A Morphological Analysis of Three Closely Related Grass Subfamilies

Phytoliths, silica bodies formed within and around plant cells, are a key part of a plant’s physiological structure that can vary in shape between species. These phytolith shapes (socalled morphotypes) can be found abundantly within grasses and vary between taxa within a subfamily either in shape or in their relative abundances and could therefore provide important evolutionary data on how specific grass subfamilies may be related. Previous work has been done on certain grass subfamilies, including Bambusoideae, to identify similarities and differences in shape within a grass subfamily. This study aims to investigate the distribution of phytolith morphotypes among three closely related grass subfamilies (Arundinoideae, Danthonioideae, and Micrairoideae). To collect this data, we conducted a morphological study on over 300 phytoliths in samples from many species within our three subfamilies. The samples were taken from leaf clearings wherein the phytoliths were isolated through chemical treatment and centrifuging to remove other organic material before staining. Samples are imaged using a confocal microscope and then patched together with computer processing to form three- dimensional phytolith images. These sample objects were compared based on phytolith morphotype three-dimensional shape, their relative abundance, location in plant tissues, and size. In addition to the morphological study of individual phytoliths, we studied cleared leaves to obtain a greater sense of the composition of morphotypes within the tissue of the grasses. The results are expected to show an overlap in similar phytolith morphotypes across clades that have similar ecological niches such as photosynthetic systems. Overall, this research aims to find a link between these three close modern subfamilies that could be compared to fossil phytoliths in order to document their evolutionary history and past distribution.