Panicum aquarum, a New South American Species of Panicum (Poaceae: Panicoideae: Paniceae) Fernando 0. Zuloaga and Osvaldo Morrone Instituto de Botanica Darwinion, Casilla de Correo 22, Isidro (1642), Argentina Previously unidentified specimens from Brazil,Colombia, and Venezuela are recognized as a newspecies of Panicum. This species is described andillustrated exomorphologically and anatomically andis compared with the putative most closely relatedspecies in subgenus Panicum. Panicum aquarumhas a peculiar inflorescence pattern, with prophyllarbranching occurring in several parts of the inflo-rescence. Prophyllar branching has not been citedup to the present in the genus Panicum and is anuncommon feature of the Poaceae.MATERIALS AND METHODS Segments taken from the middle third of thesecond leaf blade of a floriferous culm were usedfor anatomical studies. Specimens were treated withContrad 70 (Schmid & Turner, 1977). The leafmaterial was desilicified, free-hand sectioned, stainedwith safranin and fast green, and mounted in glyc-erin jelly. Epidermis preparations were made follow-ing Metcalfe's (1960) method. Silica bodies, corkcells, and starch grains were identified with liquidphenol (Metcalfe, 1960), Sudan III (Sass, 1940),and IK (Sass, 1940) respectively. Drawings andobservations were made using a Willd M20 micro-scope with camera-lucida. Upper anthecia werestudied with a JEOL, J.S.M. 25SII scanning electronmicroscope (SEM) of the Department of Odontologyof the University of Buenos Aires, Argentina.Panicum aquarum Zuloaga & Morrone, sp. nov. TYPE: Venezuela. Guarico: Dpto. Infante, Par-que Nacional Aguaro-Guariquito, Congriales de la Gorra, entre La Esperanza y Mesa de Cam-bao, ca. 9012'-9�16'N y 67048'-67060'W, 60 m, Dec. 1981, Delascio, Montes & Davidse 11206 (holotype, VEN; isotypes, MO, SI). Fig-ures 1, 2. Culmi 0.90-1.30 m alti, paniculis numerosis ex nodissuperioribus nascentibus, spiculis elipsoideis 3-3.9 mmlongis, gluma inferiore spiculae 1-/ longitudinis ae-quante, gluma superiore ac lemma inferiore subaequali-bus, anthoecio superiore indurato, glabro, brevi, paleaeapice papilloso. Annual?, 0.90-1.30 m high. Culms erect, root-ing at the lower nodes, freely branching at the uppernodes; internodes 7-19 cm long, glabrous, striate,mottled, hollow; nodes glabrous, compressed, brown-ish. Sheaths 8-18 cm long, thin, delicate, glabrous,shiny on the inner surface and with air spaces, themargins membranous. Ligules ca. 1.2 mm long,short-membranous at the base and long-ciliate atthe apex, adaxial surface pilose; collar glabrous.Blades linear, 11-18 cm long, 0.2-0.4 mm wide,the lower ones deciduous, glabrous, narrowed atbase, the margins involute, scaberulous, the mid-nerve manifest toward the base. Inflorescence ter-minal with a peduncle up to 25 cm long, glabrous,scaberulous; panicles lax, pyramidal, multiflowered,35-40 cm long, 12-20 cm wide; axillary paniclesnumerous, smaller and similar to the terminal one;main axis terete, glabrous, the pulvini glabrous;first-order branches alternate or subopposite, diver-gent, the axis of the branches triquetrous, scaber-ulous; second-and third-order branchlets alternatewith scaberulous axis; spikelets congested on third-order branches; pedicels claviform, glabrous. Spike-lets solitary, ellipsoid, 3-3.9 mm long, 1-1.2 mmwide, glabrous, stramineous or tinged with purple,gaping at maturity; upper glume and lower lemmasubequal, acuminate, longer than the upper anthe-cium. Lower glume ovate, abruptly acuminate, 1.7-2.7 mm long, �-34 the length of the spikelet, (3-)5-nerved, the midnerve scaberulous toward the up-per portion; stipe conspicuous between the lowerand upper glume. Upper glume 3-3.6 mm long,acuminate, (5-)7-nerved. Lower lemma glumiform,3-3.2 mm long, (5-)7-nerved. Lower palea oblong-lanceolate, 1.7-2.1 mm long, 0.6-1 mm wide, gla-brous, hyaline; lower flower absent. Upper anthe-cium ellipsoid, 2.1 mm long, 1.2-1.3 mm wide,indurate, stramineous, with black spots at maturity,smooth and shiny, with a brown disc at its base atmaturity; upper lemma 5-nerved, the margins in-volute; upper palea 2-nerved, papillose at the apex.Caryopsis broadly ellipsoid, 1.5 mm long, 1 mmwide, whitish; hilum subbasal, punctiform; embryoV' or less the length of the caryopsis. Paratypes. BRAZIL. AMAZONAS: Munic. Humaiti,7�31'S, 63�10'W, campo a 15-17 km da cidade pela NovoN 1: 185-190. 1991.