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5. Acacia cornigera (L.) Willdenow, Sp. PI. 4: 1080. 1806. Mimosa cornigera L. Sp. PI. 520. 1753. Tauroceras cornigerum (L.) Britton & Rose, N. Amer. FI. 23: 86. 1928. TYPE: in the Linnean Herbarium, from a cultivated plant grown in the garden of George Clifford, between Haarlem and Leyden , Holland , collected by Linnaeus (No. 4) and bearing his label " Mimosa cornigera ," presumably grown from Mexican seed (Rudd, 1964) ( holotype , BM ; fragment and photo, US ) .

Acacia cornigera (L.) Willd. var. americana DC. Prodr. 2: 460. 1825.

Acacia spadicigera Schltdl. & Cham. , Linnaea 5: 594. 1830. Tauroceras spadicigerum (Schltdl. & Cham.) Britton & Rose, N. Amer. FI. 23: 85. 1928. TYPE: Mexico . Veracruz : near La Laguna Verde , Mar. 1828 , Schiede & Deppe685 ( lectotype , designated here, US , fragment [ B destroyed]) .

Acacia campecheana Schenck , Repert. Spec. Nov. Regni Veg. 12: 361. 1913. type: Mexico . Campeche : von Chrismar ( holotype , B destroyed) .

Acacia cubensis Schenck , Repert. Spec. Nov. Regni Veg. 12: 360. 1913. type: Cuba . N coast , 21 Apr. 1863 , C. Wright2402 ( lectotype , designated here, US fragment and photo [ B destroyed]; isotypes, G , GOET , HAL , JE , K , MO , US ). A note on the herbarium sheet (JE) indicates that the seeds he grew came from Martinique .

Acacia interjecta Schenck , Repert. Spec. Nov. Regni Veg. 12: 361. 1913. TYPE: Engler3870a ( lectotype , designated here, JE [ B destroyed]). Material growing in the Singapore and Kew Botanical Gardens (Janzen, 1974) .

Acacia nicoyensis Schenck , Repert. Spec. Nov. Regni Veg. 12: 360. 1913. TYPE: Costa Rica . Guanacaste : shore of the Gulf of Nicoya , sea level , Feb. 1900 , A. Tonduz13538 ( lectotype , designated here, US [ B destroyed]; isotypes, BM , GH , K , NY , US ) .

Acacia rossiana Schenck , Repert. Spec. Nov. Regni Veg. 12: 361. 1913. type: Mexico . Veracruz : Santa Lucrezia, Isthmus of Tehuantepec , 8 Oct. 1906 , H. Ross918 ( lectotype , designated here, M , photo, US ) .

Acacia furcella Saff ., J. Wash. Acad. Sei. 4: 359. 1914. TYPE: Mexico . Veracruz : shore of Lake Catemaco, southern Veracruz , 1000 ft ., 26 Apr. 1894 , E. W. Nelson427 ( holotype , US ) .

Acacia hernandezii Saff ., J. Wash. Acad. Sei. 4: 358. 1914. TYPE: Mexico . San Luis Potosi : vicinity of Rascon , 19-22 July 1905 , E. Palmer699 ( holotype , US ; isotypes, F , GH , MO , NY ) .

Acacia turgida Saff . in W. M. Wheeler, Bull. Mus. Comp. Zoology Harvard Coll. 90: plate 45, 1942 ( holotype , plate 45 in Wheeler, 1942) .

Shrub or small tree to 10 (rarely 15) m tall, young twigs dark gray to reddish brown, lightly to densely puberulent. Stipular spines light to dark brown to sometimes ivory to yellow, glabrous to densely puberulent, smooth, terete to slightly flattened, symmetrical, commonly V-shaped with an angle of 60-150°, straight to slightly reflexed near the apex, 30-100 mm long, 4-10 mm thick near the base. Leaves 40-160 mm long; pinnae 3-14 pairs per leaf, 30-70 mm long, 7-17 mm between pinna pairs; rachis grooved, glabrous to densely puberulent, rachis glands usually absent; petiole grooved, usually puberulent, 5-20 mm long. Petiolar gland (Fig. 1 F ) canoe-shaped, usually solitary, glabrous, striate on the sides, apex 1-4 mm long, located near the middle to top of the petiole, sometimes a small tubular gland below. Leaflets 15-40 pairs per pinna, glabrous, oblong, 4-11 mm long, 1.3-2.7 mm wide, 2-3 veins from the base, lateral veins obvious, apex usually mucronate. Inflorescence a densely flowered, cylindrical spike, 20-35 mm long, 8-11 mm thick near the base and narrowing slightly toward the blunt apex, solitary in the leaf axil, or solitary or in clusters of 2-4 in the axil of small spines on short, lateral, usually leafless, axillary branches; peduncles glabrous to lightly puberulent, 5-15 mm long, 2-4 mm thick, thickest just below the inflorescence; involucre usually puberulent, 4-lobed, the lobes spreading, located near the base of the peduncle. Floral bracts peltate, the apex tailed on one side, the stalk 0.7-1.3 mm long. Flowers sessile; calyx shallowly 5-lobed, glabrous to lightly puberulent on the lobes, 1-1.4 mm long; corolla glabrous, pale yellow, 1.1-1.5 mm long, only slightly longer than the calyx. Legume usually straight, mostly terete, 50-90 mm long, 13-18 mm thick, glabrous to minutely puberulent, usually not strongly longitudinally striate, mostly red to maroon, indehiscent, stipe to 10 mm long, the apex narrowing to a spinelike beak 20-50 mm long. Flowering January-July.

