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Vachellia x cedilloi (L. Rico) Seigler & Ebinger (fabaceae: mimosoideae), a probable hybrid of two species of ant-acacias.

The genus Vachellia, which includes species of Acacia sensu lato with paired stipular spines, consists of 60 species in the New World tropical and subtropical areas ranging from southern United States south to Argentina (Seigler and Ebinger, 2005). Nearly 100 additional species are in the Old World tropics and subtropics of Asia, Africa, and Australia. Hybrids between New Word species of Vachellia are found occasionally. These hybrids mostly involve the Vachellia macracantha species group that includes 14 ant-acacias and eight non-ant-acacias related to V. macracantha (Humb. & Bonpl. ex Willd.) Seigler & Ebinger (Ebinger and Seigler, 1992; Seigler and Ebinger, 1995; Maslin and Stirton, 1997).

Hybrids between species of ant-acacias and between ant-acacias and non-ant-acacias have been discussed by Janzen (1974), Ebinger and Seigler (1992), and Seigler and Ebinger (1995). These studies indicated that at least four species of ant-acacias hybridize with various species of non-ant-acacias of the V. macracantha complex, including V. campechiana (Mill.) Seigler & Ebinger, V. macracantha,andV. pennatula (Schltdl. & Cham.) Seigler & Ebinger (Ebinger and Seigler, 1987; Seigler and Ebinger, 1988).

Hybrids between species of ant-acacias are not as common. Seigler and Ebinger (1995) reported one probable hybrid specimen between V. collinsii (Saff.) Seigler & Ebinger x V. hindsii (Benth.) Seigler and Ebinger. Earlier, Janzen (1974) reported hybrids involving parents of ant-acacias; V. cornigera (L.) Seigler & Ebinger x V. sphaerocephala (Schltdl. & Cham.) Seigler & Ebinger; and V. chiapensis (Saff.) Seigler and Ebinger x V. cornigera. in neither case were specimens cited, and we have been unable to locate voucher specimens. Typically, hybrid individuals involving ant-acacias are extremely rare, only one to a few individuals within any given area. These hybrids usually are associated with disturbance, commonly in pastures or at the edge of roads. The present study was undertaken to determine whether V. x cedilloi (L. Rico) Seigler & Ebinger is of hybrid origin, as indicated by the intermediacy of characters, and whether V. cornigera and V. globulifera (Saff.) Seigler & Ebinger are the probable parents.

The present treatment is based on herbarium specimens, including an isotype and two other collections of V. x cedilloi along with representative specimens of the putative parents from southern Mexico and Central America (Appendix). Initially, specimens were separated into taxonomic groups based on overall morphological similarity. These specimens were scored for nine vegetative and seven floral characters (Appendix). These data served as the source of characters for principal-component and principal-coordinate analyses. For each continuous character of each specimen, [greater than or equal to]3 measurements were made. These values were plotted to confirm that gaps existed in the data.

A principal-component analysis to identify groupings of specimens examined was conducted. For this analysis, data were first standardized and a correlation matrix, eigenvalues, and eigenvectors were calculated using NTSYS-pc verson 2.1 (Rohlf, 2000). Eigenvectors were scaled by the square root of lambda ([lambda]). Axes were rotated and resulting loadings were represented graphically as two-dimensional and three-dimensional plots (Fig.1).

For the principal-coordinate analysis, Gower's resemblance coefficients were calculated (Legendre and Legendre, 1983; Podani, 1999). The nature of each character was designated as binary, multistate, or quantitative descriptors, and all characters were weighted equally. The data matrix was transformed by the DCENTER algorithm using distances squared and eigenvectors and eigenvalues were calculated with NTSYS-pc verson 2.1 (Rohlf, 2000). Eigenvectors were scaled by the square root of lambda ([lambda]). The resulting loadings were represented graphically as two-dimensional and three-dimensional plots (Fig. 1).

Results of principal-component analysis based on all 16 characters and a principal-coordinate analysis based on Gower's similarity coefficients (Fig. 1) proved to be similar. In the principal-component analysis, the first three principal components accounted for 97% of the total variance. Shape of inflorescence, thickness of peduncle, venation of leaflet, and apex of floral bract (characters 10, 12, 9, and 13) were most important for determining the component score of the first axis; shape of rachis gland and length of leaflet (characters 3 and 7) were most important for determining the second axis, whereas the most important character for determination of the third axis was symmetry of stipular spine (character 1). Species used in this analysis represented distinct groupings in both principal-component and principalcoordinate analyses. Results of analyses were used to help delineate species and prepare the description of V. x cedilloi.

