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Premise of the 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 about silicophytolith content from 105 species of South America, examining, in a phylogenetic context, its relationship with the anatomy and ecological features such as life cycle, growth form, plant origin and environmental preferences.Methodology: Data about silicophytolith content and bio-ecological features of the species were obtained from published and unpublished sources. The relation between systematics, silica content and bio-ecological variables were analyzed through measurements of phylogenetic signal and phylogenetic generalized least-squares regressions (PGLS).Pivotal Results: 86% of the species produced between 0.38% and 19% dry weight of silicophytoliths in leaves. Silica content was variable between and within clades. λ and K values indicate a low phylogenetic signal for the variable silica content. Dicotyledons accumulated silica in typical epidermal cells, and a few families stored it also in cystoliths. Most of the monocot families showed high silicophytolith contents and high diversity of silicified cells. Plant origin affected 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 the inter and intra clade variability, which in turn support the hypothesis that silicophytolith accumulation is a homoplasic character among plants. Based on the overall analysis of the silicophytolith content and their tissue distribution, high content could be related to specific accumulation mechanisms and roles of silica. The origin of the plants was the only bio-ecological variable that influenced in plant silica content. This finding may indicate some ecological role of silica in exotic plants, involving the success of them in novel environments.

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