Vachellia pennatula (Schlechtendal & Chamisso) Seigler & Ebinger var. pavicephala (Seigler & Ebinger) Seigler & Ebinger. Phytologia 87:164. 2005. syn. Acacia pennatula (Schltdl. & Cham.) Benth. subsp. parvicephala Seigler and Ebinger, Syst. Bot. 13:12. 1988.
Synonymy and types
Basionym: Acacia pennatula (Schltdl. & Cham.) Benth. subsp. parvicephala Seigler and Ebinger, Syst. Bot. 13:12. 1988. - TYPE: MEXICO. YUCATAN: Chichén Itzá, in second growth, 6 Jun. 1938, C.L.Lundell & Lundell 7418 (holotype: F; isotypes: LL, NY, TEX, US).
Tree to 15 m tall. Bark dark brown to dark gray, smooth to shallowly furrowed. Twigs dark reddish brown to dark gray, slightly flexuous, pubescent with matted, white to grayish hairs mostly less than 0.3 mm long, sometimes becoming glabrous with age. 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, pubescent with matted, white to grayish hairs mostly less than 0.3 mm long, sometimes becoming glabrous with age; 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 5-8 mm across, solitary or in clusters of 2 to 5(10) in the leaf axil. Peduncles 7-12 mm long, densely pubescent with matted, white to grayish hairs, sometimes becoming glabrous with age. 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, 0.4-0.8 mm long, the lobes puberulent; corolla 5-lobed, 1.4-1.9 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, 50-90 x 12-16 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 May. Chromosome number: Not determined.
In arid, mostly disturbed habitats from sea level to 1500 m in southern Mexico, and south into Honduras.
Vachellia pennatula var. parvicephala has a very restricted geographic range in southern Mexico and Central America, and many of the collections are at relatively low elevations, some from near sea level. Flowering material is easily separated from var. pennatula as the inflorescences are much smaller (5-8 mm across), the flowers and floral bracts are smaller, and the peduncles are very short, less than 12 mm long. Mature fruiting material also differs, but overlaps in its characteristics with var. pennatula. Generally fruits of var. parvicephala are smaller than those of var. pennatula, being less than 90 mm long, less than 16 mm wide, and 6-10 mm thick. Vachellia pennatula var. pennatula fruits, in contract, are usually longer, mostly 16-30 mm wide, and 7-12 mm thick. Sterile material is more difficult to distinguish as the thick yellow-green pubescence of var. pennatula become less obvious and thinner in older material.
More than 40 specimens of Vachellia pennatula var. parvicephala were tested for the presence cyanide and more than 50% gave a positive reaction (Seigler and Ebinger 1988). The cyanogenic glycoside present is proacacipetalin, the same compound found in V. macracantha.
Based on the description given by Standley (1930a, 1930b), it is probable that he intended his name Acacia milleriana to apply to this small inflorescence form of A. pennatula. Standley, however, based his name on Mimosa campechiana Miller (1768), which is a synonym of A. cochliacantha (Rudd 1966). The valid name for this taxon therefore is var. parvicephala.
March - May.
- Valle de El Espino cerca de San Jerónimo, alt. 350 m, 14 Apr 1957, A.Molina R. 8062 (MO);
- Jardín del Loarque, alt. 950 m, 30 Mar 1983, D.R.Bados S. 161 (ILL, MO);
- Tegucigalpa, colonia Lomas del Guijarro, alt. 950 m, 4 Apr 1982, L.R.de Belibasis 177 (ILL, MO);
- comayaguela D.C., alt. 1000 m, 21 Oct 1983, C.Bendeck E. 88 (ILL, MO);
- Tegucigalpa, Ciudad Universitaria, alt. 950 m, 22 Apr 1983, S.C.Cerna 139 (ILL, MO);
