Reference collection of plant phytoliths from the Caatinga biome, Northeast Brazil

Located in northeastern Brazil, the Caatinga biome is characterized by a semi-arid climate with vegetation adapted to high temperatures, low precipitation and uneven rainfall distribution throughout the year. The unjustified belief that the Caatinga ecosystem is poor in biodiversity and endemism, makes it the most undervalued and botanically unknown Brazilian biome, despite there being several phytogeographical areas, and a significant number of rare endemic taxa. Phytoliths are biomineralizations of silica (Si) that precipitate inside or between plant cells during the process of photosynthesis or evapotranspiration, giving the plant organism a series of benefits and evolutionary advantages. In this study, 33 species from 16 different families typical to the region were analyzed, in order to establish modern reference collections enabling further environmental reconstitution studies using phytoliths as proxy, contributing, therefore, to improved knowledge on the Caatinga biome. The results showed that Caatinga plants produce a large amount of biomineralizations, the most prevalent being tracheids, followed by polyhedral, globular granulate, elongate and trichomes (lanceolate hair cells), among others. The types of silicification found may be related to the environmental characteristics of the Caatinga, whereby plants develop mechanisms against desiccation. The deposition of Si in plant cells may be a survival strategy in this environment. Despite some limitations, phytoliths have been shown to be promising tools for improving knowledge on the vegetation of this region, as well as for use in paleoenvironmental studies in the biome.