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Name

Vachellia astringens (Gillies) Spegazzini, Bol. Acad. Nac. Ci. Córdoba.  26:  278.  1924.
syn.  Acacia atramentaria Bentham, London Jour. Bot. 1:  392.  1842.

Synonymy and types

Prosopis astringens Gillies in Hook. & Arn.  Bot. Misc.  3: 204.  1833.  Acacia atramentaria Benth., London J. Bot. 1: 392.  1842.  Acacia farnesiana  (L.) Willd. nov.  atramentaria (Benth.) Kuntze, Revis. gen. pl. 3(2): 47.  1898.   (based on same type).  - TYPE:  ARGENTINA.  Mendosa and San Juan, J.Gillies s.n. (holotype:  GL; isotype:  K).  NOTE:  Not Acacia astringens A. Cunn. ex G. Don (1832), a species with phyllodes native to Australia and a synonym of Acacia falciformis DC. (Maslin, 2001a).  Not Acacia adstringens Mart. in Spix and Martius (1828), an unarmed species of legume from Brazil that is not aVachellia.

Acacia prosopoma O. Schnyd., Anales Soc. Ci. Argent. 3: 152.  1877. - TYPE:  none cited, from Argentina, Mendoza, Córdoba.

Formal description

Shrub or small, flat-topped tree to 12 m tall.  Bark dark gray, furrowed.  Twigs dark purplish brown, slightly flexuous and stout, glabrous to lightly puberulent.  Short shoots commonly present above the stipular spines, to 6 m long, covered with acuminate stipules and old leaf bases.  Leaves alternate, also commonly clustered on the short shoots, 15-50 mm long.  Stipular spines dark reddish brown, becoming dark gray with age, symmetrical, terete, straight, stout, to 10 x 1.5 mm near the base, glabrous to rarely puberulent at the base.  Petiole adaxially grooved, 4-11 mm long, puberulent to rarely glabrous; petiolar gland solitary, located at or just below the lower pinna pair, sessile, circular, 0.3-0.8 mm across, doughnut-shaped, usually puberulent.  Rachis adaxially grooved, 10-40 mm long, pubescent with short erect hairs, a sessile, circular gland, 0.2-0.5 mm across present between the upper pinna pair.  Pinnae 2 to 8 pairs per leaf, 13-26 mm long, 4-8(10) mm between pinna pairs.  Petiolules 1.0-2.1 mm long.  Leaflets 14 to 32 pairs per pinna, opposite, 0.6-1.3 mm between leaflets, oblong, 1.8-4.0 x 0.6-0.9 mm, mostly glabrous (rarely lightly pubescent beneath), lateral veins rarely obvious, only one vein from the base, base oblique, margins usually ciliate, apex acute.  Inflorescence a densely flowered globose head, 5-9 mm across, mostly in clusters of 2 to 5 on the short shoots.  Peduncles 20-35 x 0.3-0.6 mm, pubescent with short hairs.  Involucre 4- to 5- lobed, located at the base of the globose head, glabrous to lightly puberulent, persistent.  Floral bracts spatulate, 0.8-1.2 mm long, ciliate, deciduous.  Flowers sessile, pale yellow; calyx 5-lobed, 1.0-1.4 mm long, glabrous; corolla 5-lobed, 2.0-2.6 mm long, glabrous; stamen filaments 3.5-5.5 mm long; distinct ovary puberulent, on a stipe to 0.3 mm long.  Legumes dark brown to black, straight to slightly curved, flattened, not constricted between the seeds, linear, 65-110 x 8-14 mm, coriaceous, usually reticulately striate, puberulent and with scattered long hairs, eglandular, indehiscent; stipe absent; apex acute to obtuse.  Seeds uniseriate, imbedded in white pulpy material, dark brown, ovoid to ellipsoid, slightly flattened, 5.5-8.0 x 4.6-6.1 mm, smooth; pleurogram oval, 3-5 mm across.  Flowers in August to December. Chromosome number:  Not determined.

Distribution

Shrubby vegetation of pasture, successional fields, edge of roads, and scrub-thorn forests from sea level to 1800 m throughout northern Argentina.  This taxon should be expected in adjacent Bolivia and Paraguay.

Additional info

Vachellia astringens (syn. Acacia atramentaria) occurs in the same general habitat as V. caven, disturbed thorn -scrub forests, where V. caven is the more common taxon.  The most distinctive characteristic separating this taxon from other species of acacia in South America, is the sessile, doughnut-shaped petiolar gland between the lower pinna pair, a characteristic it shares with V. schaffneri of North America.

On a few herbarium sheets, James Aronson suggested that V. astringens (syn.  A. atramentaria) and V. caven occasionally hybridize (Aronson 7906, 7910, 7911 from San Luis, Argentina).  It is possible that these specimens represent hybrids as the fruits are essentially elliptical in cross section, and a little wider and thicker than is typical of V. astringens.  Only a small amount of pulpy material is present in the fruits, and the seeds are in a single row, traits of V. astringens.  Vegetative characteristics are within the range of those for V. astringens, including the doughnut-shaped petiolar gland between the lowest pair of pinnae.  A final determination of hybridization must await additional field studies and material.

Of the more than 40 specimens of this species tested for the presence of cyanogenic compounds, nearly 25% gave a strongly positive test within two hours.  Most of these positive tests were from recently collected specimens, indicating that the cyanogenic glycoside or the degradative enzyme deteriorated due to prolonged storage.  Seigler et al. (1979) reported that this taxon was strongly cyanogenic, and later (Seigler et al. 1983) determined that proacacipetalin was the glycoside responsible.  Aronson and Nash (1989) and Aronson (1990) also reported that V. astringens was cyanogenic.

Flowering time

August-December.

Representative specimens

ARGENTINA:

Córdoba:

Corrientes:

Entre Ríos:

Formosa:

Gran Chaco:

Misiones:

Salta:

Santa Fe:

San Luis:

Tucumán:

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