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Name

Vachellia allenii (D. H. Janzen) Seigler & Ebinger, Phytologia 87: 142.  2005.
syn.  Acacia allenii D. H. Janzen, Smithsonian Contr. Bot.  13:  53.  1974.

Synonymy and types

Basonym:  Acacia allenii D.H. Janzen, Smithsonian Contr. Bot. 13: 53.  1974. - TYPE:  COSTA RICA.  PUNTARENAS:  Osa Peninsula, bank of tributary of Río Agua Buena, 3.5 mi. SW of Rincón, 9 Mar l967, D. H. Janzen 1769 (holotype:  US; isotypes: F, GH, K, MEXU, MICH, MO, NY, UC).

Formal description

Tree to 25 m tall.  Bark not seen.  Twigs dark brown to dark reddish brown, not flexuous, lightly puberulent.  Short shoots absent.  Leaves alternate, 150-450 mm long.  Stipular spines black to dark brown, symmetrical, nearly terete, straight to slightly reflexed, stout and inflated, commonly grooved and with low, rounded longitudinal ridges, 20-45 x 8-12 mm near the base, glabrous to lightly puberulent.  Petiole adaxially grooved, 14-30(45) mm long, lightly puberulent; petiolar glands usually 4 to 10, scattered along the petiole, sessile, narrowly volcano-shaped,  base 0.8-1.2 mm across, apex nearly circular, 0.4-0.7 mm across, puberulent and lightly striate.  Rachis adaxially grooved, 20-400 mm long, lightly puberulent, 1 or 2 sessile, narrowly volcano-shaped glands located between each pinna pair and sometimes scattered along the rachis between the pinna pairs.  Pinnae 10 to 22 pairs per leaf, 60-110 mm long, 15-22 mm between pinna pairs.  Petiolules 1.3-2.6 mm long.  Leaflets 15 to 25 pairs per pinna, opposite, 2.0-3.2 mm between leaflets, oblong, 6-12 x 1.8-3.9 mm, glabrous, lateral veins obvious, 2 to 3 veins from the base, base oblique, margins usually not ciliate, apex obtuse to rarely acute; beltian bodies 1.5-3.0 mm long.  Inflorescence a densely flowered globose head, 5-7 mm across, in clusters of 5 to 15 in the axil of reduced leaves on axillary branches 40-150 mm long.  Peduncles 10-15 x 0.6-0.9 mm thick, lightly puberulent.  Involucre 5-lobed, located on the lower third of the peduncle, puberulent, persistent.  Floral bracts peltate, 0.8-1.0 mm long, apex circular and ciliate, deciduous.  Flowers sessile, pale yellow; calyx 5-lobed, 0.9-1.2 mm long, puberulent on the lobes; corolla 5-lobed, 1.2-1.5 mm long, glabrous; stamen filaments 1.6-2.1 mm long, distinct; ovary glabrous, subsessile.  Legumes dark brown to black, slightly curved, elliptical in cross section, not constricted between the seeds, linear, 65-110 x 15-20 mm, coriaceous, reticulately striate, glabrous, eglandular, dehiscent along both sutures; stipe absent; apex acute.  Seeds uniseriate, imbedded in a yellowish pulpy material, dark brown, slightly flattened, 12.5-16.0 x 6.5-8.5 mm, smooth; pleurogram elliptic, 3.5-4.5 mm across.  Flowers in April to July. Chromosome number:  Not determined.

Distribution

Heavily shaded understory at lower elevations (to 800 m) in wet forests, in moist disturbed stream banks, at forest edge, and on roadsides, in Puntarenas Province, Costa Rica (Janzen 1974).

Additional info

The narrow geographic range of Vachellia allenii is typical of many of the ant-acacia species of Central America. Its normal habitat appears to be at lower elevations in heavily shaded understory of wet tropical forests.  In general, this species reacts fairly well to disturbances, and most present-day collections are from roadsides, recent landslides, disturbed stream banks, and secondary successional areas after logging.  It is rarely found in open pastures, and according to Janzen (1974) will not survive fire.

As is typical of many wet forest ant-acacias, Beltian body production in Vachellia allenii is not particularly extensive.  However, the Beltian bodies are much larger (to 3 mm long) than those found on dry area ant-acacias.  In V. allenii, these relatively large Beltian bodies are formed only on the lower 3 to 6 leaflets of each pinna and occasionally the lower leaflet of a pinna has been replaced by a large Beltian body.  None of the individuals gave a positive test for cyanide production.

Vachellia allenii is most closely related to V. melanoceras from which is easily separated by its leaflets which are nearly twice as large and have obvious secondary veins.  Also, well-developed leaves of V. allenii have only 4-10 widely scattered petiolar glands, whereas those of V. melanoceras commonly have 6-30 closely-spaced petiolar glands on the flattened adaxial surface of the petiole.  Furthermore, the fertile branches of V. allenii are commonly less than 150 mm long, are scattered along major branches throughout the crown, and have 5 to 15 inflorescences in the axis of reduced leaves.  In V. melanoceras, the fertile branches are to 350 mm long, tend to be bunched near the ends of the branches, and have 2 to 6 inflorescences at each node.

Flowering time

April-July.

Representative specimens

COSTA RICA: 

Puntarenas: 

San José: 

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