Within eastern North America, there appears to be some intergradation between the largely northeastern americana and the largely southwestern mexicana (Boonprakob et al. 2001; Shaw & Small 2004, 2005). Both taxa have acute-acuminate, glandless leaf-teeth; sepals usually lacking prominent marginal glands; relatively large petals (6-14 mm long); fruit relatively sour, becoming red or purplish, and usually with a glaucous bloom; 2n = 16. In Ky., flowering of typical americana occurs mostly during mid- to late Apr (about the same time as Cercis canadensis); this is true also for more hairy plants known as var. lanata, which have often been named P. mexicana. However, since "var. lanata" tends to occur on drier, warmer sites there may be some locally earlier flowering. Although plums in general are still widespread across Ky., extensive thickets have declined much since B's time and before. Historical records and associated place names (e.g. "Plum" along Cane Ridge in BOUR) suggest that several disturbed areas on fertile soils were formerly dominated by plums in the Ohio Valley. Strips occurred along major trails through some valleys and on some watershed divides of the Bluegrass region, often with Arundinaria gigantea (e.g. Beckner 1928, Campbell 1989; and continuing research). Remnants of plum thickets have largely disappeared from eastern states, but they still exist in varied forms further west (NS; type CEGL 1108). See also notes under angustifolia and munsoniana.