3. ACACIA Adans.
Trees or shrubs, with slender branches armed with spinescent stipules or infrastipular spines. Leaves alternate on young branchlets and fascicled in earlier axils, bipinnate, with usually small leaflets, persistent. Flowers perfect or polygamous, small, in the axils of minute linear bractlets more or less dilated and often peltate at apex, in globose heads or cylindric spikes on axillary solitary or fascicled peduncles; calyx campanulate, 5 or 6-toothed; petals as many as the divisions of the calyx, more or less united; stamens numerous, usually more than 50, exserted, free or slightly and irregularly united at base, inserted under or just above the base of the ovary; filaments filiform; anthers small, attached on the back, versatile; ovary contracted into a long slender style terminating in a minute stigma. Legume nearly cylindric or flat, indehiscent, continuous or divided within. Seeds transverse, compressed; seed-coat thick, crustaceous, marked on each face of the seed by an oval depression or ring; radicle straight, included, or slightly exserted.
Acacia with more than four hundred species is widely distributed through Australia, where it is most largely represented, tropical and southern Africa, northern Africa, southwestern China, the warmer regions of southern Asia, the islands of the south Pacific, tropical and temperate South America, the West Indies, Central America and Mexico to the southwestern boundaries of the United States where ten or twelve species occur; of these five are arborescent. Acacia is astringent, and many species yield valuable tan bark. Gum arabic is produced by different Old World species; many of the species yield hard heavy durable wood, and some of the Australian Acacias are large and valuable timber-trees. Many species are cultivated for their graceful foliage and handsome fragrant flowers.
The generic name, from ἀκακία, relates to the spines with which the branches are usually armed.
CONSPECTUS OF THE ARBORESCENT SPECIES OF THE UNITED STATES.
Flowers in globose heads; corolla 5-lobed; ovary sessile; stipules persistent, becoming spines. Legume cylindric, glabrous, its sutures conspicuously thickened and grooved; seeds in 2 ranks.1. [A. Farnesiana] (E). Legume flattened, pubescent, its sutures not thickened, slightly grooved; seeds in 1 rank.2. [A. tortuosa] (E). Flowers in short, often interrupted, spikes; legume flattened, pubescent, its sutures thickened; seeds in one rank.3. [A. Emoriana] (E). Flowers in elongated slender spikes; corolla of 5 petals only slightly united at base; ovary stalked; stipules caducous; branchlets armed with infrastipular spines. Legume 1′—1¼′ wide, straight or slightly contracted between the seeds, not becoming twisted and contorted at maturity; seeds narrow-obovoid or ovoid; leaflets green, glabrous, with prominent veinlets.4. [A. Wrightii] (E). Legume ½′—¾′ wide, often conspicuously contracted between the seeds, becoming twisted and contorted at maturity; seeds nearly orbicular; leaflets blue-green, pubescent, with obscure veinlets.5. [A. Greggii] (E, G, H).
1. [Acacia Farnesiana] Willd. Huisache. Cassie.
Leaves 2′—4′ long, with 2—8, usually 4 or 5, pairs of pinnæ, generally somewhat puberulous on the short petiole and rachis; in Texas mostly falling at the beginning of winter; pinnæ sessile or short-stalked, remote or close together, with 10—25 pairs of linear acute leaflets tipped with a minute point, unequal at base, sessile or short-petiolulate, glabrous or puberulous, bright green, ⅛′—¼′ long. Flowers bright yellow, very fragrant, 1/16′ long, opening during the summer and autumn from the axils of minute clavate pilose bractlets, in heads ⅔′ in diameter, on axillary thin puberulous peduncles, solitary or most often 2 or 3 together and 1′—1½′ in length, with two minute dentate connate bracts forming an involucral cup immediately under the flower-head; calyx about half as long as the petals and like them somewhat pilose on the outer surface; stamens two or three times as long as the corolla; ovary short-stipitate, covered with long pale hairs. Fruit oblong, cylindric or spindle-shaped, thick, turgid, straight or curved, slightly contracted between the seeds, short-stalked, narrowed at apex into a short thick point, 2′—3′ long, ½′—⅔′ broad, dark red-purple, lustrous, and marked by broad light-colored bands along the thickened grooved sutures, the outer coat of the walls thin and papery, inclosing a thick pithy pulp-like substance surrounding the seeds, each in a separate thin-walled compartment; seeds ovoid, thick, flattened on the inner surface by mutual pressure, ¼′ long, suspended transversely in 2 ranks on a short straight funicle, light brown, lustrous, and faintly marked by large oval rings.
A tree, 20°—30° high, with a straight trunk 12′—18′ in diameter, separating 6°—8° from the ground into numerous long pendulous branches forming a wide round spreading head, and slender terete or slightly striate angled branchlets, glabrous or at first puberulous, and armed with straight rigid terete spines developed from the persistent stipules and sometimes 1½′ long. Bark of the trunk thin, reddish brown, irregularly broken by long reticulated ridges, exfoliating in large thin scales. Wood heavy, hard, close-grained, rich reddish brown, with thin pale sapwood; in India used for the knees of small vessels and in agricultural implements.