Rico Arce (1994) considered V. x cedilloi to be closely related to V. globulifera, which it resembles in some of its vegetative characteristics, particularly the columnar to narrow volcano-shaped glands on the rachis between each pair of pinnae. The glands of V. x cedilloi are similar to those of V. globulifera, except that they usually are glabrous and more columnar, whereas those of V. globulifera are densely puberulent and narrow volcano-shaped. Plants of V. globulifera occur in the same part of Quintana Roo, Mexico, as those of V. x cedilloi. Other species of antacacias in Quintana Roo, V. collinsii (Safford) Seigler & Ebinger and V. gentlei (Standley) Seigler & Ebinger, are not similar morphologically to V. x cedilloi in shape of stipular spines, petiolar glands, or rachis glands.

In most respects, the probable hybrid is more similar to V. cornigera, which is also in this region. in V. x cedilloi,as in V. cornigera, the leaves have relatively few pairs of pinna (6-12). Leaflets are nearly as large as those of V. cornigera, but lack the obvious secondary veins of that species. Inflorescences and fertile branches of V. x cedilloi are exactly alike, although miniature copies, those in V. cornigera, being about one-half the size, cylindrical, and narrow toward the apex. Flowers of the probable hybrid are nearly identical and about the same size as those of V. cornigera. Inflorescences are solitary or in clusters of two in the axil of small spines on short, usually leafless axillary branches, also nearly identical to those of V. cornigera. It is likely that V. x cedilloi represents a hybrid between V. cornigera and V. globulifera.

[FIGURE 1 OMITTED]

Vachellia x cedilloi (L. Rico) Seigler & Ebinger, Phytologia 87:150 (2005).--Acacia cedilloi L. Rico, Acta Botanica Mexicana 26:7 (1994). Type: Mexico: Quintana Roo: km 6.5 de la carretera Vigia Chico-F. Carrillo Puerto, selva mediana subperennifolia, 8 m elevacion, 9 April 1986, R Villanueva 714 (holotype: MEXU; isotypes: MO, XAL). Tree to 3 m tall. Twigs pale brown to pale gray, not flexuous, glabrous. Short shoots absent. Prickles absent. Leaves alternate, 60-150 mm long. Stipular spines usually pale brown to pale reddish brown, asymmetrical and curved around the stem, terete, woody, and inflated, 20-80 by 4-10 mm near the base, glabrous, many stipular spines not enlarged, persistent. Petiole adaxially grooved, 8-18 mm long, glabrous to lightly puberulent, petiolar glands absent. Rachis adaxially grooved, 50-140 mm long, glabrous to lightly puberulent, a sessile, narrowly volcano-shaped to nearly columnar gland usually present between each pair of pinnae, apex 0.4-0.6 mm across, mostly glabrous and striate. Pinnae 6-12 pairs/leaf, 28-60 mm long, 714 mm between pairs of pinnae. Paraphyllidia absent. Petiolules 0.8-1.4 mm long. Leaflets 12-28 pairs/pinna, opposite, 1.1-2.1 mm between leaflets, linear, 4-9 by 1.5-2.5 mm, glabrous, lateral veins not obvious, 1 vein from the base, base oblique, margins not ciliate, apex usually obtuse, midvein subcentral; beltian bodies not seen, but scars are present where they were located. Inflorescence a densely flowered cylindrical spike ca. 23 times longer than wide that narrows slightly toward the blunt apex, 7-15 by 4-8 mm near the base, solitary or in clusters of two in the axil of small spines on short, usually leafless axillary branches <130 mm long with <15 nodes. Peduncles 4-7 by 1.4-2.2 mm, glabrous; receptacle slightly enlarged near the middle, involucre 5-7-lobed, located at the base to lower one-third of peduncle, persistent. Floral bracts peltate, 0.7-1.1 mm long, apex circular and glabrous, deciduous. Flowers sessile, pale yellow; calyx five-lobed, 0.9-1.3 mm long, glabrous; corolla five-lobed, 1.0-1.4 mm long, glabrous, lobes less than one-quarter length of corolla; stamen filaments 1.2-1.6 mm long, distinct; anther glands absent; ovary glabrous, sessile. Legume dark gray, slightly curved, nearly terete in cross section, not constricted between seeds, oblong, 50-100 by 10-15 mm, coriaceous, not striate, glabrous, eglandular, indehiscent; stipe <10 mm long, apex narrowing to a spine-like beak 10-20 mm long. Seeds uniseriate, imbedded in a yellowish pulp, pale to reddish brown, ovoid to ellipsoid, slightly flattened, 7-9 by 4-6 mm, smooth; pleurogram oblong to U-shaped 2.1-3.3 mm across. Flowers: January-April. Chromosome number: Not determined. Distribution: In disturbed thorn-scrub vegetation, near sea level, in eastern Quintana Roo, particularly in Municipio de Carrillo Puerto and Municipio isla Mujeres. An unusual feature of this hybrid is that it contains the rare lupine derivative resinone, which was isolated from the bark (Pech et al., 2002).

