Acacia sphaerocephala Schltdl. & Cham.

David S. Seigler & John E. Ebinger, 1995, Taxonomic Revision of the Ant-Acacias (Fabaceae, Mimosoideae, Acacia, Series Gummiferae) of the New World, Annals of the Missouri Botanical Garden 82, pp. 117-138 : 133-134

13. Acacia sphaerocephala Schltdl. & Cham. , Linnaea 5: 594. 1830. TYPE: Mexico. Veracruz: Actopan, sea level, Mar. 1829, Schiede & Deppe 684 (holotype, HAL, fragment and photo, F, US) .

Acacia veracruzensis Schenck , Repert. Spec. Nov. Regni Veg. 12: 362. 1913. TYPE: Mexico. Veracruz: sand dunes S of Veracruz , sea level, 13 Oct. 1908, culta in hort. bot. Darmstadt., H. Schenck 916 (lectotype, designated here, M, fragment and photo, US [B destroyed]; isotypes, F, HAL) .

Acacia dolichocephala Saff ., J. Wash. Acad. Sei. 5: 355. 1915. TYPE: Mexico. Veracruz: along the shore N of the city of Veracruz , 24 Jan. 1906, J. M. Greenman 87 (holotype, F; isotypes, GH, NY, US, photo, K) .

Small, spreading, much-branched shrub to 2 (rarely 5) m tall; young twigs dark gray to reddish brown, glabrous to lightly puberulent. Stipular spines ivory to yellow or rarely reddish to dark brown, glabrous to lightly puberulent, smooth, terete, mostly symmetrical, V-shaped, straight to slightly reflexed, 20-80 mm long, 6-16 mm thick near the base. Leaves 40-140 mm long; pinnae 5-15 pairs per leaf, 20-55 mm long, 7-17 mm between pinna pairs; rachis grooved on the upper surface, glabrous to lightly puberulent, rarely a few glands present; petiole grooved, glabrous to lightly puberulent, 6-13 mm long. Petiolar glands canoe-shaped, solitary, glabrous, striate on the sides, apex 1.4-4.5 mm long, located near the middle of the petiole, sometimes a small tubular gland below. Leaflets 16-48 pairs per pinna, glabrous, oblong, 4-10 mm long, 1.4-2.2 mm wide, lateral veins not obvious, apex mucronate. Inflorescence a densely flowered, subglobose spike less than 2 x longer than wide, 7-14 mm long, 5-7 mm wide, apex blunt, solitary or in clusters of 2-6 in the axil of small spines on short, usually leafless, axillary branches; peduncles glabrous to lightly puberulent, 7-18 mm long, 0.8-1.1 mm thick, nearly the same thickness throughout; involucre located at the base of the peduncle, glabrous to lightly puberulent, 4-lobed. Floral bracts peltate, apex circular, the stalk 0.9-1.5 mm long. Flowers sessile; calyx 5-lobed, glabrous to lightly puberulent, 1-1.5 mm long; corolla 5-lobed, glabrous, pale yellow, 1.2-1.8 mm long, only slightly longer than the calyx. Legumes straight, nearly terete, 30-80 mm long, 12-15 mm thick, glabrous, longitudinally striate, red to maroon, in- dehiscent, stipe to 10 mm long, the apex narrowing to a spinelike beak 10-30 mm long. Flowering December-April.

Distribution. Native on sand dunes and in dry places near the coast in Tamaulipas, San Luis Po- tosi, and Veracruz. Naturalized elsewhere in southern Mexico.

Representative specimens. MEXICO. Colima: 2 km S of Rancho Blanca , litis et al. 681 ( WIS) . Michoacan: a 2 km al NE de El Ranchito , 100 m, Soto N. et al. 2794 ( MEX) . Oaxaca: 13 mi. E of Pinotepa Nacional on Mexican hwy. 200 , Hansen et al. 1531 ( WIS) . San Luis Potosí: 10.3 mi. NE of Ciudad Valles on hwy. 110 , Janzen 1923 ( F) . Tamaulipas: vicinity of Tampico , 15 m, Palmer 133 ( F, MO, NY, US) . Veracruz: 5.1 mi. SE of Jalapa on hwy. 140 , Janzen 1921 ( F, MEX, NY) .

It is very possible that Acacia sphaerocephala represents a dry-land derivative of the widespread A. cornigera ( Janzen, 1974). These two taxa are closely related, and with sterile material the only reliable diagnostic characteristic is the lack of secondary venation in the leaflets of A. sphaerocephala . With fertile material, the subglobose inflorescence less than 2 x longer than wide, the circular apex of the peltate floral bracts, and the longitudinally striate legumes separate this species from A. cornigera .

Native populations of Acacia sphaerocephala are restricted to a relatively small area along the east coast of Mexico from the southern part of the state of Tamaulipas to just south of the city of Veracruz. Naturalized populations, probably resulting from seed dispersal by cattle and humans, have also been found in Colima, Michoacán, Morelos, and Oaxaca, and will undoubtedly be found elsewhere in Mexico where there is suitable habitat.

Janzen (1974) suggested that this species can be divided into a beach ecotype and an inland ecotype. The beach ecotype occurs on new dunes in the vicinity of the city of Veracruz, and the inland one throughout the remainder of the range of this species. The beach ecotype commonly forms dense stands of flat-topped shrubs mostly less than 1.5 m tall; the spines usually are not occupied by obligate acacia-ants, and the leaflets usually lack Beltian bodies. The inland ecotype, in contrast, occurs as scattered individuals that may reach 5 m in height; its spines are commonly inhabited by obligate acacia-ants, and its leaves produce numerous small Beltian bodies. These inland plants are morphologically very similar to A. cornigera , but usually grow on slightly drier sites. All specimens of both the inland and the beach ecotypes tested negative for cyanide production, as did fresh material of a population of 10 plants from the coastal dunes, just south of Veracruz ( Seigler & Ebinger, 1987). During the present study, all beach populations of this species examined contained numerous acacia-ants.