: Robinia pseudoacacia L. f. inermis, Robinia pseudoacacia L. var. pyramidalis, Robinia pseudoacacia L. var. rectissima
: False acacia, Yellow locust
: The nitrogen fixing capacity of this species may alter soil chemistry and subsequent nutrient cycling of forest systems.
: Deciduous medium tree ranging in height from 12-25 m (40-82 ft) and 30-60 cm (12-24 in) in diameter; crown narrow, open, irregular with contorted branches.
: Alternate, pinnately compound with 7-21 leaflets per leaf, leaf 20-35 cm (8-14 in) long, ovate leaflets 2-5 cm (1-2 in) long and about half as wide, thin with smooth margins, hairless, dull bluish green above paler beneath, turning yellowish brown in fall.
: Twigs puberulent, becoming smooth, green to reddish brown, with zigzag shape and two spines at each node; bark is thick, tan to gray-brown, deeply furrowed; inner bark orange.
: White in color, 5 petals, pea-like, very fragrant, raceme of 10-25 on a thin dangling pedicel; blooms May through June.
Fruit and seeds
: Seed pod, form in the fall but persist over winter, smooth, dark-brown in color, flat, contains 4-8 seeds.
: Very shade intolerant; can grow in many soil types except those with a high water table; formerly widely planted in Michigan and now found colonizing old fields, prairies, disturbed forests and woodlands.
: By seed. Also sprouts easily from roots and forms natural clones.
: Native honey locust (Gleditsia triacanthos
) has smaller, southern native bristly locust (Robinia hispida
) is shrublike with brushlike hairs on stems and fruit; False indigo (Amorpha fruitcosa
) shrublike with smaller leaves.
Monitoring and rapid response
: Monitor prairies and woodland edges and paths, particularly on well-drained soils; most visible in May and June while in flower but bark is distinctive year-round. Because this species is strongly clonal, all stems in a clone must be treated. Cutting and girdling stimulate sprouting unless cut stumps are treated with herbicide. Basal bark treatment is also effective. Fire stimulates resprouting; mowing stimulates germination of the (black locust) seed bank. This species is difficult to control, research control options thoroughly.
: The Michigan Natural Features Inventory
(MNFI) has partnered with MISIN to provide the information in this fact sheet. Species images and/or information were used with permission from "A Field Identification Guide to Invasive Plants in Michigan's Natural Communities
" and "A Field Guide to Invasive Plants of Aquatic and Wetland Habitats for Michigan