_a_ Leaves unequally twice pinnate, 2°—4° long, deciduous; leaflets serrate, 2′—3′ in length; branches and stem armed with scattered prickles. Aralia (p. 778). _aa_ Leaves equally twice pinnate, usually smaller; branches unarmed or armed with stipular or axillary spines (in _Parkinsonia_ often apparently simply pinnate). _b_ Leaflets crenate; leaves simply or twice-pinnate on the same plant, deciduous, usually armed with simple or branched axillary spines. Gleditsia (p. 607). _bb_ Leaflets entire. Leaflets 2—2½′ long; leaves deciduous; branchlets stout, unarmed. Gymnocladus (p. 605). Leaflets smaller; leaves usually persistent; branchlets slender. Branches armed with prickles or spines. Leaves with 2 or rarely 4 pinnæ. Branches armed with axillary spines or spiny rachises. Pinnæ with 4—8 leaflets; branches with short axillary spines. Cercidium (p. 613). Pinnæ with 8—60 leaflets; branches armed with spiny rachises or rigid branchlets terminating in stout spines. Parkinsonia (p. 611). Branches armed with stipular prickles; leaves persistent. Pinnæ with many oblong to linear leaflets. Prosopis (p. 599). Pinnæ with 1 pair of orbicular to broad-oblong leaflets. Pithecolobium unguis-cati (p. 586). Leaves with 6, or more, rarely 4, pinnæ. Prickles usually spreading, often recurved. Acacia (p. 591). Prickles usually more or less ascending, straight. Pithecolobium (p. 586). Branches unarmed. Branchlets and petioles glabrous; leaves with 2—5 pair of pinnæ, each with 40—80 leaflets. Lysiloma (p. 589). Branchlets and petioles pubescent while young; leaves with 5—17 pair of many-foliolate pinnæ, or pinnæ 2—4 and each with 8—16 leaflets. Leucæna (p. 596). *** Leaves simply pinnate.