Trees, (1–)4–25 m; branches finely pubescent or glabrate, eglandular. Leaves 20–30 cm; stipules 5–10 mm; petiole 0.7–2.5 cm, strigose; petiolules 2–3 mm, glabrate; leaflets (7–)15–19, blades elliptic, 25–45(–65) × 10–20(–25) mm, sur­faces glabrate. Racemes (10–)15–25-flowered, pendent, 5–19 cm, rachis sericeous; bracts lanceolate, 8–10 × 1 mm, margins entire. Pedicels 7–12 mm. Flowers: calyx tube 5–6 mm, sericeous, lobes 1–2 mm; corolla usually whitish, rarely pinkish, 15–20 mm. Legumes light to dark brownish, 4–10 × 1–1.5 cm, placental margin narrowly winged, glabrous. Seeds 4–8(–16).

Phenology: Flowering spring–early summer.
Habitat: Temperate, decidu­ous forests and woodlands, disturbed areas.
Elevation: 0–2000 m.

Distribution

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B.C., N.B., N.S., Ont., Que., Ala., Ariz., Ark., Calif., Colo., Conn., Del., D.C., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo., introduced in South America (Argentina, Chile), Eurasia, Australia.

Discussion

Robinia pseudoacacia is native at least in the Appalachian and other mountainous regions of eastern North America; it is widely cultivated and escaped throughout North America and other temperate regions of the world. Black locust can be highly invasive and is considered a threat to native biodiversity in many areas (J. Heim 1990; B. M. Farris 2007; L. Derickx and P. M. Antunes 2013). Populations growing at latitudinal extremes (such as Canada) are sometimes more likely to be shorter (3 m or less).

The report of Robinia pseudoacacia from Prince Edward Island is based on a single old specimen, and the species is here excluded from that province.

The winged and glabrous fruits and flowers with white petals arranged on pendent racemes set Robinia pseudoacacia apart from other species of the genus.

Nothospecies based on putative hybrids involving Robinia pseudoacacia and R. neomexicana (R. × holdtii Beissner, R. × coloradensis Dode) are found in areas where the former has been planted; those involving R. pseudoacacia and R. viscosa (R. × ambigua Poiret) are found in western North Carolina.

Selected References

None.

Lower Taxa

None.