Locust, Idaho Flowering
Robinia x ambigua
Fabaceae - Legume

Description

Leaves: Presumably similar to the leaves of black locust: dark green in summer, yellow-green fall color, hairless; alternate; pinnately compound, 8" to 14" long; 7 to 19 elliptical and ovate-oblong or ovate leaflets, 1-1/2" to 2" long, entire margins; deciduous.

Twigs/buds: Similar to black locust: twigs moderately stout; often zigzag; generally have short, stiff spines, 1/4" to 1/2" long, in pairs at bases of leaves. No terminal bud; lateral buds hidden under cracks of bark near leaf scar.

Flowers/fruit: Flowers perfect; rose-pink; occur in late spring (May to June); fragrant; 1" long, but part of longer (6" to 8" in length), hanging racemes. Fruit similar to black locust; dark brown, flat legume; 3" to 5" long; containing 4-8 flat brown seeds.

Bark: Red-brown to nearly black; deeply furrowed into cris-crossing scaly ridges; inner bark may be poisonous.

Wood: Unimportant; presumably similar to that of black locust.

General: Probably a hybrid of black locust (R. pseudoacacia) and bristly locust (R. hispida) or R. viscosa. Often reaches heights of around 25' to 40' and a spread of 15' to 30', with a medium growth rate. Tough and tolerant of difficult conditions, including heat, dryness, and cold. Will get borers like other Robinias.

Landscape Use: Popular in the semiarid West, it differs from R. pseudoacacia in having beautiful pink flowers and a more open growth habit. Zones 3-8.

Cultivar: 'Idaho'.

Characteristics

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