxa are all diploids (2n = 16) that tend to share the following differences from the americana group: twigs generally more reddish-orange-brownish (versus purplish-grayish-blackish), more excurrent when vigorous (with longer leaders relative to branches) and with longer sharper thorns; leaves with relatively blunt, gland-tipped teeth, the upper surfaces generally more glossy, less rugose and more folded up along the midrib; flowers generally smaller (petals 3-9 mm versus 6-15 mm) and more continuous along long shoots (versus in distinct globular clusters often at base of short shoots); fruits usually becoming sweeter, red or yellowish (versus often purplish), without glaucous bloom. Flowering occurs mostly during late Mar to mid Apr, averaging 1-2 weeks earlier than the americana group but overlapping; also, flowers remain pure white (versus often fading pinkish). The angustifolia group requires full sun for fruit production; they do not survive long in woods or even partial shade, and were often cultivated around camps and villages of native people. Mature flowering plants in Ky. tend to be shorter and more thicket-forming, especially typical angustifolia (mostly 1-3 m tall versus 2-5 m in typical americana). Extensive thickets of angustifolia or its allies have virtually disappeared in Ky. and Tenn., but they persist locally in the Black Belt of Ala. and Miss. (NS: type CEGL 7747). Some outlying northern colls. of angustifolia may be from post-settlement plantings, as in FAYE (KY) at the old cabin above Elk Lick Falls; but in other cases plants probably originated earlier, as in POWE (JC) on the hills of Plum Branch. Plants at the old Annis Ferry in BUTL have at least three color forms in the fruit (yellowish, salmon-pinkish and deep red), also tasting different. These clones are adjacent to an ancient village site of the Mississippian era and before. P. angustifolia is presumably the plum referred to in De Soto's chronicles during his military tour of the southeastern states during the 16th Century: "finer than any grown in Spain" with "large quantities" of the dried fruits found stored in villages; see citations by C.W. Cowan in Ford (1985). Rafinesque (1836, 1:31-32) and other early botanists suggested that this species was spread to the north by Indian tribes. Moreover, it appears to have contributed about 18% to the gene pool of cultivated plums in southeastern states that largely originate in Eurasia (Boonprakob et al. 2001).