A new species of Podostemaceae, Marathrum rubrum, from Jalisco, Mexico, is described and illustrated. Capillaceous leaf divisions and red leaf color distinguish M. rubrum from other species. RESUMEN. Se describe e ilustra una especie nueva de la familia Podostemaceae (Marathrum rubrum) del estado de Jalisco, Mexico. Las divisiones capiliformes y el color rojizo de las hojas distinguen a M. rubrum de las otras especies. The pantropical Podostemaceae are the largest family of aquatic flowering plants. Little taxonomic work has been conducted on New World Podostemaceae since Royen's treatments (1951, 1953, 1954). Currently most species of Podostemaceae in the New World are poorly collected, taxonomic boundaries at both the specific and generic levels are unclear, and factors relating to the unusually high incidence of endemism (e.g., > 45% among New World species) are unresolved. Marathrum, one of the largest genera of Podostemaceae, is composed of 25 species occurring in tropical river rapids and waterfalls. The genus ranges from the West Indies and Mexico through Central America, to northwestern portions of South America (Royen, 1951). During field studies aimed at clarifying the taxonomy of Podostemaceae in Mexico, collections were made from Jalisco that did not correspond to any described species. These collections serve as the basis for the description of a new species, Marathrum rubrum Novelo & Philbrick. Marathrum rubrum Novelo & Philbrick, sp. nov. TYPE: Mexico. Estado de Jalisco: municipio de Cabo Corrientes, Puente Los Horcones sobre el rio, a 27 km al S de Puerto Vallarta rumbo a Chamela, 6 Mar. 1991, Novelo & Philbrick 1003 (holotype, MEXU; isotype, RSA). Figure 1. Herbae caule longo, prostrato, applanato; lamina iterum atque iterum pinnata, divisionibus ultimis capilliformibus, 2-4.5 mm longis, 0.02-0.06 mm latis, rubescentibus, apice acutis. Flores solitarii, axillares, pedicellati; pedicelli apice expanso, cupulato, cupula 1.5-2 mm diametro. Tepala triangularia, filamentis alternantia. Stamina 7-9 in verticillo, libera, pistillum cingentia. Antherae 1.52.8 mm longae. Styli liberi, conici. Fructus 4.5-5(-6) mm longus, 2 valvis, quaque 3-costata. Aquatic herbs usually with a long prostrate and flattened stem up to 1 cm diam., strongly adhering to rocks. Leaves alternate, up to 20 cm long, petiole 2.5-9 cm long, cylindrical, up to 0.8 mm diam., with a broadened base; blade repeatedly pinnate, the later divisions capillaceous, 2-4.5 mm long, 0.02-0.06 mm wide, apex acute. Flowers hermaphroditic, actinomorphic, pedicellate, borne singly, axillary, protected by a spathella; spathella 0.72 cm long, thin, clavate. Pedicels 3-5.5 cm long, elongating during anthesis, with an expanded apex forming a cuplike process around the capsule base, cup 1.5-2 mm diam., with irregular border. Tepals 0.5-0.9 mm long, triangular, alternating with the stamens. Stamens 7-9, free, in a ring surrounding the pistil; filaments 2.3-4(-9) mm long, subulate, flattened, elongating during anthesis, deciduous; anthers 1.5-2.8 mm long, sagittate, basifixed, 2-celled, dehiscing longitudinally by 2 lateral slits. Ovary superior, ellipsoid, 2-locular; styles 2, 0.6-1.5 mm long, free, conical, ovules numerous, placenta axile. Fruit 4.5-5(-6) mm long and 1.7-2.2 mm diam., 2-locular capsule, suture margins thickened; valves 2, subequal, each 3-ribbed, one of them deciduous. Seeds 0.25-0.30 mm long, 0.12-0.18 mm wide, 574 (SD 317, N = 20) per capsule, obovoid. Pollen 14.5 um (SD 0.8, N = 30) diam., tricolpate, tectum spinulose. Paratypes. MEXICO. Jalisco: Municipio de Cabo Corrientes, Rio Horcones, aprox. 17 km S de Puerto Vallarta rumbo a Chamela, 6 Feb. 1991, Novelo 979 (MEXU, RSA); Puente Los Horcones sobre el rio, a 27 km al S de Puerto Vallarta rumbo a Chamela, 6 Feb. NOVON 3: 456-458. 1993. This content downloaded from 207.46.13.111 on Tue, 09 Aug 2016 05:30:22 UTC All use subject to http://about.jstor.org/terms Volume 3, Number 4 1993 Novelo & Philbrick
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