Wood Anatomy of Elm (Ulmus) and Hackberry (Celtis) Species Native to the United States

Wood anatomy of Ulmus and Celtis species (Ulmaceae) native to the United States is described. Ulmus differs from ring-porous species of Celtis in ray structure, crystallocation, and colour and fluorescence of water extracts. The soft elms/non-winged bark species (Ulmus americana and Ulmus rubra) differ from the hard elms/winged bark species (U. alata, U. crassifolia, U. serotina, and U. thomasii) in density, earlywood pore diameter, and appearance of crystal-containing axial parenchyma. Some species of hard elm can be distinguished from one another by a combination of characters: water extract colour and fluorescence, earlywood pore diameter and spacing. The anatomy of ring-porous species of Celtis is unifonn, except that in C. reticulata earlywood pores have a smaller radial diameter than the other species. Celtis pallida is diffuse-porous and resembles other diffuse-porous species of the genus. Vessel element lengths are similar for all species within these two genera regardless of habitat.