"Fraxinus pennsylvanica" is a medium-sized deciduous tree reaching (rarely to ) tall with a trunk up to in diameter. The bark is smooth and gray on young trees, becoming thick and fissured with age. The winter buds are reddish-brown, with a velvety texture. The leaves are long, pinnately compound with seven to nine (occasionally five or eleven) leaflets, these (rarely ) long and broad, with serrated margins and short but distinct, downy petiolules a few millimeters long. They are green both above and below. The autumn color is golden-yellow and depending on the climate, Green Ash's leaves may begin changing color the first week of September. The flowers are produced in spring at the same time as the new leaves, in compact panicles; they are inconspicuous with no petals, and are wind-pollinated. The fruit is a samara long comprising a single seed long with an elongated apical wing long and broad.