Acacia collinsii 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 : 135-136

Acacia collinsii x A. pennatula . Shrub or small tree to 5 m tall; twigs reddish brown, glabrous to lightly puberulent. Enlarged stipular spines shiny, dark brown to black, glabrous to lightly puberulent, terete in cross section, usually abruptly narrowing at the base, symmetrical, straight, V-shaped with an angle of 80-160°, to 40 mm long, 3-5.5 mm wide near the base, some of the spines not enlarged, puberulent at least near the base, less than 6 mm long. Leaves 80-160 mm long; pinnae 13-30 pairs per leaf, 25-45 mm long, 5-9 mm between pinna pairs; rachis lightly puberulent, rachis glands absent; petiole grooved, puberulent, 8-10 mm long. Petiolar glands 2-4, scattered along the petiole, broadly dome-shaped, the apex depressed, puberulent, striate, apex 1.4-2.5 mm across, sometimes the glands overlapping and continuous to 4.5 mm long. Leaflets 23-32 pairs per pinna, usually glabrous, linear, 4.5-5.5 mm long, 0.9-1.2 mm wide, one vein from the base, lateral veins sometimes obvious. Inflorescence a densely flowered cylindrical spike, 10-14 mm long, 6-7 mm wide, in clusters of 2-6 in the axil of slightly reduced leaves; peduncles densely puberulent, to 35 mm long; involucre usually located just below the spike, puberulent, usually 4-lobed, Floral bracts spatulate to nearly peltate with a circular apex. Corolla yellowish, about Yz as long as the calyx. Fruit straight, elliptical in cross section, to 80 mm long, 13-16 mm wide, glabrous, not striate, dark brown, probably dehiscing along one suture, short-stalked, base broadly cuneate, apex narrowing to a short beak.

Representative specimens. GUATEMALA. Guatemala: 16.2 mi. NE of Guatemala City on rd. to Puerto Barrios , Janzen 744 ( EIU, ILL). MEXICO. Chiapas: El Chorreadero, 5.6 mi. E of Chiapa de Corzo along Mexican hwy. 190 , 2500 ft., Breedlove 9638 ( F, US) ; 8.5 mi. S of La Trinitaria on hwy. 190, Janzen 571 ( EIU, ILL) . Oaxaca: 50 mi. E of Tehuantepec on hwy. 190, Seigler & Holstein 9782 ( ILL) . NICARAGUA. Estelí: 15.8 mi. W of Sebaco, 550 m, Janzen 742 ( EIU, ILL) .

The puberulent stipular spines, petioles, rachises, peduncles, and bracts of these hybrids strongly suggest that A. pennatula is the non-ant-acacia parent. Also, the young leaves are densely yellowish puberulent, a characteristic of young leaves of A. pennatula . The cylindrical spikes, the enlarged stipular spines, the presence of Beltian bodies on the lower 1-2 leaflets of most pinna pairs, the broadly dome-shaped petiolar glands, and the absence of rachis glands on the hybrid specimens indicate A. collinsii as the most probable ant-acacia parent.