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Project Name Data (Last Modified On 11/15/2012)
 

Flora Data (Last Modified On 11/15/2012)
Genus ACACIA Willd.
PlaceOfPublication Sp. P1. 4:1049. 1806.
Reference Rafinesque (Sylva Tellur. 118-120. 1838)
Synonym Cuparilla, Drepaihyla, Eburnax, Esclerona, Gumi- fera, Hecatandra, Poponax, Senegalia, and Zigmaloba. Britton and Rose segregates (N. Am. Fl. 23:85-96. 1928) include: Acaciella, Acaciopsis, Bahamia, Fishlocizia, Lucaya, Myrme- codendrm, Tauroceras, and Feracacia Britt. & Bro. Leon. Dalla Torre & Harms further list the following synonyms: Arthosprion Hassk.; Chitonanthus Lehm.; Farnesia Gasparr.; Hoopesia Buckl.; Phyllodoce Link; Sassa Bruce ex Gmelin; Tetracheilos Lehm.;Vachellia Wight & Arn.
Description Woody plants, usually armed with scattered thorns or stipular spines. Leaves (Central American species) bipinnate, the pinnae few or many, opposite, the leaf- lets mostly small and numerous; petiole in the majority of species bearing some sort of a gland or glandular field; rachis short or elongate, glandular or less often eglandular; stipules usually small and caducous but sometimes modified as promi- nent spines, in the "bull-horn" species these very large and myrmecophilous. In- florescence basically of axillary, solitary or fasciculate, pedunculate heads, spikes, umbels or racemes, often appearing paniculate because of suppression of leaves at terminal and subterminal, floriferous nodes. Flowers small, usually numerous and dense, predominately whitish or yellowish, normally exceeding the bractlets; calyx usually campanulate, sympetalous, 4- or 5-toothed; corolla typically funnelform, sympetalous for most of its length or in some species 4- to 5-cleft nearly to the base; stamens diagnostic, numerous, free or rarely somewhat united at the extreme base; anthers small, rarely glandular; ovary small, the style and terminal stigma scarcely visible among the stamens. Legume usually oblong to linear, terete or more frequently compressed or flattened, usually straight, dehiscent and with slightly elevated margins, the seeds transverse.
Distribution ropics and subtropics of New and Old Worlds, very prominent in Australia.
Note The genus is highly variable, with many groups of species simulating diverse other genera (parallel evolution) and reflecting environmental adaptation (xero- phytism, etc.). It is thus extremely difficult to give a generalized yet definitive description for the genus (the numerous, free or nearly free stamens being the only binding characteristic), but it is even more difficult to establish clear-cut sub- divisions of or within the genus. Most of the numerous segregates of Acacia, such as those recognized by Britton and Rose (N. Am. Fl. 23:84. 1928), depend upon subjective evaluation (viz.: coriaceous vs. cartilaginous; linear vs. oblong; subterete vs. turgid; promptly vs. tardily dehiscent; etc.). It becomes highly in- convenient with these segregates to determine the "genus," let alone the species, except where perfect material (with fruit) and at least modest familiarity with the group is to be had. Even then many marginal cases exist, where a species may well fall into either of two "genera." Thus, for convenience, if nothing else, I prefer to recognize Acacia in the traditional broad sense, in spite of certain groups of species forming islands within the genus markedly different- from other group- ings of species. The species of Acacia usually present considerable variability and intergrada- tion. It would seem that formulation of species has been unusually inordinate in this genus. When material from Mexico to middle South America is examined and compared, or in areas from which abundant material is available, many specific distinctions fade. This appears especially true in the segregate genera "Acaciella" and "Senegalia" as considered by Britton and Rose. On the other hand, many of the "bull-horn" species, differing but difficult of separation, may prove constant with further collections. Collections of all species in Panama are rather meagre, with the possible exception of species occurring on Barro Colorado Island. It is as yet not possible to study degree of variation of these species within the country, nor to confidently correlate single or few collections with better known Mexican and northern Central American expressions of (presumably) the same entity.
Key a. Flowers pedicellate; petiole eglandular; twigs unarmed ("Acaciella"). b. Leaflets nearly linear (about 6 mm. long and 1 mm. wide), numerous (frequently 60 or more pairs per pinna), subglabrous; twigs com- monly subglabrous-..................................................................... 1. A. ANGUSTISSIMA bb. Leaflets oblong or ovate (usually 8-9 mm. long and at least 2 mm. wide), fewer (9-2 5 pairs per pinna), pubescent; twigs often villous... 2. A.VILLOSA ia. Flowers sessile or subsessile; petiole with 1 or more glands; twigs rarely unarmed. b. Armament of scattered thorns or lacking; flowers whitish (etSenegalia"). c. Flowers in short, oblong spikes, comparatively large ------------------------ 3. A. HAYESII cc. Flowers capitate, small. d. Leaflets relatively large (usually 10 mm. long), more or less oblong, pubescent at least below; thorns frequently lacking .... 4. A. GLOMEROSA dd. Leaflets small (usually 4-6 mm. long), linear or sublinear, glabrous except often ciliate marginally; thorns usually present. e. Costa of leaflet excentric, submarginal; petiolar gland usually solitary; legume glabrous or subglabrous in age .......................... 5. A. TENUIFOLIA ee. Costa of leaflet subcentral, at least apically; petiole frequently bearing 2 glands; legume tomentulose ........................................ 6. A. RIPARIA bb. Armament of paired stipular spines; flowers yellowish. c. Stipular spines slender, usually whitish, solid, not ant-infested; peduncle not involucrate; in A. farnesiana older branchlets with axillary "cushions" or short-shoots, and the leaves small (scarcely 6 cm. long), with few pinnae. d. Leaves less than 6 cm. long, with 2-6 pairs of pinnae ("Vachellia") 7. A. FARNESIANA dd. Leaves usually 10 cm. long or longer, with 8-60 pairs of pinnae ("Poponax"). Not known from Panama outside of cultivation, but to be expected there ....................... 8. A. MACRACANTHA cc. Stipular spines mostly gross, dark, hollow, myrmecophilous; pedun- cle involucrate; leaves large (usually 1 dm. long or longer), with several pinnae ("Myrmecodendron" except no. 12). d. Inflorescence capitate; leaflets with a single prominent vein; leaf rachis glandular. e. Heads axillary; petiole eglandular ................................................ 9. A. COOKII ee. Inflorescence paniculate, the nodes not foliate; petiole bearing few to several glands ......................... ........................... 10. A. MELANOCERAS dd. Inflorescence spicate; leaflets with 2-3 prominent veins; leaf rachis usually eglandular. e. Legume turgid-compressed, dehiscent (often tardily), short- beaked, the pericarp thick; spike thin (about 3 mm. thick), without protruding bractlets; petiolar gland of 2-3 crateri- form nectaries ........-.......................................................... II. A. COSTARICENSIS ee. Legume terete, indehiscent, long-beaked, the pericarp thin; spike stout (almost 1 cm. thick), with protruding bractlets; petiolar gland with a solitary, crateriform nectary ("Tauro- ceras"). To be expected in Panama- .........................-.... . 12. A. SPADICIGERA
 
 
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