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Name

Vachellia melanoceras (Beurling) Seigler & Ebinger, Phytologia 87:  163.  2005.
syn. Acacia melanoceras Beurling, Kongl. Svenska Vetensk. Acad. Handl.  1854:  123.  1856.

Synonymy and types

Basionym:  Acacia melanoceras Beurl., Kongl. Svenska Vetensk. Acad. Handl.  1854: 123.  1856.  Myrmecodendron melanoceras (Beurl.) Britton & Rose, N. Amer. Fl.  23: 93.  1928. - TYPE:  PANAMA.  COLÓN:  Portobello, sea level, Apr 1826, J. G. Billberg 289 [lectotype, designated by Seigler and Ebinger (1995):  S, F photo, MO photo].

Acacia multiglandulosa Schenck, Repert. Spec. Nov. Regni Veg. 12: 362.  1913. - TYPE: PANAMA.  COLÓN:  Portobello, J. G. Billberg 1825 [lectotype, designated by Seigler and Ebinger (1995):  US photo (B, destroyed)].

Formal description

Tree to 15 m tall.  Bark not seen.  Twigs dark brown to dark reddish brown, not flexuous, puberulent.  Short shoots absent.  Leaves alternate, 150-300 mm long.  Stipular spines dark reddish brown to black, symmetrical, terete, straight, stout and inflated below but abruptly tapering to a narrow, sharp-pointed tip, grooved and with low, rounded longitudinal ridges, (rarely with two narrow, blade-like longitudinal flanges), 20-55 x 5-9 mm near the base, glabrous to lightly puberulent; many spines not enlarged, these less than 5 mm long and 0.4 mm wide.  Petiole adaxially flattened, (5)10-28 mm long, densely puberulent; petiolar glands 6 to 30, located on the flattened adaxial surface near the petiole base, sessile, columnar to narrow volcano-shaped, base 0.4-1.5 mm across, apex circular, 0.3-1.1 mm across, puberulent and striated.  Rachis adaxially grooved, 130-280 mm long, puberulent, a sessile, columnar to narrowly volcano-shaped gland between each pinna pair.  Pinnae 12 to 28 pairs per leaf, 20-50 mm long, 6-11 mm between pinna pairs.  Petiolules 0.5-1.2 mm long.  Leaflets 12 to 29 pairs per pinna, opposite, 1.0-1.6 mm between leaflets, linear, 4.5-7.6 x 1.0-1.7 mm, glabrous, lateral veins not obvious, only one vein from the base, base oblique, margins usually not ciliate, apex acute; beltian bodies 1.0-1.6 mm long.  Inflorescence a densely flowered globose head, 5.0-6.5 mm across, solitary or in clusters of 2 to 6 in the axil of small spines on axillary, usually leafless branches to 350 mm long.  Peduncles 5-10 x 0.5-0.8 mm, densely puberulent.  Involucre 5-lobed, located near the base of the peduncle, puberulent, persistent.  Floral bracts peltate, 0.2-1.2 mm long, apex circular and ciliate, deciduous.  Flowers sessile, pale yellow; calyx 5-lobed, 0.9-1.1 mm long, glabrous; corolla 5-lobed, 1.5-1.8 mm long, glabrous; stamen filaments 1.5-2.6 mm long, sometimes fused for about one half their length; ovary glabrous, subsessile.  Legumes dark brown to black, slightly curved, particularly at the narrowing apex, nearly terete in cross section, not constricted between the seeds, oblong, 65-110 x 10-20 mm, coriaceous, reticulately striate, glabrous, eglandular, indehiscent; stipe absent; apex narrowing and usually acuminate.  Seeds uniseriate to irregularly arranged, imbedded in a light brown pulpy material, dark brown, ovoid, slightly flattened, 8.6-10.5 x 5.8-8.0 mm, smooth; pleurogram elliptic to U-shaped, 5.3-6.5 mm across. Flowers in April to July.  Chromosome number:  Not determined.

Distribution

Wet, relatively undisturbed forests on the Atlantic lowlands of central Panama (Colon Province), and the Canal Zone.

Additional info

Vachellia melanoceras has the most restricted range of all ant-acacias and is relatively rare throughout this range.  According to Janzen (1974), rarely more than two individuals are found per hectare in forest communities.  Also, this species, which is usually restricted to lowland wet forests, disappears from any habitat subjected to disturbances that are any more catastrophic than infrequent cutting.

This species can easily be distinguished from all other ant-acacias by the extremely high number (6 to 30) of volcano-shaped petiolar glands on the flattened adaxial surface of the petiole.  Also, the large leaves (to 300 mm) and the rachis glands at the node of each pinna pair help to separate it from most other ant-acacias.

Beltian body production is relatively low in Vachellia melanoceras, rarely more than half of the leaflets on mature plants producing these structures.  This characteristic, which is typical of most wet forest ant-acacias, is probably due to the high cost to the plant of Beltian bodies in a habitat with low solar energy input and perhaps somewhat reduced herbivore loads (Janzen, 1974).  None of the individuals of this species tested positive for cyanide production (Seigler and Ebinger 1995).

Flowering time

April-July.

Representative specimens

PANAMA:

Colón:

Canal Zone:

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