This large tree species, a tetraploid (2n = 32), is widespread across eastern and central North America; it also extends south to Guatemala (Cr). In Ky. it is one of the most widespread woody species, based on occurrence of seedlings, but it is only locally dominant as mature trees, usually in young old-field woods or along fencerows. In full sun, trees grow fast and often exceed 100 cm dbh by 50 years old. The largest known trees in Ky. are reported from HARD (KDF 2020; 163 cm dbh. 27 m tall, 21 m wide) and from FAYE (pers. obs. in 2017): on Ball Homes development near Squires Road (157 cm dbh, 28 m tall, 22 m wide); and on Bell place along Newtown Pike (ca. 180 cm dbh but only ca. 100 years old). Flowering in Ky. is concentrated during late Apr to mid May (peaking about a week before Robinia pseudoacacia but greatly overlapping). There is much variation in dates of fruit-maturation, from Jun to Aug, and in leaf-fall. Also, there appears to be significant variation across eastern North America in overall tree form, leaf shape, serration, pubescence and glaucousness (on lower surfaces). However, no varieties are generally recognized within east-central states, except for the more southern P. alabamensis C. Mohr. Fresh leaf, wood and seed tissue of serotina, like most other species in tbe genus, contains significant amounts of cyanogenic glycosides (or "mandelonitrile" as a product), which can produce levels of cyanide toxic to mammals, especially within wilted foliage (Swain & Poulton 1994). Although generally controversial, there has also been continued scientific interest in potential use of such glycosides for treating cancers or other maladies (e.g. Abboud et al. 2018). However, the exceptional outbreak of abortions in thoroughbred horses during 2001 appears to have been caused by intestinal damage from setae of eastern tent caterpillars, which are specialists on Rosaceae, especially P. serotina (Gwaltney-Brant 2012).