Acacia hindsii Benth

8. Acacia hindsii Benth., London J. Bot. 1: 504. 1842. Myrmecodendron hindsii (Benth.) Britton & Rose, N. Amer. FI. 23: 91. 1928. TYPE: Mexico. Jalisco: shore of Manzanilla Bay, sea level, 1841, R. B. Hinds 248 (holotype, K, photo, F).

Acacia bursaria Schenck, Repert. Spec. Nov. Regni Veg. 12: 363. 1913. TYPE: Guatemala. Amatitlán: Laguna Amatitlán, 3900 ft., Feb. 1890, J. D. Smith 2304 (lectotype, designated here, US [B destroyed]; isotypes, GH, K).

Acacia tepicana Saff., J. Wash. Acad. Sei. 4: 366. 1914. TYPE: Mexico. Nayarit: thickets, vicinity of Acaponeta, Tepic, 30 m, 10 Apr. 1910, J. N. Rose, P. C. Standley & P. G. Russell 14357 (holotype, US, photo, F; isotype, NY).

Acacia sinaloensis Saff., J. Wash. Acad. Sei. 4: 365. 1914. TYPE: Mexico. Sinaloa: vicinity of Villa Union, growing about a pond, 2 Apr. 1910, J. N. Rose, P. C. Standley & P. G. Russell 13972 (holotype, US; isotype, NY).

Tree to 10 m tall; young twigs reddish brown to dark brown, glabrous to rarely lightly puberulent. Stipular spines (Fig. 1 C) shiny, light brown to nearly black (sometimes light gray), smooth, glabrous to lightly puberulent, flattened at the base, symmetrical, nearly flat to broadly U-shaped across the top at an angle of 90-180°, 30-55 mm long, 10-20 mm wide at the base. Leaves 45-180 mm long; pinnae 10-18 pairs per leaf, 20-45 mm long, 6-12 mm between pinna pairs; rachis grooved, usually puberulent, a small narrow volcano-shaped gland located at the node between each pinna pair; petiole grooved, usually densely puberulent, 7-14 mm long. Petiolar glands narrow volcano-shaped (to almost columnar), usually 3-7 (rarely 1) scattered along the petiole, puberulent, lightly striate, apex 0.4-0.7 mm long, base 0.8-1.2 mm long. Leaflets 12-30 pairs per pinna, glabrous, linear, 3-7 mm long, 0.9-1.4 mm wide, one vein from the base, lateral veins not obvious, apex obtuse, margins lightly ciliate. Inflorescence a loosely flowered, cylindrical spike, 20-50 mm long, 4-7 mm thick, nearly the same thickness throughout, apex blunt, in racemes with 1-3 (rarely 4-8) spikes at each node in the axil of a reduced leaf; peduncles glabrous to lightly puberulent, 10-20 mm long, 0.6-1.1 mm thick, nearly the same thickness throughout; involucre located at the base to the lower third of the peduncle, puberulent, 4-lobed with 2 lobes longer. Floral bracts peltate, apex circular, stalk 0.4-0.7 mm long. Flowers sessile; calyx 5-lobed, puberulent, 0.5-0.9 mm long; corolla 5-6-lobed, puberulent, yellowish, 1.6-2.0 mm long, usually more than twice as long as the calyx. Legumes curved, elliptical in cross section, 40-100 mm long, 8-12 mm wide, glabrous to lightly puberulent, usually not striate, black to dark brown, dehiscent along one suture, short stalked, base narrowly cuneate, the apex narrowing to a beak 10-15 mm long. Flowering January-July.

Distribution. Disturbed, usually wet sites of the Pacific lowlands and foothills from extreme southern Sinaloa, Mexico, south to Nicaragua.

Representative specimens. EL SALVADOR. La Union: vicinity of La Union, 150 m or less, Standley 20663 (NY, UC, US). San Vicente: vicinity of Apastepeque,, Standley 21333 (NY). Sonsonate: vicinity of Acajutla, 30 m or less, Standley 21942 (US). GUATEMALA. Alta Verapaz: near Pancajche, about 360 m, Standley 70648 (F). Escuintla: S of Rio Burrion, NE of Escuintla, about 700 m, Standley 89619 (F). Retalhuleu: vicinity of Retalhuleu, 240 m, Standley 88846 (F). San Marcos: Sands, Ocos, 1-2 m, Steyermark 37779 (F). HONDURAS. Encinales del Valle de El Espino cerca de San Jeronimo, 350 m, Molina R. 8059 (F, MO, US). MEXICO. Chiapas: 13 mi. NE of the border of Chiapas & Oaxaca on hwy. 190, Seigler et al. 11583 (ILL). Colima: Manzanillo, Palmer 1395 (MO, NY, US). Guerrero: sandy river bank, Tecpan- El Verde, 20 m, Hinton 14120 (MO, TEX, US). Jalisco: just E of Barra de Navidad in sandy soil near sea level, in thickets about margin of palm forest, McVaugh 11847 (US). Michoacán: a 10 km aprox. al N de-Playa Azul, carr. a Nueva Italia, Nunez & Boom 2115 (MO). Nayarit: 4 mi. S of intersection to Acaponeta on hwy. 15, Seigler et al. 11797 (ILL). Oaxaca: sand dunes behind the beach at Salina Cruz, King 2461 (TEX, US). Sinaloa: near Colomas, in the foothills of the Sierra Madre, Rose 1766 (NY).

Like Acacia collinsii and A. cornigera, A. hindsii has an extensive geographical range. Unlike these species, however, A. hindsii is restricted to the Pacific lowlands and foothills in Central America. Before the existence of extensive agriculture in the region it was probably common along rivers, in semideciduous and deciduous forests, and in mangrove swamps (Janzen, 1974). Presently it is a common element of shrubby regeneration, particularly in wetter habitats such as river banks, where it commonly forms dense thickets by means of root sprouts.

Acacia hindsii is easily separated from all other ant-acacias by its stipular spines, which are flattened at the base and nearly flat to broadly U-shaped across the top. It is morphologically very similar to A. collinsii and A. gentlei, both of which have relatively small leaves and cylindrical spikes, but differs in leaflets that lack obvious secondary venation.

As is typical of most ant-acacias that inhabit more open sites, Beltian body production in Acacia hindsii is relatively extensive. In this species the small, slightly elongated Beltian bodies usually are less than 1 mm long, and are found commonly on more than 60% of the leaflets of developing leaves. As most individuals of this species are inhabited by obligate acacia-ants, the Beltian bodies generally are not seen, being “harvested” soon after development.

Acacia hindsii is polymorphic with respect to HCN production (Seigler & Ebinger, 1987), being reported acyanogenic by Rehr et al. (1973), while Seigler et al. (1978) found individuals that are strongly cyanogenic. Of more than 300 herbarium specimens tested, 123 were positive for HCN production. In general, many of the specimens from Mexico tested positive for cyanide, while most of the acyanogenic specimens are from Guatemala, El Salvador, and Honduras. The glycoside in this species is proacacipetalin.

Acacia hindsii probably hybridizes with the ant-acacia A. collinsii. It also has been reported to hybridize with non-ant-acacias of the A. macracantha complex, particularly A. pennatula (Acacia x standleyi Safford), and A. cochliacantha (Acacia x gladiata Safford).