Gleditsia aquatica Marshall

Water Locust

© SRTurner

Family - Fabaceae/Caesalpinioideae

Habit - Tree, usually incompletely dioecious, often emergent aquatic.

Stems - Trunks 10-20 m tall, the bark smooth, becoming finely grooved and occasionally somewhat scaly with age, dull gray to reddish brown, usually armed with conspicuous thorns, these 6-15 cm long, 2-6 mm in diameter at the base, often clustered, simple or few-branched. Branches differentiated into short shoots with clustered leaves and elongate shoots with alternate leaves, the twigs of long shoots often somewhat zigzag, the winter buds partially sunken and inconspicuous.

	Trunk.
© SRTurner

	Stem.
© SRTurner

	Thorns.
© SRTurner

Leaves - Alternate, 1-2 times pinnately compound, appearing before flowers. Petiole 1-3 cm long. Petiole and rachis glabrous or nearly so. 1x compound leaves 12-15 cm long, with 7-10 pairs of leaflets, these 2-5 cm long, 0.5-1.5 cm wide, narrowly ovate, rounded to bluntly pointed at the tip, the surfaces glabrous, somewhat shiny. 2x compound leaves with 4-7 pairs of pinnae each with 7-9 pairs of leaflets, these 1.0-2.5 cm long, 0.5-1.2 cm wide, narrowly ovate to ovate, rounded to bluntly pointed at the tip, the surfaces glabrous, green to yellowish green, the upper surface shiny.

	Leaf.
© SRTurner

	Leaflets abaxial.
© SRTurner

Inflorescences - spikelike racemes 5-15 cm long with many flowers, the pistillate inflorescence with fewer and more widely spaced flowers than the relatively dense staminate ones. Flower stalks 1-3 mm long. Sepals 2.5-3.0 mm long, 0.8-1.5 mm wide, finely hairy. Petals 2.5-3.0 mm long, 1.5-2.0 mm wide.

Fruits - Legumes, relatively short, strongly flattened, the stalklike base 1-2 cm long, the body 3-5 cm long, asymmetrically elliptic or ovate, often twisted, glabrous, orange to reddish brown, lacking pulp. Seeds nearly circular, 10-12 mm long, 7-10 mm wide, brown.

	Fruits.
© SRTurner

Flowering - May - June.

Habitat - Swamps, sloughs, bottomland forests.

Origin - Native to the U.S.

Lookalikes - Gleditsia triacanthos, Robinia pseudoacacia.

Other info. - This swamp tree is found in Missouri's Bootheel, also ranging up the Mississippi River as far north as St. Louis. The continental U.S. range largely comprises a tight band moving southward through Louisiana, with more scattered populations along adjacent portions of the Gulf and Atlantic coasts.

Though the tree is most at home in swampy areas, it will grow under drier conditions and has sometimes been planted in yards and parks. As is the case with honey locust, thornless forms are sometimes found. The wood is durable and rot resistant and makes good fence posts. Hybrids with Gleditsia triacanthos have been reported from other states. These are intermediate in morphology and always found in proximity to the parents.

The species is most readily identified by its unique fruits. It can also be differentiated from G. triacanthos by its glabrous leaf petioles and rachises.

Photographs taken at Otter Slough Conservation Area, Stoddard County, MO, 10-18-2017, and at Mingo NWR, Stoddard County, MO, 9-10-2019 (SRTurner).