Slippery Elm is a medium-sized tree, favouring alkaline substrate. It has a distinctive upright/spreading growth form and large thick-textured leaves with multiple forked veins, often with a pronounced fold along mid-vein. Buds are large, usually with reddish hairs. The bark can be scaly (somewhat similar to White Oak) or in long vertical grille-like ridges, greyer than Ulmus americana and its ridges not intersecting.
Slippery Elm is tolerant of dry uplands and found in understory or scattered in canopy of rich mesic forests (buds often nearly lacking reddish hairs in shade). Similar-looking to uncommonly cultivated Wych Elm (Ulmus glabra), which lacks reddish-hairs on buds. Quite visually distinctive compared to very common American Elm (Ulmus americana), which is nevertheless frequently confused with Slippery Elm, especially vigorous saplings which can have rough-hairy leaves. Slippery Elm’s leading branches often grow for some length at a consistently ascending 45 degree angle vs. the vase-like shape of American Elm.
Slippery Elm is uncommon in eastern Ontario, but can be locally abundant such as at Reveler Conservation Area and Fitzroy Provincial Park. At Fitzroy look for a grove of mature trees at the bottom of the waterfall at the start of the Terrace Trail. Scattered mature trees and populations occur throughout our region (see iNaturalist uploads) such as in the Carp Hills. There is an impressive, mature publicly-accessible tree at Mooney’s Bay (adjacent to Terry Fox Athletic Facility parking lot). Slippery Elm is commercially important for medicinal bark that soothes the colon. It freely hybridizes with dissimilar-looking invasive Siberian Elm (Ulmus pumila).
Here are selected photographs with location coordinates in iNaturalist: