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Name

Vachellia chiapensis (Safford) Seigler & Ebinger, Phytologia 87:  150.  2005.
syn. Acacia chiapensis Safford, J. Wash. Acad. Sci.  5:  356.  1915.

Synonymy and types

Basionym:  Acacia chiapensis Saff., J. Wash. Acad. Sci.  5: 356.  1915. - TYPE:  MEXICO.  CHIAPAS:  near San Fernando, between Tuxtla and Chicoasén, 12 Jan 1907, G. N. Collins 164 (holotype:  US, F photo).

Formal description

Shrub or small tree to 10 m tall.  Bark  brown or gray, lightly furrowed.  Twigs brown to reddish brown, not flexuous, usually densely puberulent.  Short shoots absent.  Leaves alternate, 100-250 mm long.  Stipular spines usually dark brown to black, symmetrical, terete, straight to slightly reflexed near the apex, stout and inflated, 30-80 x 4-7 mm near the base, usually densely puberulent.  Petiole adaxially grooved, 7-17 mm long, densely puberulent; petiolar glands usually 6 to 13, scattered along the petiole, sessile, columnar to very narrow volcano-shaped, base 0.6-1.2 mm across, apex nearly circular, 0.5-0.8 mm across, densely puberulent.  Rachis adaxially grooved, 90-240 mm long, densely puberulent, a sessile, columnar gland commonly present between most pinna pairs (sometimes absent).  Pinnae 12 to 30 pairs per leaf, 30-70 mm long, 5-12 mm between pinna pairs.  Petiolules 0.5-1.2 mm long.  Leaflets 22 to 50 pairs per pinna, opposite, 0.6-1.1 mm between leaflets, linear, 3-8 x 0.7-1.6 mm, glabrous, lateral veins not obvious, only one vein from the base, base oblique, margins lightly ciliate, apex acute to obtuse; beltian bodies 0.5-0.9 mm long.  Inflorescence a densely flowered globose head, 5-9 mm across, in clusters of 10 to 40 in the axil of slightly reduced leaves, or in clusters of 10 to 40 in the axil of much reduced leaves on axillary branches.  Peduncles 10-35 x 0.6-1.1 mm, glabrous to lightly puberulent.  Involucre 4- lobed, located near the middle of the peduncle, glabrous to puberulent, persistent.  Floral bracts peltate, 0.8-1.5 mm long, apex circular and glabrous, deciduous.  Flowers sessile, pale yellow; calyx 5-lobed, 1.0-1.3 mm long, glabrous; corolla 5-lobed, pale yellow, 1.6-1.9 mm long, glabrous; stamen filaments 2.3-3.7 mm long, distinct; ovary glabrous, on a stalk to 0.1 mm long.  Legume black to dark brown, nearly straight, flattened, not constricted between the seeds, linear, 65-90 x 8-10 mm, coriaceous, reticulately striate, glabrous, eglandular, tardily dehiscent along both sutures; stipe less than 5 mm long; apex narrowing to a very short spine-like beak.  Seeds uniseriate, imbedded in a white pulpy material, light brown, ovoid to ellipsoid, slightly flattened, 4.8-5.9 x 3.0-4.1 mm, smooth; pleurogram oval, 2.5-3.5 mm across.  Flowers in January to May. Chromosome number:  Not determined.

Distribution

Usually rare in dry lowland sites, and along and near watercourses in heavily disturbed vegetation in Chiapas, Oaxaca, and Veracruz, Mexico.

Additional info

Vachellia chiapensis is a marginal host for obligate acacia-ants and can sometimes survive in the absence of ants (Janzen 1974).  Most specimens of this species retain cyanogenic glycosides in the leaves, which probably limits herbivory (Seigler et al. 1978, Seigler & Ebinger, 1987). Low Beltian body production in this species may also indicate that it is a marginal host for acacia-ants.  Beltian bodies of this species are not well developed, and usually occur only on the lower 3 to 9 pairs of leaflets on some of the pinnae.

According to Janzen (1974), Vachellia chiapensis occasionally hybridizes with A. cornigera, and with non-ant-acacias such as V. macracantha. During the present study, no specimens were found that would indicate hybridization involving these species. Hybrids involving V. pennatula and V. chiapensis, however, have been observed (Ebinger and Seigler 1992).

Vachellia chiapensis appears to be most closely related to V. globulifera in its morphology and habit.  These two species are easily separated, V. chiapensis having 6-13 columnar petiolar glands scattered along the petiole, globose inflorescences in clusters of 10 to 40, and the legume has a distinct marginal ridge.  Vachellia globulifera, in contrast, usually has only 3-6 narrow volcano-shaped petiolar glands on the petiole, the globose inflorescences rarely exceed 8 in a cluster, and the legumes lack marginal ridges.  These species are also similar in seed dispersal, seedling ecology, low Beltian body production, and the fact that many leaves on elongated lateral branches are not subtended by swollen spines (Janzen, 1974).

Flowering time

January-May.

Representative specimens

MEXICO:

Chiapas:

Oaxaca:

Tabasco:

Veracruz:

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