Monographs Details: Acacia
Authority: Isley, Duane. 1973. Leguminosae of the United States: I. Subfamily. Mimosoideae. Mem. New York Bot. Gard. 25 (1): 1-152.
Description:Genus Description - Armed or unarmed trees or shrubs, rarely herbs. Leaves alternate and often (native species) clustered from spurs; bipinnate or (introduced Australian species) reduced to simple phyllodia; leafstalk usually gland-bearing; pinnae 1-many pairs; leaflets often small and numerous; phyllodia diverse in shape, commonly with a marginal gland at base of blade. Stipular spines borne by most native species, a few with internodal prickles or unarmed; phyllode-bearing species rarely armed. Stipules, if not spiny, small and deciduous. Primary inflorescences yellow to whitish-yellow heads or spikes, pedunculate from spurs or leaf axils and solitary or fasciculate, or in axillary racemes, or, the racemes in varying degrees, terminally aggregated into fasciculate, compound racemes. Perianth 4-5-merous; calyx campanulate, lobed; corolla short-tubular, lobed ca length; stamens numerous, free; ovary sessile to stipitate. Legumes diverse, dehiscent in most to tardily dehiscent or indehiscent, usually oblong to linear, flat to turgid, straight to curved, often irregularly constricted to moniliform; valves thin or thick, membranous to woody in some species, twisting after separation. Funiculus-aril conspicuous in Australian introduced species, the funiculus short and terminally clavate, or elongate, plicate, even completely encircling the seed.
Discussion:Acaciella Britt. & Rose
Acaciopsis Britt. & Rose
Lucaya Britt. & Rose
Tauroceras Britt. & Rose
Vachellia Wight & Arn.
One of the larger genera of flowering plants with perhaps 600 species (“about 900” fide Hutchinson, 1964), most numerous in Australia, tropical Africa, and tropical America. U.S. native kinds primarily of extreme south, Florida to California (A. angustissima to Missouri), most diverse in Texas; introduced species predominantly of urban California.
CBN x = 13.
Literature (native species only): Britton & Rose (1928), Turner (1959), Isely (1969), Correll & Johnston (1970).
The acacias native to the United States are mostly northern outliers of Mexican and Antilles species. They were fragmented by Britton and Rose (1928) into a number of genera on the basis of pod conformation, a judgement that has largely been disavowed by posterity. I have previously reviewed the native kinds in some detail (Isely, 1969).
The economic role of native Acacia is limited. In Texas where they are diverse and common, some have value as browse and honey plants (Graham, 1941; Correll and Johnston, 1970). The overwhelmingly abundant sorts, such as A. berlandieri of southern Texas, do much to render the visual character of the landscape. Many, as the fiercely prickly A. greggii, are primarily regarded by ranchers as weeds.
The majority of species of Acacia in this country are those cultivated in California where they are among the common, ornamental trees and shrubs both in private and public plantings. These, mostly Australian, a few African, Asian, and tropical American, thrive in this state. They are rapid-growing, highly attractive in flower or interesting for their foliage. They are diverse as to size, growth form, texture, and color, and thus fit a variety of roles in landscape design. Acacias also have been introduced into Florida but are less successful than in the Mediterranean climate of the West coast. My introductory remarks have presented a working definition of the term “cultivated” under which 35 species of Acacia are eligible for description in the pages following.
Since I have not previously reported on cultivated Acacia and in view of special problems attendant on their study, a preliminary note on background and mode of treatment is necessary.