After 1970, a few selections of this Chinese tree became promoted for ornamental use across eastern states due to their rapid growth and profuse early blossoms,mostly during early Mar to early Apr, starting well before native rosaceous trees and shrubs. But a curious feature of this species is the putrid "fishy" smell from dense populations of flowering trees on warm spring days. Although often reported, this odor does not appear to have been studied or identified in chemical terms; see also notes under Photinia. The original "Bradford" and later "Aristocrat" became some of the most widely distributed, clonally propagated cultivars. Although often marketed as thornless, most or all plants have capacity for reversion to a dangerously thorny condition in stump sprouts and saplings from seed. This species did not appear to be invasive af first, but its spread accelerated during the 1990s apparently due to the increased variety of cultivars, leading to more fertile cross-pollinated seed (Vincent 2005; Culley & Hardiman 2007, 2009; Culley 2017, FNA9). Fruits are dispersed by a diversity of birds and mammals (including deer). In Ky. all naturalized records date from after 1993 (M), and calleryana is now becoming common to locally dominant in urban areas and along major highways. Vincent provided many new records in Ky., and R. Thompson in more recent years (BEREA). The taxonomy of Pyrus is complicated by varied parentage in some cultivars that are often grouped with calleryana. Most pears are diploids (2n = 34) and can interbreed (Zheng et al. 2014). P. calleryana is closely related to the Himalayan P. pashia L. and the Southeast Asian P. pyrifolia (Burmann f.) Nakai. It is possible that some cultivars presumed to be calleryana have hybrid origin, and that there is segregated expression of a non-calleryana parent in the naturalization of these plants. See further notes under "cf. bretschneideri."