Vachellia guanacastensis

Vachellia guanacastensis

Vachellia guanacastensis

Vachellia guanacastensis

Vachellia guanacastensis

Vachellia guanacastensis - habit

Vachellia guanacastensis - leaves


Vachellia guanacastensis (Clarke, Seigler & Ebinger) Seigler & Ebinger, Phytologia 87:  159.  2005.
syn.  Acacia guanacastensis (Clarke, Seigler & Ebinger) Ebinger & Seigler, Syst. Bot. 25:  610.  2000.

Synonymy and types

Basionym:  Acacia farnesiana (L.) Willd. var. guanacastensis Clarke, Seigler & Ebinger, Syst. Bot.  14: 562.  1989.  Acacia guanacastensis (Clarke, Seigler & Ebinger) Ebinger & Seigler Syst. Bot.  25: 610.  2000. - TYPE:  COSTA RICA.  GUANACASTE:  Great Swamp, Comelco, near Bagaces, 11 May 1976, D. H. Janzen 10362 (holotype:  MO; isotype:  ILL).

Formal description

Shrub or small tree to 5 m tall.  Bark dark gray to brown, shallowly furrowed.  Twigs dark purplish brown to dark brown, slightly flexuous, pubescent with erect hairs.  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, 15-60 mm long.  Stipular spines light to dark brown to purplish brown, sometimes becoming light gray with age, symmetrical, terete, straight, stout, to 25(35) x 2 mm near the base, pubescent with erect hairs.  Petiole adaxially grooved, 4-8 mm long, densely pubescent with erect hairs; petiolar gland solitary, located near the middle of the petiole, sessile, circular to elongated on the primary leaves, 0.2-1.1 mm long, apex depressed, glabrousRachis adaxially grooved, 10-50 mm long, densely pubescent with erect hairs, a sessile, circular gland, 0.4-0.7 mm across between the upper 1 to 2 pinna pairs.  Pinnae 3 to 9 pairs per leaf, 15-28 mm long, 3-8 mm between pinna pairs.  Petiolules 0.9-1.6 mm long.  Leaflets 16 to 30 pairs per pinna, opposite, 0.6-1.0 between leaflets, oblong, 3.0-5.1 x 0.8-1.1 mm, lightly pubescent beneath, lateral veins usually not obvious, only one vein from the base, base oblique, margins ciliate, apex obtuseInflorescence a densely flowered globose head, 6-10 mm across, in small clusters of 2 to 5 on the short shoots.  Peduncles 14-26(30) x 0.4-0.7 mm, densely puberulent.  Involucre 4- to 6- lobed, located at the base of the globose head, puberulent, persistent.  Floral bracts spatulate, 1.3-1.5 mm long,  puberulent, deciduous.  Flowers sessile, yellow; calyx 5-lobed, 1.3-1.7 mm long, the lobes puberulent; corolla 5-lobed, 1.9-2.5 mm long, the lobes puberulent; stamen filaments 3.5-5.5 mm long, distinct; ovary glabrous, on a stipe to 0.2 mm long.  Legumes dark brown to black, straight to slightly curved, nearly terete in cross section, slightly constricted between some of the seeds, oblong, 70-150 x 9-13 mm, coriaceous, strongly reticulately striate, puberulent, glandular,  dehiscent; stipe to 7 mm long; apex acuminate and mucronate.  Seeds uniseriate to rarely weakly biseriate, imbedded in a white pulpy material, light to dark brown, ellipsoid to ovoid, slightly flattened, 6.8-9.2 x 5.0-7.2 mm, smooth; pleurogram U-shaped, 3-4 mm across. Flowers intermittently throughout the year. Chromosome number:  Not determined.


On seasonally dry sites in thickets, open pastures, rocky hillsides, savannas, successional fields and other disturbed sites from sea level to about 500 m from southern Mexico (Oaxaca and Veracruz) throughout Central America to Venezuela. This taxon is probably adventive in South America.

Additional info

Vachellia guanacastensis is variable in some of its characteristics, particularly the number of pinna pairs and the number of leaflets per pinna.  This variation, however, is due to the presence of both short shoot leaves and primary leaves.  As with all members of the Vachellia farnesiana group, short shoots are present just above the stipular spines.  In V. guanacastensis, the leaves of the short shoots are smaller than the (primary) leaves that develop between the stipular spines.  These short shoot leaves generally have smaller, round petiolar glands, usually only 3-6 pairs of pinnae, whereas the pinnae are 15-20 mm long and have 16-22 pairs of leaflets.  The primary leaves are larger with slightly elongated, larger petiolar glands, 7-9 pairs of pinnae that are longer and contain more than 20 pairs of leaflets.  On both the short shoot leaves and the primary leaves, the petioles and the leaflets are essentially the same size.

Vachellia guanacastensis is easily separated from V. farnesiana and V. tortuosa, the other taxa of this species group in the region (southern Mexico, Central America and Venezuela). The best characters for consistent separation are the 7-9 pairs of pinnae, pinnae with more than 20 pairs of leaflets, and the pubescent leaves of V. guanacastensis.  Both V. farnesiana and V. tortuosa have fewer pinnae and leaflets, and the leaflets are mostly glabrous.  Fruit characteristics also can be used to separate these three species.  Vachellia guanacastensis fruits are similar to V. farnesiana in being more than 9 mm thick, nearly terete and inflated; however, the fruits are usually longer and pubescent, similar to V. tortuosa.  Vachellia tortuosa, however, has narrower fruits that are constricted between the seeds.  The fruits of V. guanacastensis differ from both of these taxa in having thin septae between the seeds.

Sousa and Rico (unpublished data) suggested that this taxon is of hybrid origin involving V. farnesiana and V. schaffneri.  This seems unlikely as the plants appear fully fertile, and V. farnesiana is usually a tetraploid (2n = 52), whereas V. schaffneri is a diploid (2n = 26).  Also, this species occurs in many areas where V. schaffneri is absent or uncommon.  Janzen and Liesner (1980) recognized the distinctness of this taxon, citing the type collection, and suggesting that it was most closely related to V. farnesiana.  Clarke et al. (1989) recognized these differences, as well as the similarity of this taxon to V. farnesiana, making it a variety of that species.  The unique morphological characteristics of this taxon, as well as its distribution support recognition as a separate species.

Clarke et al. (1989) reported that most specimens of this species were at least weakly cyanogenic, but the cyanogenic glycoside was not identified.  More recently, the authors have found many individuals of this species in Nicaragua that are not cyanogenic ever after the addition of emulsin.

Flowering time

Intermittently throughout the year.

Representative specimens






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