ABSTRACT
Pollen morphology of neotropical species of Podostemum (Malpighiales: Podostemaceae). Pollen morphology of neotropical species of Podostemum is described for the first time with light (LM) and scanning electronic microscopes (SEM), using pollen dehydration by critical point. Herbarium specimens under study are P. comatum, P. distichum, P. muelleri and P. rutifolium. Pollen grains are dispersed in dyads. Observed with LM, dyads range from 21 to 31μm in lengh and 12 to 18μm wide. Individual pollen grains are radially symmetrical spheroidal to subprolate, and have a tricolpate aperture. The exine is tectate, psilate, with an infratectal structure formed by simple columella under the tectum. With SEM, an abundant pollen surface coat is observed all over the pollen grains, mainly in the two grains dyad contact zone. This pollen coat would protect the grains from dehydration because the environments in which these plants grow have important water variation and pollination is not zoophilic. The shared dyad wall shows bridges that partially fusion the exines, forming calymate dyads. Some dyads bear the apertures aligned between grains and some not. The transverse condition of the aperture or aperture in "L" that occurs in the four studied species is described for the first time. It is interpreted as a trend of the genus to espiroaperture. This change in the aperture would be associated with phenology because it is a genus with very short flowering and anthesis, generally a day of anthesis in the dry season. The spiroaperture increases the chances of germination sites and would also have a harmomegata role in an environment with water changes favoring the reproductive success.Walls have a microechinate sculpture, with or without pads at the base of the microechinae. Size of ornamental processes differs, and the colpus membrane has similar ornamentation to that of the non apertural wall, but with larger processes. Individual morphology of pollen grains is similar to that described for other family genera as Apinagia and Mourera. During previous stages of anthesis, the presence of cross tetrads was observed, also a new contribution for this genus. Rev. Biol. Trop. 58 (1): 81-88. Epub 2010 March 01.
La morfología del polen de cuatro especies neotropicales del género Podostemum (Podostemaceae) se describe aquí por primera vez mediante microscopía de luz y electrónica de barrido, utilizando material deshidratado en punto crítico. Se analizaron ejemplares de P. comatum, P. distichum, P. muelleri y P. rutifolium. Los granos de polen son dispersados en díades. Se encuentra abundante cobertura polínica, principalmente en la zona de contacto entre los dos granos de la díada. En la pared compartida entre los granos se presentan puentes de ectexina que fusionan parcialmente las exinas. Los granos individuales son radialmente simétricos y tricolpados. En algunas díades las aberturas están alineadas entre los granos y en otras no. Se describe por primera vez la condición abertura transversal, que fue observada en las cuatro especies estudiadas, y que se interpreta como tendencia del género a espiroabertura. La escultura de la exina es microequinada con mamelones en la base. Los procesos ornamentales son de diferente tamaño. La membrana del colpo tiene una ornamentación similar a la pared adyacente del grano, pero los procesos tienen mayor tamaño. Se observaron tétrades decusadas en las etapas previas a la antesis, un dato hasta el momento no registrado para el género.