Vachellia pennatula

Vachellia pennatula

Vachellia pennatula

Vachellia pennatula var. pennatula - leaf

Vachellia pennatula var. pennatula - leaves gland

Vachellia pennatula var. pennatula - flowers

Vachellia pennatula var. pennatula - gland

Vachellia pennatula var. pennatula - spines


Vachellia pennatula (Schlechtendal & Chamisso) Seigler & Ebinger var. pennatula,  Phytologia 87:164. 2005
Syn.  Acacia pennatula (Schltdl. & Cham.) Benth., London J. Bot. 1:390. 1842.

Synonymy and types

Basionym:  Inga pennatula Schltdl. & Cham., Linnaea 5:593. 1830. - Acacia pennatula (Schltdl. & Cham.) Benth., London J. Bot. 1:390. 1842. - Poponax pennatula (Schltdl. & Cham.) Britton & Rose, N. Amer. Fl. 23:88. 1928. - TYPE: MEXICO. VERACRUZ: municipio de Xico, region of Jalapa, Hacienda de la Laguna, Aug. 1828, C.Schiede & F.Deppe s.n. (holotype: HAL). NOTE: The type material is a mixture from Jalapa and from near Hacienda de la Laguna. Schlechtendal and Chamisso (1830) mention both in the original description and both are Vachellia pennatula.

Acacia lanata M. Martens & Galeotti, Bull. Acad. Roy. Sci. Bruxelles 10:315. 1843. - TYPE: MEXICO. OIAXACA: Misteca Alta, Apr. 1840, a 7-8,000 pieds, H.Galeotti 3231 (holotype: BR; isotypes: P, G). (Rudd 1976-1982)

Pithecollobium minutissimum M. E. Jones, Contr. W. Bot. 18:38. 1933. - TYPE: MEXICO. JALISCO: Guadalajara, La Barranca, 25 Nov. 1930, M.E.Jones 27266a (holotype: RSA-POM).

Formal description

Tree to 15 m tall. Bark dark brown to dark gray, smooth to shallowly furrowed. Twigs dark reddish brown to dark gray, slightly flexuous, densely pubescent with erect, yellow-green hairs mostly more than 0.3 mm long. Short shoots absent. Leaves alternate, 60-200 mm long. Stipular spines reddish brown, symmetrical, terete, straight, stout, to 25(40) x 1-3 mm near the base, densely pubescent at the base and sometimes throughout with erect, yellow-green hairs. Petiole adaxially grooved, 3-8 mm long, densely pubescent; petiolar gland solitary, located on the upper half of the petiole, sessile, circular to slightly elongated, 1.0-2.5 mm long, apex flattened with the margins sometimes raised, glabrous. Rachis adaxially grooved, 60-200 mm long, densely pubescent, a sessile, circular gland, 0.4-0.7 mm across, between the upper 1 to 3(5) pinna pairs. Pinnae 17 to 48 pairs per leaf, 15-38 mm long, 2-5 mm between pinna pairs. Petiolules 0.4-1.1 mm long. Leaflets 24 to 60 pairs per pinna, opposite, 0.3-0.6 mm between leaflets, linear, 0.8-3.0 x 0.4-0.7 mm, glabrous to lightly pubescent, lateral veins not obvious, only one vein from the base, base oblique, margins ciliate, apex broadly acute to obtuse. Inflorescence a densely flowered globose head 9-16 mm across, solitary or in clusters of 2 to 5(10) in the leaf axil. Peduncles 12-30 x 0.5-0.8 mm, densely puberulent with erect, yellow-green hairs. Involucre 4- to 6-lobed, located at the base of the globose head, puberulent, persistent. Floral bracts spatulate, 1.2-2.0 mm long, apex puberulent, deciduous. Flowers sessile, yellow; calyx 5-lobed, 0.7-1.6 mm long, the lobes puberulent; corolla 5-lobed, 2.0-2.6 mm long, the lobes puberulent; stamen filaments 3.0-4.5 mm long, distinct; ovary glabrous to lightly pubescent, on a stipe to 0.2 mm long. Legume dark brown to black, straight, not inflated, flattened to slightly elliptic in cross section, not constricted between the seeds, oblong, 50-160 x 16-30 mm, coriaceous, reticulately striate, glabrous, glandular, indehiscent; stipe mostly absent; apex rounded. Seeds uniseriate, imbedded in a light brown pulp, light brown, ovoid to ellipsoid, slightly flattened, 6.5-8.4 x 4.2-6.0 mm, smooth; pleurogram U-shaped, 2-4 mm across. Flowers from March to June Mexico and Central America, and from May to December in South America.  Chromosome number: Not determined.


