The perfect apetalous, wind-pollinated flowers are red-green and appear in racemes up to 40 mm (2 in) long two weeks before the leaves from March to May, depending on the tree's location.

The fruit is a broad ovate samara 13–25 mm (1⁄2–31⁄32 in) long covered with fine hair, notched at the tip, and maturing during May or June to form drooping clusters at the leaf bases.

[11] Seedlings arising from crossings with Siberian elm (U. pumila) at the Lake States Forestry Experimental Station in the 1950s all perished,[19] a classic case of hybrid lethality.

It is also very strong and takes a high polish, and consequently was once in great demand in America and Europe for a wide range of uses, notably boatbuilding, furniture, agricultural tools, and musical instruments.

Much of the timber's strength is derived from the tight grain arising from the tree's very slow rate of growth, the trunk typically increasing in diameter by less than 2 mm (3⁄32 in) a year.

Over 250 annual growth rings were once counted in a log 24 cm (9+1⁄2 in) square being sawn for gunwales in an English boatyard, while a tree once grown at Kew Gardens, London, attained a height of only 12 m (39 ft) in 50 years.