We thank curators of herbaria that made specimens available for study, the National Science Foundation (NSF-BSR-82-15274, NSF-PCM-82-17114, NSF-DEB-04-15803), and the American Philosophical Society (1992). T. W. Dickinson provided program Gower6, BASIC software for calculation of Gower's coefficients.

Appendix

Specimens Examined--Vachellia x cedelloi: MEXICO. Quintana Roo: Km 6.5 carretera Vigia Chico-F. Carrillo Puerto, 8 m elevation, 9 April 1986, R. Villanueva 714 (isotype, XAL); Km 8 de Vigia Chico a Carrillo, 25 January 1984, R. Duran and I. Olmsted 766 (MO, XAL).

Vachellia cornigera: MEXICO. Puebla: El Ojito, Mpio. de Pantepec, 10 June 1980, P. Basurto and G. Duran 602 (MO). Quintana Roo: 12 km E La Pantera, 5 August 1982, E. Cabrera and H. de Cabrera 3351 (MO); en Estero Franco, a 7 km N La Union, 7 May 1980, O. Tellez and E. Cabrera 2111 (MO). San Luis Potosi: at El Banito, 7 miles S Valles, 200 feet elevation, 26 June 1940, W. C. Leavenworth 197 (MO); Barrio de San Juan, 19 July 1937, M. T. Edwards 600 (MO); Tabasco: 7 km E Frontera, 15 m elevation, 17 April 1982, R. Fernandez and N. Zamudio 1022 (MO). Veracruz: Estacion de Biologia Tropical Los Tuxtlas, 100 m elevation, 27 April 1984, G. Ibarra M., S. Sinaca C., and G. Gomez V. 1466 (MO); 2 miles S Rio Blanco, highway 145, 6 July 1965, R. H. Maxwell 199 (MO); vicinity of Puerto Viejo, 23-31 May 1910, E. J. Palmer 448 (MO); Zacupan, July 1917, C. A. Purpus 7748 (MO); near Salinas on route 180, 20 May 1991, D. Seigler, J. Ebinger, H. Clarke, and K. Readel 13525 (EIU); 16 miles N Terra Blanca on route 140, 21 May 1991, D. Seigler, J. Ebinger, H. Clarke, and K. Readel 13549 (EIU). GUATEMALA. Retalhuleu: 9 km N Champerico, 40 m elevation, 15 May 1970, W. E. Harmon 2294 (MO). San Marcos: Puente Talisman, 11 January 1965, D. H.Janzen 1045 (MO). NICARAGUA. Granada: Puerto de Asese, 40-50 m elevation, 31 January 1981, P. Moreno 6390 (MO); Managua: camino a Puertas Viejas-Santa Juana, 8 June 1983, M. Araquistain 3561 (MO); Masaya: Parque Nacional Volcan Masaya, 135-145 m elevation, 31 March 1980, W. D. Stevens, M. Guzman, and D. Castro 16862 (MO); Matagalpa: Hacienda El Ojoche, 19 May 1980, M. Guzman and D. Castro 85 (MO).

Vachellia globulifera:BELlZE. Cayo:ChaaCreek,5km S del camino San ignacio, 7 March 1985, E. Cabrera, P. Cowan, and R. Duran 7705 (MO); Vaca, 2 March 1938, P. H. Gentle 2275 (MO). GUATEMALA. Peten: San Miguel, Lake Peten Itza, 3 February 1968, E. Contreras 7519 (MO); Agua Caliente, 28 March 1922, J. M. Greenman and M. T. Greenman 5947 (MO); shore E of San Jose, Lake Peten Itza, 22 January 1962, C. L. Lundell 17230 (MO). HONDURAS: Yoro: Yoro, 26 January 1934, J. B. Edwards P-746 (MO); MEXICO: Campeche: Zona Arqueologica de Chicana, 15 February 1988, E. Cabrera and H. de Cabrera 15521 (MO); en el Centro Regional de Calakmul, 16 March 1983, E. Cabrera, T. P. Ramamoorthy, J. L. Godinez, and H. de Cabrera 4427 (MO); Quintana Roo: en San Jose de la Montana, 21 March 1983, E. Cabrera, J. L. Godinez, and H. de Cabrera 4504 (MO). Yucatan: Silam, April 1895, G. F. Gaumer 655 (MO); port of Silam, April 1985, G. F. Gaumer 1909 (MO).

