A new combination, Guadua chacoensis, is made. Based on morphological evidence, G. chacoensis appears closely allied to G. trinii. A detailed illustration of the species is included, and morphological descriptions and illustrations of the seedling and fruit are provided. Guadua was segregated from the genus Bambusa Schreber and described by Kunth (1822). Important diagnostic characters that distinguish this genus are triangular culm leaves in which the margins of the sheath and blade are usually contiguous, a distinctive band of short white hairs above and below the nodal line, synflorescences with 2to many-flowered pseudospikelets, a palea of firm texture with prominent wings emanating from the keels, and the presence of stomata and papillae on the adaxial surface of the leaf blades (Soderstrom & Ellis, 1987; Soderstrom & Londofio, 1987). Other characters useful in distinguishing among the species of the genus are the shape of culm and foliage leaf, the structure and shape of pseudospikelets, and the habit of the plant. Guadua occurs throughout tropical America, from Mexico to northern Argentina, and contains perhaps 30 species. Along with Guadua, four other genera are placed in the subtribe Guaduinae: Criciuma Soderstrom & Londoiio and Eremocaulon Soderstrom & Londoiio from Brazil, and Olmeca Soderstrom and Otatea (McClure & Smith) Calder6n & Soderstrom, from Mexico (Soderstrom & Ellis, 1987). Guadua chacoensis occurs in northern Argentina, southeastern Bolivia, and southern Paraguay and is one of the three southeasternmost species of the genus. It is frequently misidentified as G. angustifolia Kunth. The species was described in 1918 by the Argentinian botanist Nicolas Rojas Acosta as Bambusa chacoensis. A type specimen was not designated but the locality data (General Vedia, Depto. Bermejo, Prov. del Chaco-Argentina, and Ile de la Colonia Aquino, Rio Paraguay) and the common name "tacuara," distinguish it from two species that occur sympatrically, G. paraguayana Doell, "picanilla," and Guadua trinii (Nees) Ruprecht, "yatevo," "tacuaruzu," or "tacuara brava" (Nicora & Ruigolo, 1987; Young, 1985). McClure (1973), in his annotated checklist of species, included G. chacoensis under the heading of unresolved specific taxa. Young (1985) treated this species as one of two subspecies in the variable Guadua angustifolia Kunth complex and indicated a neotype. However, Young (1985) pointed out that "the two subspecies can be separated using a combination of vegetative and reproductive characters but since the morphological gap separating them is smaller than that separating most species in the subgenus, the taxa are considered here to be only subspecifically distinct." In this study, a comparison of floral and vegetative morphology among G. chacoensis, G. angustifolia, and G. trinii is presented. Based on complete material collected by Camilo Quarin, a botanist from the Universidad Nacional del Nordeste, Corrientes, Argentina, a detailed illustration of the habit of G. chacoensis and descriptions and illustrations of the seedling and fruit are provided. Guadua chacoensis (Rojas) Londofio & Peterson, comb. nov. Basionym: Bambusa chacoensis Rojas, Bull. Acad. Int. Geogr. Bot. 26: 157. 1918. TYPE: Argentina. Chaco: Departamento Bermejo, General Vedia, Riberas del Rio de Oro, 23 July 1974, Quarin et al. 2384 (neotype, designated here, CTES; isoneotypes, F, G not seen, MO, US). Figure 1. Woody, thorny bamboo. Rhizomes pachymorph. Culms 10-20 m tall, 8-15 cm diam., green, erect below and arching apically; internodes hollow; nodes solitary; bud solitary, covered by a prophyll, positioned 2-4 mm above the nodal line. Culm leaves NOVON 2: 41-47. 1992. This content downloaded from 157.55.39.163 on Sat, 19 Nov 2016 04:22:52 UTC All use subject to http://about.jstor.org/terms