Acacia cookii Safford

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 : 124-125

4. Acacia cookii Safford , Science N. S. 31: 677. 1910. Myrmecodendron cookii (Saff.) Britton & Rose , N. Amer. FI. 23: 93. 1928. TYPE: Guatemala. Alta Verapaz: Finca Trece Aguas, near Secanguim , 300 m, 8 Mar. 1907, G. P. Goll 102 (holotype, US) .

Acacia bucerophora B. L. Rob ., Proc. Amer. Acad. Arts 49: 502. 1913. type: Belize. Belize: about Toledo, 4 mi. from the coast and 5 mi. from Punta Gorda , sea level, 29 Mar. 1907, M. E. Peck 632 (holotype, GH; fragment and photo, F, US; isotype, F, K) .

Tree to 12 m tall, young twigs dark reddish brown to black, densely puberulent. Stipular spines dark brown to black, smooth, terete, densely puberulent, asymmetrical, U-shaped with an angle of 25-50°, usually curved around the stem, 60-100 mm long, 3.5-5.5 mm thick near the base. Leaves 275-500 mm long, pinnae 18-40 pairs per leaf, 10-15 mm between pinna pairs; rachis grooved, densely puberulent; a depressed, elongated gland 1-3 mm long present between each pinna pair; petiole grooved, densely puberulent, 9-16 mm long. Petiolar glands elongate, located in the groove of the petiole, lower than the top of the groove and nearly the same length as the petiole, not striate, glabrous to lightly puberulent, apex 6-13 mm long. Leaflets 50-70 pairs per pinna, glabrous, linear, 6-8 mm long, 0.9-1.2 mm wide, lateral veins not obvious, only one vein from the base, apex acute. Inflorescences of densely flowered globose heads 6-8 mm across, in axillary clusters of 20-70 subtended by normal to slightly reduced leaves; peduncles glabrous to lightly puberulent, 15-30 mm long, 0.8-1 mm thick, slightly thicker near the apex; involucre located near the middle of the peduncle, 4- to 7-lobed, the lobes unequal in length. Floral bracts peltate, apex circular, stalk 0.8-1.1 mm long. Flowers sessile; calyx 5-lobed, glabrous, 1-1.3 mm long; corolla 5-lobed, glabrous, pale yellow, 1.5-1.8 mm long, about 1/3 longer than the calyx. Legumes slightly curved, flattened, 250-300 mm long, 10-16 mm wide, glabrous to lightly puberulent, not striate, dark brown to black, dehiscent along both sutures, stipe 10-40 mm long, the apex narrowing to a terminal point 10-30 mm long. Flowering November-April.

Distribution. In naturally disturbed sites along rivers and in wet forests with a very mild dry season, sea level to 400 m elevation, in Belize and Guatemala.

Representative specimens. BELIZE. Big Rock, Toledo , 200 ft., Schipp 1072 ( F, GH, MICH, MO, NY, UC) . GUATEMALA. Alla Verapaz: near the Finca Sepacuite, road from Secanguim to Sepacuite , Cook & Griggs 374 ( US) . Izabal: 2.8 mi. W of Puerto Matias de Galvez on road to Escobas , Janzen 1524 ( F, GH, MEX, MICH, MO, NY, UC) .

Acacia cookii is separated easily from other ant-acacias by its usually asymmetrical, thin, densely puberulent stipular spines that are curved around the stem. The one other species with similar spines, A. janzenii , is probably its nearest relative. Though similar, plants of these two species are easily separated. The stipular spines of A. cookii are relatively long (60-100 mm), fairly thin (3.5-5.5 mm), and densely puberulent with short gray hairs. Acacia janzenii , in contrast, has shorter (30-60 mm), relatively broad (6-9 mm) stipular spines that are densely pubescent with straight, yellowish hairs to 0.5 mm long. In A. cookii , the puberulent petioles are 9-16 mm long with a gland to 13 mm long, while in A. janzenii the pubescent petioles are less than 8 mm long and lack a gland. The rachis glands that are located between each pair of pinnae also differ in these two species, being elongate (1-3 mm) in A. cookii and much smaller (0.5-0.7 mm) and circular in A. janzenii . Further, the leaflets of A. cookii are 6-8 mm long, usually more than 1 mm wide, and have glabrous margins, while in A. janzenii they are shorter (3-5.5 mm), narrower (0.6-0.9 mm), and have ciliate margins. The arrangements of the inflorescences also differ. In A. cookii the inflorescences are in axillary clusters of 20-70 on typical branches and are subtended by normal to slightly reduced leaves. In A. janzenii some of the inflorescences are on thin fertile branchlets to 250 mm long, with 16-42 inflorescences in each of 6-12 fascicles that are usually not subtended by leaves ( Ebinger & Seigler, 1987).

Originally Acacia cookii was probably a wet forest species and was commonly found in naturally disturbed sites along rivers in very wet forests ( Janzen, 1974). Presently, it is also found along roadsides, in areas of recent landslides, and occasionally in pastures and other sites after human disturbance. According to Janzen (1974), however, this species generally disappears after a forest is cut. Like those of most wet forest ant-acacias, specimens of A. cookii generally have relatively low Beltian body production. Commonly only the lower 6-12 pairs of leaflets on a pinna produce Beltian bodies, but usually the bodies are 1-2 mm long. As in most ant-acacias, none of the specimens of this species tested positive for cyanide production.