LEGUMINOSAE 



Black Locust 

 Robinia pseudoacacia L. 



HABIT. A medium-sized tree 40-60 feet high and 1-2 feet 

 in diameter (max. 100 by 5 feet); open, irregular crown. 



LEAVES. Alternate; pinnately compound; 8-14 inches 

 long; with 7-21 ovate-oblong, entire, glabrous leaflets, 1^-2 

 inches long, dark blue-green above and paler below; deciduous. 



FLOWERS. Papilionaceous; perfect; showy; fragrant; in 

 racemes; calyx bell-shaped; corolla 5-petaled, white; stamens 

 10; ovary I -celled; appearing after the leaves. 



FRUIT. A smooth, dark brown, flat, linear-oblong legume, 

 2-4 inches long; containing 4-8 flat brown seeds about ^^e inch 

 long. 



TWIGS. Rather stout; red-brown; armed with stipular 

 spines about Yz inch long. Winter buds: terminal absent, lateral 

 minute, red-hairy, submerged within leaf scar, 3-4 superposed. 



BARK. Red-brown to nearly black; deeply fissured into 

 rounded, scaly ridges. 



WOOD. Moderately important; very heavy and hard; very 

 durable; dark brown or golden; used for posts, ties, and insu- 

 lator pins. 



SILVICAL CHARACTERS. Intolerant; fast growing; se- 

 riously threatened by locust borer {Cyllene robiniae) ; prefers moist, 

 rich soils, but hardy on poor, dry sites; a clan of this species which 

 propagates only by vegetative means is known as Shipmast 

 locust (var. rectissima Raber). 



GENERAL. There are about 20 species of Robinia, all native 

 to North America, with 4 reported to reach tree size. 



These tree species are keyed out below: 



1. Legume, twigs, and peduncle glabrous or nearly so 



R. pseudoacacia L., Black Locust 



1. Legume and peduncle hispid, glandular, or viscid. 



2. Twigs glabrous; usually a shrub; eastern 



R. kelseyi Hutchins, Kelsey Locust 



2. Twigs glandular pubescent or viscid. 



3. Glands not viscid. Southwestern 



R. neo-mexicana A. Gray, New Mexican Locust 



3. Glands exuding a clammy, sticky substance; eastern United 

 States R. viscosa Vent, Clammy Locust 



[283] 



