This taxon may be reasonably treated as a variant of U. minor Mill., which is a widespread complex species in southern Europe (FNA 3). U. procera is often called "English elm" but it is a generally sterile clone that originates from southeast Europe; root-suckers are often persistent and spreading (Gil et al. 2004). It has been planted across much of North America, with local escapes reported mostly from northeastern regions (K). In Ky. J noted that this tree can occasionally escape, but there are no known supporting colls. The large tree in front of the old Agriculture Experiment Station on the Univ. of Ky. campus (now dead) was mislabeled as rubra for 30 years (despite the error being pointed out more than once). The National Champion tree for rubra was reported in 2014 from the Masonic Homes of JEFF (KDF 2020; see also americanforests.org), but this tree is procera: 228 cm dbh, 27 m tall, 25 m broad (presumably dating from the early 1800s). Trees of the minor complex often reach 200-250 cm in dbh or 30-40 m in height (Clapham et al. 1962, Bean 1978). The European species in subgenus Ulmus (minor, procera, glabra) can be distinguished from rubra as follows (FNA 3, W): samaras glabrous except on margins or central vein (versus pubescent on body); leaf blades averaging smaller, mostly 5-15 cm long (versus 10-15 cm) and broader in shape, with L/W mostly 1.6-1.7 and often suborbicular in procera (versus 1.6-2), eciliate (versus ciliate), upper surfaces scabrous to glabrate (versus harshly scabrous with longer antrorse trichomes); bud scales brown with ciliate margins (versus red with tomentose margins). U. procera differs from U. glabra Huds. as follows (Clapham et al. 1962; FNA 3, W): leaf base oblique but not overlapping the petiole (versus strongly oblique, the lower side overlapping the petiole. which is only 1-3 mm), blades averaging smaller, mostly 5-10 x 4-6 cm (versus 7-15 x 4.5-8 cm), scabrid to glabrescent above (versus persistently scabrid); older branchlets often with corky wings (versus not so); samaras rarely produced (versus annually), glabrous except along the margin of the notched apex (versus glabrous except along central vein). All of these species are susceptible to Dutch Elm Disease, but rubra appears to be killed much less often than americana in Ky.