This widespread eastern tree generally occurs in mesic or submesic woods, avoiding drier or wetter sites. However, americana has become much more common on some farmed uplands (where often misidentified as rubra), while rubra remains concentrated in more wooded landscapes. The effects of livestock, including free-ranging pigs, have probably been significant. In FAYE, Short (1828-29) noted that the species "has almost disappeared from the forest around Lexington in consequence of its destruction by cattle... In the more inaccessible situations among the cliffs of Elkhorn and the Kentucky river, it is occasionally met with... The inner bark is medicinal, being mucilaginous and demulcent"; see also Watts (2012). The bark was sometimes an important food for starving humans on the frontier; for example, N. Boone (Hammon 1999, p. 57) recalled: "I have heard my father speak of the want of food and of eating slippery elm bark (rather loosening) and then oak bark ooze by chewing to counteract any bad effects." U. rubra has often been confused in vegetative specimens with americana or other species, but there are differences (F, Y, FNA 3, J, W). Leaves of rubra have relatively large size (mostly 10-15 cm long versus 7-12 cm), somewhat obovate with a more abruptly acuminate apex, marginally ciliate, with longer hairs on upper surfaces (up to ca. 1 mm versus 0.5 mm, like a 24 hour beard versus 12 hour), and tomentose to villous below (versus slightly pubescent to glabrous except for axilary tufts). A simple distinguishing trick with fresh leaves (learnt from D. Boone) is to slap an upper surface to the palm of one's hand; this species sticks but other elms do not, at least in Ky. Vegetative buds are obtuse (versus acute), the scales red with tomentose margins (versus reddish-brown with pubescent surface). The bark of mature trees is dark brown in cross-section (versus alternating light and dark). U. rubra, with reliable identification, is generally reported no more than 90-150 cm dbh and 20-25 m tall (Sm, Cr). The closely related European species, U. glabra Huds. (which extends into boreal regions) and U. procera Salisb. ("English Elm"), often grow to larger sizes and have occasionally been planted, then confused with rubra given inadequate keys in some North American treatments; see notes under procera. Compared to congeners in North America (FNA 3), all three species (sect. Ulmus) generally differ as follows: calyx pubescent (versus usually glabrous) flowers and fruits sessile or with pedicels only 0-2 mm long (versus 5-20 mm), in dense non-pendulous fascicles (versus pendulous in fascicles or racemes); samaras usually pubescent at least in part but not ciliate on margin (versus glabrous or pubescent on body and usually ciliate on margin); buds more or less obtuse (versus acute); upper leaf surfaces at least slightly scabrous, even on fertile branches (versus glabrous or scabrid); lower surfaces pubescent and with distinct tufts of hairs in the vein axils (versus pubescent or glabrous, with or without tufts).