Acacia hindsii x A. pennatula

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 : 137

Acacia hindsii x A. pennatula .

Acacia x standleyi Saff ., J. Wash. Acad. Sei. 4: 367. 1914. Myrmecodendron standleyi (Saff.) Britton & Rose , N. Amer. FI. 23: 92. 1928. TYPE: Mexico. Nayarit: along the river in the vicinity of Acaponeta, Territory of Tepic, W Mexico, 11 Apr. 1910, J. N. Rose, P. C. Standley & P. G. Russell 14374 (holotype, US; photo, F).

Acacia x hirtipes Saff. , J. Wash. Acad. Sei. 4: 367. 1914. Myrmecodendron hirtipes (Saff.) Britton & Rose , N. Amer. FI. 23: 92. 1918. TYPE: Guatemala. Santa Rosa: along the Río de las Cañas, 3000 ft., Apr. 1892, Heyde & Lux 3299b (holotype, US; photo, NY).

Myrmecodendron oaxacanum Britton & Rose , N. Amer. FI. 23: 92. 1928. TYPE: Mexico. Oaxaca: Fonameca, 110 m, 3 July 1925, E. Makrinius 488 (holotype, US).

Shrub or small tree to 10 m tall; twigs reddish brown, glabrous to lightly puberulent. Enlarged stipular spines shiny, light gray to black, glabrous to lightly puberulent, terete to oval in cross section, the base usually flattened, symmetrical, straight, V-shaped with an angle of 80-180°, to 40 mm long, 3-7 mm wide near the base, some of the spines not enlarged, puberulent at least at the base, less than 5 mm long. Leaves 90-150 mm long; pinnae 16-31 pairs per leaf, 20-46 mm long, 4-7 mm between pinna pairs; rachis puberulent, a columnar gland with a depressed apex located near the node between each pinna pair (rarely some absent); petiole grooved, puberulent, 6-11 mm long. Petiole glands solitary, columnar to elongated, the apex depressed, puberulent, apex 1-2 mm across. Leaflets 26-40 pairs per pinna, glabrous to lightly puberulent, ciliate, linear, 2.4-3.8 (rarely 5.0) mm long, 0.7-1.1 mm wide, one vein from the base, lateral veins not obvious. Inflorescence a densely flowered cylindrical spike, 13-20 mm long, 6-8 mm thick, slightly thicker near the apex, in clusters of 1-8 in the axis of slightly reduced leaves; peduncle densely puberulent, 10-27 mm long; involucre located near the middle of the peduncle, puberulent, usually 4-lobed. Floral bracts spatulate. Corolla yellowish to reddish, about twice as long as the yellowish calyx. Fruit straight, elliptical in cross section, 40-100 mm long, 8-12 mm wide, glabrous, not striate, black to dark brown, dehiscent along one suture, short stalked, base broadly cuneate, apex narrowing to a short beak.

Representative specimens. GUATEMALA. Escuintla: in pasture above Palin , 1500 m, Standley 60100 ( F) . Guatemala: 19 km S of Guatemala City on C. A. 8 , Janzen 764 ( EIU, ILL) . HONDURAS. Comayagua: tree in dry gulch near San Luis , close to the river , Hazlett 1445 ( MO) . MEXICO. Chiapas: a unos 3 km de Ocosingo, por la orilla de la carretera que va a Tonina , Shapiro & Elliott 471 ( MICH, MO); 3.9 mi. NE of Arriaga , Janzen 758 ( EIU, ILL). Jalisco: Reserva Biosfera de la Sierra de Manantlan , 16 km by new dirt road WSW of El Terrero , Cochrane et al. 11730 ( WIS). Nayarit: 16 mi. E of San Bias , Johnson 109-73 ( MO). Oaxaca: Nejapa, a 5 km al S-SW de Santa Maria Zacatepec , Sousa et al. 10587 ( MEX); 46.7 mi. W of Tehuantepec, along hwy. 190 , Janzen 748 ( EIU, ILL) .

The densely puberulent stipular spines, petioles, rachises, peduncles, and bracts are similar to those found in A. pennatula . Also, the spatulate floral bracts are typical of A. pennatula , as are the columnar petiolar glands with a depressed apex. These hybrid specimens also have numerous characteristics of A. hindsii . The presence of enlarged stipular spines, Beltian bodies on the lower 1-2 leaflets of most pinnae, the well-developed rachis glands, and the elongated spikelike inflorescence all indicate a relationship to A. hindsii . Considering the distribution of this hybrid, the only other possible ant-acacia parent is A. collinsii . The lack of obvious secondary veins in the leaflets, the presence of rachis glands, and the small size of the leaflets, however, indicate that A. collinsii is not the ant-acacia parent. Of the specimens of this hybrid tested for cyanide production, four gave a weak to moderate positive reaction.