Characters used in multivariate analyses ofVachellia x cedilloi, V. cornigera, and V. globulifera complex--1) Symmetry of stipular spine, 1 = symmetrical, 2 = asymmetrical. 2) Number of petiole glands, 1 = mostly solitary and at or just below the lower pair of pinna, 2 = 3-6 present along the petiole. 3) Shape of rachis gland, 1 = canoe-shaped, 2 = narrow volcano-shaped, 3 = columnar. 4) Pubescence of rachis gland, 1 = glabrous or nearly so with obvious striations, 2 = densely puberulent, striations not obvious. 5) Number of pairs of pinna on the largest leaves. 6) Distance between leaflets in mm. 7) Length of leaflet in mm. 8) Width of leaflet in mm. 9) Venation of leaflet, 1 = obvious, 2 = not obvious. 10) Shape of inflorescence, 1 = globose, 2 = short cylindrical, 3 = long cylindrical. 11) Length of inflorescence in mm. 12) Thickness of peduncle, 1 = 0.5-1.0 mm, 2 = 1.2-2.0 mm, 3 = >2.0 mm. 13) Apex of floral bract, 1 = tailed, 2 = circular. 14) Ratio of calyx:corolla lengths, 1 = nearly the same, 2 = 1.5-2 times longer. 15) Shape of calyx shape, 1 = cylindrical, 2 = cone-shaped. 16) Length of filament of stamen in mm.

Literature Cited

EBINGER, J. E., AND D. S. SEIGLER. 1987. Introgressive hybridization in Mexican populations of Acacia macracantha and Acacia pennatula (Fabaceae, Mimosaceae). Bulletin of the International Group for the Study of Mimosoideae 15:73-85.

EBINGER, J. E., AND D. S. SEIGLER. 1992. Ant-acacia hybrids of Mexico and Central America. Southwestern Naturalist 37:408-414.

JANZEN, D. H. 1974. Swollen-thorn acacias of Central America. Smithsonian Contributions to Botany 13:1-131. Legendre, L., and P. Legendre. 1983. Numerical ecology. Elsevier Scientific Publishing, Amsterdam, Netherlands.

MASLIN, B. R., AND C. H. STIRTON. 1997. Generic and infrageneric classification in Acacia (Leguminosae: Mimosoideae): a list of critical species on which to build a comparative data set. Bulletin of the International Group for the Study of Mimosoideae 20:22-44.

PECH, G. G., W. F. BRIRO, G. J. MENA, AND L. QUIJANO. 2002. Constituents of Acacia cedilloi and Acacia gaumeri: revised structure and complete NMR assignments of resinone. Zeitschrift fur Naturforschung 57:773-776.

PODANI, J. 1999. Extending Gower's general coefficient of similarity to ordinal characters. Taxon 48:331-340.

RICO ARCE,M. DE L. 1994. Nueva especie mirmecofila de Acacia (Leguminosae) de la peninsula de Yucatan, Mexico. Acta Botanica Mexicana 26:7-10.

ROHLF, F. J. 2000. NTSYSpc. Numerical taxonomy and multivariate analysis system. Version 2.1. Exeter Software, Setauket, New York.

SEIGLER, D. S., AND J. E. EBINGER. 1988. Acacia macracantha, A. pennatula, and A. cochliacantha (Fabaceae: Mimosoideae) species complexes in Mexico. Systematic Botany 13:7-15.

SEIGLER, D. S., AND J. E. EBINGER. 1995. Taxonomic revision of the ant-acacias (Fabaceae, Mimosoideae, Acacia, series Gummifer ae) of the New World. Annals of the Missouri Botanical Garden 82:117-138.

SEIGLER, D. S., AND J. E. EBINGER. 2005. New combinations in the genus Vachellia (Fabaceae: Mimosoideae) from the New World. Phytologia 87:139-178.

Submitted 7 December 2009. Accepted 10 May 2012.

Associate Editor was Janis K. Bush.

John E. Ebinger * and David S. Seigler

Emeritus Professor of Botany, Eastern Illinois University, Charleston, IL 61920 (JEE)

Department of Plant Biology, University of Illinois, Urbana, IL 61801 (DSS)

* Correspondent: lujastro@yahoo.com
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Title Annotation:Notes
Author:Ebinger, John E.; Seigler, David S.
Publication:Southwestern Naturalist
Article Type:Report
Geographic Code:1MEX
Date:Sep 1, 2012
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