Palynology and aspects of reproductive biology of Plagiochila (dumort.) Dumort. (Plagiochilaceae)

Abstract

Plagiochila (Dumort.) Dumort is a group of great importance among bryophytes due to its taxonomic and ecologic implications and it is the richest and more complex genus in Plagiochilaceae, possessing proximally 700 accepted names. Despite the various attempts made to solve taxonomic issues, there are few studies on Plagiochila dealing with palynological and reproductive investigations. Thus, the goals of this dissertation were to develop a palynological study of Plagiochila (Dumort.) Dumort. (Chapter one) and to investigate the strategies regarding the reproductive biology (Chapter two) and desiccation tolerance (Chapter three) of one species belonging to this genus. To develop the palynological study, spores of seventeen species of Plagiochila were analyzed following standard palynological techniques and observed through light and electron microscopy; morphological and ultrastructural data were obtained and interpreted considering their relevance to taxonomy. Plagiochila porelloides was the species selected as model to perform the reproductive biology and water stress tolerance studies. For the first, we assessed the sex ratio and fertilization success to test for sex ratio variation among populations and for possible relationships between the sex ratio and environmental factors. For the latter, field collected healthy plants, among male and female individuals from three different population, were subjected to a desiccation tolerance assay at 40% of RH for a period of 22 h, pursuing fordesiccation tolerance ability and any sex differences in tolerance. Our results demonstrate that the spores were found to be apolar, spheroidal, released in monads, and varying in size from 13μm to 58μm (small to large size). The sporoderm comprises three layers and, based on spore surface ornamentation (variable granules in shape and morphology), species were assembled into four different spore types. Hierarchical cluster analysis using both taxonomic and palynologic information revealed five different groups of species. Regarding the sex ratio, the expressed sex ratios in P. porelloides populations were heterogeneous, having a malebiased ratio (0.375 ♀:1 ♂), and it was associated with fertilization; but no significant relationship was found in relation to any environmental aspects. Concerning to water stress, P. porelloides shoots survived the low RH of 40%, demonstrating that the species is DT; females were found to be more DT than males. Our finds bring important information about spore morphology and reproductive ecology for Plagiochila, revealing the importance of spore description in further phylogenetic studies, and the relevance of sex ratio and sex differences in water stress tolerance to reproductive biology and population dynamics.