- Campo Universidad Nacional Autónoma de Honduras, carretera Suyapa, alt. 2000 m, 21 Nov 1979, C.A.Cerrato B. 121 (ILL, MO);
- Campo Universidad Nacional Autónoma de Honduras, carretera aldea Suyapa, alt. 1000 m, 13 Mar 1980, C.A.Cerrato B. 167 (ILL, MO);
- Valle de Siria, alt. 700 m, 7 May 1978, T.Clare 66 (MO);
- Tegucigalpa, campos abiertos, alt. 950 m, 22 Apr 1983, M.A.Echeverria 162 (ILL, MO);
- El Hatillo, 15 km NE de Tegucigalpa, alt. 1500 m, 3 May 1983, C.Garcés 200 (ILL, MO);
- Valley of Los Limones, 7 km S of Moroceli, alt. 700 m, 18 Mar 1982, C.E.Hughes & B.T.Styles 110 (MO);
- Tegucigalpa, alt. 1200 m, 5 Mar 1980, E.Joya 138 (ILL, MO);
- Valle de Angeles, 20 km NE de Tegucigalpa, alt. 1400 m, 28 May 1982, L.Marineros 217 (ILL);
- alrededores de Mateo, 12 km SW de Tegucigalpa, alt. 950 m, 1 May 1984, R.M.Rivas 166 (MO);
- Tegucigalpa, alt. 950 m, 29 Apr 1984, G.Soihet 156 (ILL, MO);
- Tegucigalpa, carretera a Valle de Angeles, alt. 1000 m, 30 Apr 1982, C.M.Torres F. 139 (ILL);
- along Río de la Orilla near Cerro Majicarán, alt. 800 m, 18 Apr 1948, L.O.Williams 14069 (MO);
- Victoria, alt. 339, 21-23 Jan 1981, C.Nelson 7101 (ILL);
- 4 km al S de Constitución, 10 Jul 1983, E.Cabrera & O.Canul 5057 (MO);
- Bolonchen de Rejón, orilla S del Pueblo, alt. 120 m, 18 May 1982, M.Sousa, E.Cabrera, G.Davidse & A.Chater 12431 (ILL, MO);
- above the settlement of Toliman, 38 km W of Huixtla on the road to Motozintla, alt. 1250 m, 30 Jun 1972, D.E.Breedlove 25937 (MO);
- 5 km N of Cintalapa, alt 800 m, 25 Aug 1974, D.E.Breedlove 3660 (MO);
- 6 km al E de Amatenango del Valle, alt. 5100 ft. 17 Apr 1988, M.Gómez L. 424 (TEX);
- 7 miles W of Tuxtla Gutierrez, 17 Jun 1968, C.D.Johnson 136-68 (MO);
- 2 miles NW of Comitan, alt. 5900 ft., 31 Mar 1979, C.D.Johnson 1045-79 (MO);
- about 20 km E of Tuxtla Guttíérrez, alt. 3500 ft., 17 Apr 1945, E.L.Little, Jr. & A.J.Sharp 9815 (TEX);
- 10 km S of Ciudad de Las Casas, alt. 6000 ft., 24 Apr 1945, E.L.Little, Jr. & A.J.Sharp 9977 (TEX);
- 5 km al E de La Cabecera de Amatenango, alt. 5500 ft. 9 Mar 1988, J.López P. 413 (TEX);
- Siltepec, 8 Aug 1937, E.Matuda 1585 (LL, MICH);
- La Grandeza, alt. 2016 m, 19 May 1945, E.Matuda 5544 (LL);
- 1 km al S de Finca San Julián, alt. 600 m, 12 Nov 1989, A.Reyes G. 1405 (TEX);
- 5.6 miles SE of Chiapa de Corzo, 28 Nov 1967, A.S.Ton 3289 (LL);
- en el cerro camino Tzajal ja, alt. 1700 m, 18 May 1982, A.S.Ton 4295 (MO);
- Santa Cruz en San Filipe, 15 Nov 1986, M.M.Ton 9819 (MICH, TEX);
- en los alrededores de la Laguna Muyil, a 20 km al S de Tulum, 7 Aug 1982, E.Cabrera & H.de Cabrera 3382 (MO);
- en el Rancho el Ramonal, 11 Jun 1983, R.Durán, I.Olmsted O.Barrera 200 (MO);
- Laguna Mujil, a 1 km al E de las Ruinas de Chunyaxche, 19 May 1982, M.Sousa, E.Cabrera, G.Davidse & A.Chater 12446 (MO);
- Afueras de Akumal, 6 Apr 1980, O.Téllez & E.Cabrera 1912 (MO);
- en Ruinas de Coba, 6 Jun 1980, O.Téllez & E.Cabrera 2358 (MO);
- X-Conha, Felipe Carrillo Puerto, alt. 16 m, 26 May 1985, E.Ucan 4058 (MO);
- W of Ticul, 9 Nov 1979, A.S.Bradburn 1403 (MO);
- 3 km W Valladolid, 24 Dec 1978, R.Conway & C.D.Johnson 444-78 (ILL, MO);
- Oxkintok, between Opichen and Maxcanu, 31 Dec 1981, S.Darwin & E.Sundell 2070 (MO);
- NNE de Temax, 14 Oct 1956, Enriquez 555 (US);
- Chichankanab, no date, G.F.Gaumer 1370 (F, MO);
- Kancabonot, May 1917, G.F.Gaumer 23871 (F, MO);
- 1917-1921, G.F.Gaumer 23947 (MO);
- Itzimne, 19 Feb 1906, Greenman 334 (F, NY);
- Chichén Itzá, 6 Jun 1938, C.L.Lundell & A.A.Lundell 7418 (TEX);