How Are Systematics and Biological and Ecological Features Related to Silica Content in Plants? A Study of Species from Southern South America

Premise of research. Plant silica content depends on the phylogenetic position of a taxon; however, biological or ecological factors may also affect it. In this work, we analyzed data on silicophytolith content from 105 species of South America, examining, in a phylogenetic context, its relationship with anatomy and ecological features such as life cycle, growth form, plant origin, and environmental preferences. Methodology. Data on the silicophytolith content and bioecological features of the species were obtained from published and unpublished sources. The relations between systematics, silica content, and bioecological variables were analyzed through measurements of phylogenetic signal and phylogenetic generalized least squares regressions. Pivotal results. Eighty-six percent of the species produced between 0.38% and 19% of silicophytolith dry weight in leaves. Silica content was variable between and within clades. Values of lambda and K indicate a low phylogenetic signal for the variable silica content. Dicotyledons accumulated silica in typical epidermal cells, and a few families also stored it in cystoliths. Most of the monocot families showed high silicophytolith contents and a high diversity of silicified cells. Plant origin affected the silica contents: exotic species accumulated more than native ones. On the other hand, no statistical relationship was found between silica content and the other ecological variables. Conclusions. Silicophytolith accumulation is a common feature in most of the species studied. The low phylogenetic signal of silica content is explained by inter- and intraclade variability, which in turn supports the hypothesis that silicophytolith accumulation is a homoplasic character among plants. On the basis of the overall analysis of silicophytolith content and tissue distribution, high content could be related to the specific accumulation mechanisms and roles of silica. The origin of the plant was the only bioecological variable that influenced plant silica content. This finding may indicate some ecological role for silica in exotic plants involving their success in novel environments.