Black Locust (also known as False Acacia or Yellow Locust)

Species

Robinia pseudoacacia

Leaf Type

Pinnately compound, deciduous with pairs of opposite leaflets ending in a single terminal leaflet.

Family

Fabaceae (Legume or Pea family)

Shape

Leaflets are oval to elliptic or oblong-obovate with small rounded or notched tips (mucronate apex).

Size

Total compound leaf is approximately 6-12 inches (15-30 cm) long; individual leaflets measure about 1-2 inches (2.5-5 cm) long and 0.5-1 inch wide.

Margin

Entire (completely smooth edge without teeth or lobes).

Arrangement

Alternate along the stem; leaflets are arranged opposite to sub-opposite along the central rachis.

Rarity

Very Common; frequently aggressive or invasive outside its native localized range.

Color & Pattern

Medium to bluish-green on the upper surface, paler grayish-green beneath. No variegated pattern, but young growth is brighter yellow-green.

Venation Pattern

Pinnate venation on leaflets with a slender main midrib and fine secondary veins.

Texture & Surface

Smooth, thin, and slightly papery (glabrous to sparsely hairy when young), with a matte surface finish.

Description

A medium-sized deciduous leguminous tree capable of rapid growth and root suckering. It features compound leaves with smooth oval leaflets, paired stipular spines at leaf bases on young stems, fragrant white pea-like flower clusters in spring, and flat brown seed pods in autumn.

Key Features

Pinnately compound leaves with 7-19 smooth oval leaflets, paired sharp spines (modified stipules) at the nodes of young shoots, and fragrant drooping white flower racemes.

Habitat

Disturbed areas, forest edges, roadsides, pastures, and open woodlands. Thrives in dry to moist, well-drained, nutrient-poor sandy or gravelly soils in full sun.

Geographic Range

Native to the Appalachian Mountains and Ozark Plateau in the eastern US; widely naturalized across North America, Europe, Asia, and Southern Africa.

Condition Notes

Fair to Good. Minor leaf-miner damage (blistering/chlorosis) and small insect chewing holes visible on several leaflets, which is very typical for summer foliage on black locust saplings.

Interesting Facts

Black locust wood is extremely dense, rot-resistant, and strong, historically used for ship trunnels, railroad ties, and fence posts. The roots fix atmospheric nitrogen, helping it colonize poor soils.

Medicinal & Uses

Wood is widely used for outdoor posts, firewood, and rot-resistant timber. Blossoms are used to produce high-quality honey. Highly valued for land reclamation and erosion control.

Ecological Role

Provides nectar for honeybees and host plant for butterflies (like the Silver-spotted Skipper). However, it can become an aggressive invasive species forming dense monocultures that shade out native prairie or savanna flora.

Similar Species

Honey Locust (Gleditsia triacanthos, has smaller/doubly compound leaves and large branched thorns), Rose Acacia (Robinia hispida), and Siberian Peashrub (Caragana arborescens).

Foraging Tips

Look for paired thorns at the base of compound leaves and nitrogen-fixing root nodules. Only the white flowers are safely edible after cooking; all other plant parts are toxic.

Toxicity Warning

Highly Toxic. Leaves, bark, roots, and seeds contain toxic lectins (robin) and proteins. Ingestion causes severe gastrointestinal distress, weakness, and central nervous system depression in humans and livestock (especially horses).

Identified on 7/26/2026