Six species of elm grow in the eastern United States: American (Ulmus americana), slippery (U. rubra), rock (U. thomasii), winged (U. alata), cedar (U. crassifolia), and September (U. serotina) elm. American elm is also known as white, water, and gray elm; slippery elm as red elm; rock elm as cork and hickory elm; winged elm as wahoo; cedar elm as red and basket elm; and September elm as red elm. American elm is threatened by two diseases, Dutch Elm disease and phloem necrosis, which have killed hundreds of thousands of trees.
Sapwood of elm is nearly white and heartwood light brown, often tinged with red. Elm may be divided into two general classes, soft and hard, based on the weight and strength of the wood. Soft elm includes American and slippery elm. It is moderately heavy, has high shock resistance, and is moderately hard and stiff. Hard elm includes rock, winged, cedar, and September elm. These species are somewhat heavier than soft elm. Elm has excellent bending qualities.
Historically, elm lumber was used for boxes, baskets, crates, and slack cooperage; furniture; agricultural supplies and implements; caskets and burial boxes; and wood components in vehicles. Today, elm lumber and veneer are used mostly for furniture and decorative panels. Hard elm is preferred for uses that require strength.
*Much of the base wood information presented here is made available by the USDA FPL FS. If you are interested in a much more technical description of wood properties, I encourage you to visit the source.