Disturbed relatively dry sites between 500 and 2500 m elevation throughout all but northern Mexico, south into El Salvador, Guatemala, Honduras and Nicaragua, and northern South America in southern Columbia (Valle) and Ecuador.

Additional info

Vachellia pennatula var. pennatula is a wide-ranging species throughout most of Mexico and Central America (Seigler and Ebinger 1988). In South America it has a limited distribution, occurring at a few sites in southern Columbia, and scattered localities in Ecuador. This distribution suggests that the taxon was introduced into South America, as some of the collections in Columbia are from a botanical garden, and most of the sites in Ecuador are from the vicinity of Guayaquil.  Chazaro Basanez (1977) and later Purata et al. (1999) give a detailed account of the phenology, ecology and economic importance of this species in Veracruz, Mexico.

Vachellia pennatula var. pennatula is most closely related to V. macracantha and V. cochliacantha.  All three taxa are common throughout Mexico, and occasionally occur together. Vachellia pennatula can easily be separated from these two taxa by its sessile petiolar glands, the dense, gray to yellow-green pubescence that covers most young parts of the plant, and the thicker (7-12 mm) and wider (12-30 mm) fruits. Also, V. cochliacantha has large spoon-shaped stipular spines while those of V. pennatula are smaller and terete. Of material examined from Mexico, only 21% of the specimens tested contained cyanogenic compounds (Seigler et al.1978; Seigler and Conn 1982, Seigler and Ebinger 1988), while all of the specimens tested from South America were cyanogenic, usually strongly so.

Throughout most of its geographic range this variety is very consistent in its morphological characteristics. The dense yellow-green pubescence is a very obvious on most specimens, being particularly dense on new growth. On old material, however, it is not as dense, and turns lighter in color. Also, the leaflets are usually extremely small, mostly less than 1.5 mm long, and can be used to separate this taxon from V. cochliacantha and V. macracantha.  Sometimes, however, the leaflets may reach a length of 3 mm, particularly in the material from South America.

Vachellia pennatula is closely related to V. macracantha, and in areas of sympatry hybrids are occasionally found. In a study of five disturbed pastures in the state of Veracruz, Ebinger and Seigler (1987) found plants of V. pennatula and V. macracantha along with F1 hybrids and backcrosses individuals.  Hybrids of these two taxa are rarely, if ever, found outside areas of sympatry.  This hybrid was described as the species Poponax attenuata by Britton and Rose (1928). Vachellia pennatula also hybridizes with some ant-acacias. Vachellia chiapensis, V.collinsii, V. hindsii (V. X standleyi.) and possibly V. cornigera occasionally hybridize with V. pennatula in regions of sympatry (Ebinger and Seigler 1992, Seigler and Ebinger 1995). The hybrid V. X standleyi is probably the most common hybrid involving an ant-acacia. Both putative parents are wide-ranging species in western Mexico and throughout much of Central America.

The two varieties of Vachellia pennatula (pennatula and pavicephala) are easily separated. Variety pennatula consistently has large spherical inflorescences that are 9 to 13 mm in diameter (5-8 mm in diameter for var. parvicephala), and the twigs, petioles, and peduncles are densely pubescent with spreading to erect yellow-green hairs that are mostly more than 0.3 mm long (var. parvicephala has matted white to gray hairs mostly less than 0.3 mm long).

Flowering time

March - June in Mexico and Central America, and May - December in South America.

Representative specimens








Depto Ahuacha:

Depto Metapan:

Depto Santa Ana:







El Praraiso:

Francisco Morazán:



















Quintana Roo:

San Luís Potosí:









El Bosque:









Nueva Segovia: