Shrubs or trees, some species nearly herbaceous, with bipinnate leaves, the ultimate leaflets usually small and numerous, or the leaves in many exotic species modified into flat simple phyllodes. Flowers small, in heads or spikes. Calyx campanulate, usually 4-5-toothed, or of 4 or 5 distinct sepals. Petals mostly 4 or 5, separate, united, or wanting. Stamens , exserted; filaments filiform, separate; pollen-grains cohering in 2's-6's. Ovary sessile or. stipitate. Pod linear, oblong or oval, flat or swollen, often constricted between the seeds. [Greek, point, or thorn, many species being thorny.]

Perhaps 300 species, chiefly in subtropical regions, most abundant in Africa and Australia, a few in the temperate zones. Besides the following, several others occur in the southern United States. Type species: Mimosa scorpioides L.

1. Acacia Angustissima (Mill.) Kuntze. Prairie Acacia

Fig. 2429

Mimosa angustissima Mill. Gard. Dict. Ed. 8, no. 19.

1768. Mimosa filiculoides Cav. Ic. 1: 55. pl. 78. 1791. Acacia filicina Willd. Sp. Pl. 4: 1072. 1806. Acacia filiculoides Trelease; Branner & Coville, Rep.

Geol. Surv. Ark. 1888: Part 4, 178. 1891. A. angustissima Kuntze, Rev. Gen. Pl. 32: 47. 1898.

A low thornless shrub, varying from glabrous to hirsute-pubescent. Pinnae of the leaves 2-15 pairs, oblong in outline, 1'-2' long; leaflets 10-50 pairs, oblong or linear-oblong, about 2" long, less than 1" wide, obtuse or acute, slightly inequilateral, 1-veined; heads globose, many-flowered, axillary, slender-peduncled, 6"-10" in diameter; sepals distinct or nearly so; filaments yellow, 3-4 times as long as the sepals; pod linear, acute, often narrowed at the base, stipitate, mostly straight, 1'-2' long, about 3" wide, flat, its valves thin, reticulated, glabrous or pubescent, impressed between the seeds.

Prairies, plains and bluffs, Missouri and Kansas to Texas, Arizona and Mexico. May-July.

1 Acacia Angustissima Mill Kuntze Prairie Acacia 771