Gleditsia aquatica aka Swamp Locust

Gleditsia aquatica is a deciduous tree in the pea family. Its common names include water locust and swamp locust. It grows wild in the central and eastern United States. Its native range also reaches northeast Mexico. It lives in rich river valleys that flood. Some sites stay under water for much of the year.

This slow-growing tree has an open crown with spreading branches. Plants For A Future gives a height of 39 feet [12 metres]. Virginia Tech lists trees reaching 50 feet [15.2 metres]. One garden tree in Hampshire reached 23 feet [7 metres]. Its crown spread 26 feet [8 metres] across. Young bark is smooth and grey-brown, sometimes with mottled patches. Small pores mark the bark, which splits as it ages. The grey to red-brown twigs bend in a zigzag pattern. They bear clear thorns, and their side buds sit recessed.

The leaves grow alternately along the stems. They are pinnate or bipinnate, with 14 to 20 leaflets. Each leaflet has an oval or narrow oval shape. The whole leaf measures six to eight inches long. Small, pale green to whitish flowers form short racemes. They open after the leaves, and insects pollinate them. Chicago Botanic Garden records bloom from May to June. Plants For A Future gives July to August. The flat brown pods have an almost round shape. Each pod holds one to three seeds. Plants For A Future records seed ripening from October to December.

Full sun suits this tree, though Chicago also lists partial shade. It prefers moist to wet soil and grows well in loam. It can also grow in sandy or clay soils. It accepts mildly acid, neutral, and mildly alkaline ground. Chicago lists USDA hardiness zones 6–9. Young trees need cold protection during their first few winters. Plants For A Future reports better growth in southern Britain. The tree also tolerates air pollution.

Its light crown makes it useful in woodland gardens. It also serves as a shade tree or bog-garden tree. Its broad root system can help hold wet banks together. The hard, strong wood lasts well in soil. People use it for fence posts. Plants For A Future lists no known food or medicinal uses. It reports no known hazards, but the branches bear thorns.