Distribution. Wet to relatively dry, mostly disturbed habitats at lower elevations from southern Mexico to Costa Rica.

Representative specimens. BELIZE . Mile 42.5 on Northern Hwy., N of Maskall River , Dwyer11023 ( F ) .

COSTA RICA . Guanacaste : NW of Paloverde , Barbudal Hills , Garwood et al. 570 ( F ) . EL SALVADOR . Banks of Rio Acelhuate , SE part of San Salvador , 690 m , Carlson55 ( F ) . GUATEMALA . Alla Verapaz : near Pancajche , about 360 m , Standley70768 ( F ) . El Petén : 2 mi . E of Melchor , roadside, Croat24623 ( MO ) . Escuintla : near San Jose at sea level , Standley64241 ( F ) . Retalhuleu : 9 mi . N of Champerico , Harmon2298 ( MO ) . San Marcos : 2 mi . E of the border between Mexico ( Puente Talisman) on hwy. 2 , Janzen1045 ( F , MEX , MO ) . Suchitepéquez : S of Alotenango Farm, 7 mi . S of Tiquisate along rd. within 3 mi . of ocean , 30-50 m , Steyermark47739 ( F ) . HONDURAS . Vegas del Rio Agua , 3 km de Yoro , 1000 m , Molina R. 6807 ( F ) . MEXICO . Campeche : 30 km E of Campeche on hwy. 261 , Seigler et al.11603 ( ILL , MEX ) . Chiapas : CiudadCuauhtemoc on hwy. 190 , Janzen499 ( F , MEX ) . Guerrero : 1 mi . NW Cuajinicuilapa , Johnson740-79 ( WIS ) . Oaxaca : Capilla , N end of lake behind PresaAleman , W of Tierra Blanca , Janzen1937 ( F , MO , WIS ) . Quintana Roo : 52 mi . W of jet. of Mexico 307 & 186 on hwy. 186 , Seigler et al.11594 ( ILL , MEX ) . San Luis Potosi : Barrio de San Juan , Tamazunchale , Edwards600 ( F , MO ) . Tamaulipas : Tampico, Rujal rd. , Kenoyer791 ( F ) . Veracruz : Zacuapán , Purpas7748 ( GH , MO ) . Yucatan : Izarnal , Greenman379 ( GH ) . NICARAGUA . Laguna de Masaya , a 2 km de la entrada , Araquistain & Moreno593 ( MEX ) .

Acacia cornigera is probably the best known of the ant-acacias. It is easily separated from other ant-acacias by having peltate floral bracts in which the apex is tailed on one side. Also, the presence of canoe-shaped petiolar glands separates this taxon from all ant-acacias except A. mayana and A. sphaerocephala . The presence of obvious secondary venation in the leaflets and the relatively thick cylindrical inflorescences separate this taxon from A. sphaerocephala , while the smaller leaflets and the lack of longitudinal flanges on the stipular spines separate it from A. mayana .

Acacia cornigera is a highly variable species that occurs in a wide range of habitats. This morphological diversity has resulted in an extensive synonymy, which is discussed by Rudd (1964). It is the most common of the ant-acacias, and its geographic range is almost as extensive as that of A. collinsii . It is relatively common in riparian and swamp habitats and is the common ant-acacia in fallow fields, pastures, roadsides, and other disturbed sites from sea level to about 1200 m (Janzen, 1967a, b). Some of its present distribution has been caused by the dissemination of seeds by birds, people, and cattle into secondary growth vegetation. The present distribution of this species into the drier parts of the Yucatan peninsula is probably due to introduction by humans, since most collections are from around settlements, cattle corrals, and Indian ruins. It has also become naturalized on the Caribbean islands of Martinique , Guadeloupe , andCuba , as well as in extreme southern Florida.

Beltian body production in Acacia cornigera is typical of that found in ant-acacias that inhabit more open sites. Generally, these bodies are relatively small, 0.5-0.9 mm long, 0.4-0.6 mm wide, and are present on more than half of the leaflets. Since individuals of this species are usually occupied by obligate acacia-ants, the Beltian bodies are rarely seen because they are usually “harvested” as soon as the young leaves develop.

Of the more than 250 herbarium specimens of this species examined, none tested positive for cyanide production. Also, numerous living specimens have been tested, usually with negative results. Leaves of Acacia cornigera have been reported to contain a ß-glucosidase (Rehr et al., 1973). It appears that the hydrolytic enzyme necessary for the liberation of HCN is present, but the cyanogenic glycoside is absent. Living material from two populations of this species collected near Canas, Guanacaste Province, Costa Rica, gave a very weak positive test for cyanide (Seigler & Ebinger, 1987). Dried material from these same individuals gave a negative test with and without emulsin.

Janzen (1974) reported seeing a single plant of A. cornigera x A. sphaerocephala on the dunes south of Veracruz, Mexico, and suggested that A. cornigera may occasionally hybridize with A. chiapensis . It is also possible that this species may occasionally hybridize with the non-ant-acacia A. pennatula (Ebinger & Seigler, 1992).

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