Phytoliths of Amazonian grasses: diversity and applications

Resumen

In the Poaceae, silica accumulates in idioblast cells in leaves and other organs, forming bodies called “grass silica short cell phytoliths” (GSSCP). Epidermal cells and hairs can also accumulate silica and are considered phytoliths as well. The GSSCPs are particularly well studied and can be diagnostic at different taxonomic levels, including subfamily. This, and the fact that phytoliths can persist in soils for millions of years, make them useful proxies to characterize plant assemblages in paleoecological and archaeological studies. Over the past decade we have been developing phytolith reference collections of Amazonian taxa to aid in the identification of ancient plant remains from this region. To create a representative Amazonian grass collection, we extracted phytoliths from 150 species (88% of Colombian Amazonian grasses) in 59 genera and seven subfamilies. We identified 12 broad morphotype categories with a total of 54 variants, partitioned into two datasets: GSSCP and other silicified epidermal structures; UPGMA analyses were conducted to test for groupings at subfamily level in the separate and combined datasets. We found diagnostic morphotypes at the genus or even species level in some cases, and also identified silicified epidermal cells in both archaeological and paleoecological samples; however, we found no clear pattern of morphotype distribution at subfamily level, a result that contrasts with GSSCP surveys from other regions. We reiterate calls for more intensive regional sampling to elucidate patterns of variation in both GSSCP and other silicified epidermal structures in grasses.