This widely planted tree ("Siberian elm") was first recorded as an escape in Ky. by Ellis et al. (1971; APSC). However, it has not been generally recommended for ornamental uses during recent decades, due to brittle branches, pests and pathogens (missouri botanical garden.org).The colls. mapped here appear to be from self-seeded plants, based on label data. Most data come from CW, who indicated that this species is becoming naturalized across the state, especially in urban areas. However, well-documented invasion appears to be rare in most of Ky. and in more southeastern states. Further west, especially in the Great Plains, this species is much more commonly naturalized (K). It can hybridize extensively with rubra, and it is generally somewhat resistant to Dutch Elm Disease (Zalapa et al. 2010; Elowsky et al. 2013). An apparent hybrid has been found during 2025 at the south side of Panera n FAYE (JC at 38.00780, -84.45143). In Nebraska, Elowsky et al.(2013) found that hybrids (named X intermedia) differed from pumila as follows: leaves 4.5-12 × 2.5-6 cm (versus 4-7 x 1.5-3.5 cm), scabrous to glabrous (versus glabrous), , margin "primarily triply serrate" as in rubra (versus doubly or rarely singly), apex acuminate to acute (versus acute); floral buds relatively large,the scales fully pubescent or marginally with red and white trichomes (versus with only white marginal trichomes); leaves drying with a dull, lustrous silver cast (versus to dull green).