Ulmus thomasii, commonly known as rock elm, is a native tree species primarily found in southeastern Ontario, particularly in the Kingston to Ottawa region. Rock elm can also be spotted along some roadsides in the Golden Horseshoe area. It is suitable for sandy, loamy, and clay soils, and prefers well-drained soil. While attractive in form, rock elm faces challenges, particularly from Dutch Elm Disease, a significant threat that also affects other native elms. Promoting the planting and preservation of rock elm where appropriate can help ensure its presence continues in the landscape. An alternative tree to plant is Ulmus hybrids or Ulmus americana.