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Vachellia barahonensis - short shoot and spines

Vachellia barahonensis - short shoot and spines

Vachellia barahonensis - short shoot and spines

Vachellia barahonensis - petiole

Vachellia barahonensis - multi stem

Vachellia barahonensis - inflor

Vachellia barahonensis - habit

Vachellia barahonensis - fruit

Vachellia barahonensis - flower

Vachellia barahonensis - branch

Vachellia barahonensis - trunk spines

Name

Vachellia barahonensis (Urban & Ekman) Seigler & Ebinger, Phytologia  87:  144.  2005.
syn.  Acacia  barahonensis Urban & Ekman in Urban, Ark. Bot. 22a(8):  29.  1928.

Synonymy and types

Basionym:  Acacia barahonensis Urb. & Ekman in Urb., Ark. Bot.  22a (8): 29.  1928. - TYPE:  DOMINICAN REPUBLIC.  BARAHONA:  between Coueve-en-Haut and Trujín, quaternary calcareous soil, 22 Sep 1926, E. L. Ekman 7043 (holotype:  B destroyed; isotype:  S).

Formal description

Shrub or small tree to 5 m tall.  Bark dark brown to reddish brown to gray, rough; the older branches and the trunks of young trees usually bearing clusters of fusiform to aciculate, straight stipular spines to 70 mm long clustered on short shoots.  Twigs gray to dark reddish-brown, somewhat flexuous, glabrous to puberulent.  Short shoots commonly present above the stipular spines, to 2 mm long, covered with acuminate stipules and old leaf bases.  Leaves alternate, also commonly clustered on the short shoots, 0.1-0.5 mm long.  Stipular spines reddish-brown, becoming gray with age, symmetrical, terete, straight, aciculate, to 20 x 0.9 mm near the base, mostly glabrous.  Petiole adaxially grooved, 0.1-0.5 mm long, sparsely puberulent; petiolar gland solitary, located just below the pinna pair, columnar, 0.3-0.6 mm long, commonly inclined toward the apex of the petiole, apex circular, 0.2-0.4 mm across, glabrous, depressed.  Rachis absent.  Pinnae 1 pair per leaf, 8-20 mm long.  Petiolules 0.6-1.1 mm long.  Leaflets 4 to 11 pairs per pinna, opposite, 1.2-2.6 mm between leaflets, oblong to slightly obovate, 3.0-6.8 x 0.8-2.0 mm, glabrous, lateral veins mostly not obvious, only one vein from the base, coriaceous, base oblique, margins not ciliate, apex obtuse.  Inflorescence a densely flowered globose to slightly subglobose head, 5-7 mm across, in fascicles of 1 to 5 from the short shoots.  Peduncles 4-7 x 0.3-0.5 mm, puberulent.  Involucre 4- to 5-lobed, located 1- 2 mm below the base of the head, lightly puberulent, persistent.  Floral bracts spatulate, 0.5-0.8 mm long, sparsely puberulent, more or less persistent.  Flowers sessile, yellow; calyx 5-lobed, 0.7-1.1 mm long, glabrous; corolla 5-lobed, 1.2-1.6 mm long, glabrous; stamens 30 to 35, stamen filaments 2.2-3.1 mm long, distinct; ovary glabrous, on a stipe to 0.2 mm long.  Legumes dark blackish brown to reddish-brown, straight to slightly curved, elliptic in cross section, constricted between the seeds, linear, 75-110 x 5-6 mm, coriaceous, not striate, glabrous and lustrous, eglandular, dehiscent along the ventral suture; stipe 4-8 mm long; apex narrowing to a acuminate beak with a blunt tip.  Seeds uniseriate, surrounded by a reddish-brown pulp, light to dark brown, ellipsoid, slightly flattened, 4.3-4.8 x 3.0-3.8 mm, smooth; pleurogram oval, 2.1-2.8 mm across.  Flowers in March.  Chromosome number unknown.

Distribution

Restricted to arid dogtooth limestone outcroppings near sea level in Azua, and Pedernales Provinces, Dominican Republic. The known collections represent three distinct populations, one from Isla Beata south of the southern tip of the Barahona Peninsula, another from the Sierra Martín García as it intersects with the Caribbean Sea, and one from a small area south of Oviedo near the southern tip of the Barahona Peninsula.

Additional info

No significant population variation was found with regard to any diagnostic character on the basis of the specimens examined.  Although the specimens available for study were limited, each of the three known populations of this species was adequately sampled.  Its occurrence on very xeric limestone outcroppings with thin soil and high water runoff is thought to be a phenomenon accompanied by physiological adaptations similar to those occurring in the serpentine-adapted species (Major 1988).  The four Hispaniolan taxa of this group (V. barahonensis, V. caurina, V. cucuyo, and V. oviedoensis) may constitute a sister group to those occurring in Oriente Province, Cuba.  Whereas there is only circumstantial evidence for this at the present time, the fact that the center of diversity of this group corresponds to the oldest landform of the Caribbean (the Proto-Greater Antilles, from the Eocene) may be evidence of the antiquity of the V. acuifera group.  Moreover, the division of these species into Cuban and Hispaniolan species may be evidence of the Miocene vicariance event that separated Cuba from Hispaniola (Rosen 1985; Pindell and Barrett 1990, Iturralde Vinent 1982, 1999).

Vachellia barahonensis is a cohesive, well-defined species that is separated from most species of this group by a combination of characters:  the involucre 1-2 mm below the inflorescence, linear fruit 75-100 mm long, oblong to slightly obovate leaflets, 4 to 11 pairs per pinna, and a columnar petiolar gland that is inclined toward the apex of the petiole.  This taxon has many similarities to two other Hispaniolan species (V. caurina and V. cucuyo), with which it shares the columnar petiolar gland.  It is distinguished from V. caurina by its upright habit (V. caurina is a sprawling shrub), stipular spines that are mostly more than 10 mm long (less than 6 mm in V. caurina), and the larger leaflets that are more than 1.2 mm apart on the pinna.  It is separated from V. cucuyo, which has two pairs of pinnae on some leaves, and shorter and thicker fruits.  All 11 specimens of this species tested were strongly cyanogenic.

Representative specimens

DOMINICAN REPUBLIC:

Azua Province:

Pedernales Province:

 

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