Robinia pseudo-acacia L. - Black Locust

Robinia pseudo-acacia plant

Family - Fabaceae

Stems - Woody, single. A tree to +15m tall. Bark tan to light grayish. Paired spines present on younger branches. New seasons growth angled, sparsely pubescent.

Robinia pseudo-acacia twigTwig in winter.

Robinia pseudo-acacia budBud and spines.

Leaves - Alternate, odd-pinnate, typically with 7-19 leaflets. Leaflets oval to elliptic, opposite, glabrous when mature, entire, to +2cm long, +1.5cm broad.

Robinia pseudo-acacia leaf

Inflorescence - Drooping Axillary racemes to +15cm long. Typically 20-30 flowers per raceme. Peduncle and pedicles pubescent.

Flowers - Corolla papilionaceous, 2cm long and tall. Standard to 1.8cm broad and long, with yellowish spot in center. Stamens diadelphous, tube to 1.4cm long. Anthers orange, -1mm long. Ovary green, flattened, 1.5cm long, 1.1mm broad. Style 6.5mm long, pubescent at apex, upcurving near apex. Calyx tubular, bilabiate, sparsely to moderately pubescent, green mottled with red. Upper lip 3-4mm long, notched at apex. Lower lip 3-lobed. Lobes 2.5mm long. Fruits compressed, +1cm wide, +/- 7cm long.

Robinia pseudo-acacia calyxCalyx.

Robinia pseudo-acacia flower

Robinia pseudo-acacia fruitFruit, slightly larger than life size.

Flowering - May - June.

Habitat - Slopes, pastures, open woods, streambanks, roadsides.

Origin - Native to U.S.

Other info. - This tree is very common and is easily noticed when flowering. The flowers have a pleasant fragrance but each cluster only last a few days. My dad, who is the master of all things green and growing, recognized it from his days in Europe, where the tree also grows.

Photograph taken in Columbia, MO., 2-21-04 and 5-11-04.


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