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Light Environment and Epidermal Cell Morphology in Grasses

Premise of research. Phytoliths (bio-opal) of grasses are preserved in the fossil record and constitute the best method to study grasses and grassland evolution in deep time. However, methods currently used to reconstruct habitat openness based on grass phytolith abundance are potentially biased because of the prolific production of phytoliths in grasses compared to other plants, both herbaceous and woody (ferns and dicots). On the basis of relationships observed in eudicot epidermal cells, we hypothesized that the shape (undulation) and size of epidermal cells (and phytoliths derived from them) will vary with irradiance. This variation could be used to develop a proxy for habitat openness in the fossil record.

Methodology. We grew five species of grass under four irradiance levels and measured epidermal cell parameters, including undulation, area, length, and width, along with gross leaf morphology.

Pivotal results. ANOVA statistical tests showed that with the exception of the shade-adapted Chusquea, the grass species grown demonstrated increased cell length and cell area in shaded treatments, irrespective of leaf dimensions; however, there was no significant change in undulation for either long or short cells.

Conclusions. Grasses do not display changes in epidermal cell undulation with irradiance, as documented in some dicotyledons. However, epidermal cell length and area for long cells and crenate and polylobate short cells do vary with irradiance. Although grasses demonstrate inter- and intraspecific variation, differences in cell length and area may be useful characters for tracking changes in ancient light regime and canopy cover from fossil phytolith assemblages.