Deciduous trees or shrubs. Twigs often prickly, more or less angled, zigzag; pith round, continuous. Buds small, superposed, covered by the leaf-scar; terminal bud lacking. Leaf-scars alternate, broadly triangular, consisting of a membrane that later splits open, revealing the buds; bundle-traces 3; stipules modified as bristles or prickles which enlarge and persist for several years.

Fig. 172. Robinia pseudo acacia

Fig. 172. Robinia pseudo-acacia.

a.

Twigs glabrous or nearly so

1.

R. pseudo-acacia

a.

Twigs bristly, glandular or viscid

2.

R. viscosa

1. R. pseudo-acacia L. Black Locust. A tree to 25 m.high, but generally smaller; bark rough, deeply furrowed, dark brown; twigs moderate, somewhat zigzag, greenish to reddish-brown, usually with two stipular spines at each node; pods dark brown, 5-10 cm. long,10-12 mm. wide, often remaining on trees through the winter. Woods and thickets, Georgia to Louisiana, north to Pennsylvania, Indiana, and Oklahoma, now widely introduced and naturalized (Fig. 172).

2. R. viscosa Vent. Clammy Locust. A small tree, to 12 m. high, with dark red-brown glandular-viscid twigs; stipular spines small or lacking; pods clammy. Dry woods, in the mountains, North Carolina to Georgia and Alabama; cultivated northwards.