The Black Locust - Robinia pseudoacacia

The Black Locust - Robinia pseudoacacia,  is most easily recognized by the combination of hanging clusters of creamy white flowers, pinnate leaves subtended by a pair of sharp pointed spines and coarse ridged or furrowed blackish or deep brown bark.  

Image Citation: Chris Evans, University of Illinois, Bugwood.org

Black Locust is established in the moist woods, stream margins, river bottoms and Mountains in most of the United States, the Southern most portions of Canada and some parts of Europe.  Believed to have a native range from the Southern Appalachian to the Ozark Mountains.  Similar in appearance to the Clammy Locust and Bristly Locust, with their only difference being flower colors of pink to rose-purple. 

Image Citation: Norbert Frank, University of West Hungary, Bugwood.org

The Black Locust is a deciduous tree that can reach heights of 75 feet tall in ideal conditions. Generally forming a single straight trunk, open irregular crown and ascending branches.  Occasionally taking on a spreading form when grown out in the open. The bark is dark in color ranging from gray to dark gray-brown or dark brown to black, with coarse ridges or deep furrows.  The leaves are alternate, pinnate, with blades ranging from 20-36 cm long and 4-12 cm broad.  The petiole averages about 3 cm long and is subtended by a pair of sharp pointed spines (thorns).  Leaflets occur in numbers of 7-25 generally in odd numbers, thin and elliptic in shape with a rounded or bluntly wedge shaped base, and tipped with small teeth.  The leaf surfaces are medium green to yellow green.  Flowers are bisexual, fragrant and white to creamy white in color with small dull yellow patch on each.  The Calyx is 6-9 mm long, corolla is 1.5-2.5 cm long, produced from the leaf axils in an elongate drooping raceme.  The flowers occur in Spring to early Summer annually.  The fruit is an oblong, flat legume 5-10 cm long and about 1 cm broad.  Fruit matures in late Summer to early Summer annually.

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