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Name

Vachellia curvifructa (Burkart) Seigler & Ebinger, Phytologia 87:  155.  2005.
syn. Acacia curvifructa Burkart, Las Leguminosas Argentinas, 2nd. ed.  97, 541. 1952.

Synonymy and types

Basionym:  Acacia curvifructa Burkart, Las Leguminosas Argentinas, 2nd ed., 97, 541,  1952. - TYPE:  PARAGUAY.  CHACO:   Puerto Casado, Dec 1916, T. Rojas 2138  (holotype:  SI).

Formal description

Shrub or small tree to 4 m tall.  Bark not seen.  Twigs dark reddish to purplish brown, slightly flexuous, usually lightly puberulent.  Short shoots commonly present above the stipular spines, to 6 mm long, covered with acuminate stipules and old leaf bases.  Leaves alternate, also commonly clustered on the short shoots, 9-35(45) mm long.  Stipular spines reddish brown, becoming light gray with age, symmetrical, terete, straight, stout, to 25(45) x 2.2(3.3) mm near the base, puberulent.  Petiole adaxially grooved, 2-10 mm long, puberulent; petiolar gland solitary, located near the middle of the petiole, sessile, circular to elongated, 0.5-1.0 mm long, apex depressed, usually puberulent.  Rachis adaxially grooved, 0-35 mm long, usually densely puberulent, a sessile, circular gland, 0.3-0.5 mm across between most pinna pairs.  Pinnae 1 to 4(5) pairs per leaf, 6-15 mm long, 1.5-10.5 mm between pinna pairs.  Petiolules 0.9-2.1 mm long.  Leaflets 8 to 17 pairs per pinna, opposite, 0.9-1.5 between leaflets, oblong, 2.5-5.1 x 0.6-1.3 mm, mostly puberulent, sometimes densely so, lateral veins very obvious, only one vein from the base, base oblique, margins ciliate, apex acute.  Inflorescence a densely flowered globose head, 5-7 mm across, solitary or in clusters of 2 to 3 on the short shoots.  Peduncles 5-20 x 0.5-0.8 mm, puberulent.  Involucre 5-lobed, located at the base of the globose head, puberulent, persistent.  Floral bracts spatulate, to 1.0-1.8 mm long, puberulent, deciduous.  Flowers sessile, pale yellow; calyx 5-lobed, 1.0-1.4 mm long, the lobes puberulent; corolla 5-lobed, 1.6-2.0 mm long, the lobes puberulent; stamen filaments 2.0-3.5 mm across distinct; ovary glabrous to densely puberulent, on a stipe to 0.2 mm long.  Legumes dark brown to black, strongly curved, flattened to slightly elliptical in cross section, not constricted between the seeds, linear, 25-60 x 9-13 mm, coriaceous, reticulately striate, puberulent, eglandular, indehiscent; stipe absent, apex acute.  Seeds uniseriate, no pulp, light to dark brown, ovoid, slightly flattened, 5.2-6.6 x 3.0-4.1 mm, smooth; pleurogram U-shaped to nearly oval, 1.5-3.0 mm across. Flowers in June to November. Chromosome number:  Not determined.

Distribution

Thorn-scrub forests in the chaco of Paraguay and northern Argentina.

Additional info

From the information available on the herbarium sheets, this species occupies the same habitat as that of Vachellia caven, scrubby woodlands, thorn-scrub forests and other xeric sites in the Chaco of Argentina and Paraguay.  The curved, flattened fruit of V. curvifructa, which is densely puberulent and with a single row of seeds, is quite different from the mostly straight, glabrous, inflated fruits of V. caven in which the seeds are in several rows and imbedded in a sweet pulp.  The puberulent leaflets in which the secondary veins are obvious also separate this species from V. caven. 

It has been suggested that this taxon is a putative hybrid between Vachellia caven and V. farnesiana (Aronson and Nash 1989).  Present information suggests that V. farnesiana is not common in Argentina or Paraguay; being present as scattered introductions.  Vachellia curvifructa is similar to V. farnesiana in that it has relatively large leaflets with obvious secondary venation; the structure of the petiolar gland, the puberulent petioles, rachis, and the short peduncles may indicate a relationship to V. caven.  The only other related species in this part of South America is V. astringens (syn. V. atramentaria), but no specimens of this species have been found in Paraguay.  The petiolar gland of V. astringens is quite distinct from that found in V. curvifructa, being donut-shaped and located between the pinnae of the lowest pinna pair.  Of the 25 specimens of this species examined for cyanogenic glycosides, none tested positive.  Aronson and Nash (1989) reported cyanogenesis in two specimens of this taxon.

Flowering time

June-November.

Representative specimens

ARGENTINA:

Formosa:

Salta:

PARAGUAY:

Boquerón:

Presidente Hayes:

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