Morphological variations of lobate phytoliths from grasses in China and the south-eastern United States

Abstract

Phytolith analysis of grasses is a useful tool in palaeoenvironmental and archaeobotanical research. Lobate phytolith is one of the most important morphotypes of grass phytoliths. This study describes morphological variations of diagnostic lobate phytoliths and produces a tentative classification scheme based on 250 modern grass species from China and the south-eastern U.S.A. Eighty-five grass species were found to contain lobate phytoliths. They are derived mainly from Panicoideae, but also include the Chloridoideae, Oryzoideae and Arundinoideae subfamilies. Twenty-five lobate morphological types were observed from different subfamilies, genera or tribes of grasses, based on two important parameters: (1) the length of the lobate shank and (2) the shape of the outer margin of the two lobes. The identification of grass tribe or even genus is possible based on the differences in lobate shape parameters or the composition of assemblages. However, not all of the lobate assemblages have a definite relationship with the genera that produce them, because grasses can only produce a limited range of lobate shapes that often overlap from one genus to another. Several C3 grasses and Chloridoideae subfamily grasses also produce characteristic lobate phytoliths. The variations of lobate morphologies can be related to environmental factors, especially moisture. Typical hygrophytic grasses tend to yield lobate phytoliths with very short shank, whereas typical xerophytic grasses tend to produce lobate phytoliths with a very long shank. The potential link between phytolith morphology, grass taxonomy and environmental conditions opens the possibility that phytolith morphology may be used as a proxy in palaeoclimatic reconstruction.