Ulmus thomasii Sarg. Rock Elm or Cork Elm Native to north-eastern N. America, sometimes planted there for shade and ornament and occasionally in botanical collections in Europe. Its wood is hard and strong, once much used in N. America. Height to about 30m (100ft). Flowers open in March in long slender clusters, each flower stem about 1.2cm (½in) long. Fruits (far right) are about 1.2cm (½in) long and downy, ripening in May. Leaves are rough at first with downy undersides, becoming smooth, dark green and shiny above, paler and downy underneath. Twigs often have corky wings, though not shown in photographs. Bark is dark brownish grey, with broad flaked ridges and fissures. Zone 2