Fusoid cells are large, gas-filled, thin-walled mesophyll cells of previously unknown function that occur within the basal grasses and bamboos. Study of sun-shade leaf variation in three woody bamboo species revealed not only the expected general suite of adaptations (thicker, smaller sun leaves with closer vein spacing, and thinner, larger shade leaves with wider vein spacing), but also that at least in some species fusoid cells develop normally in shade leaves but do not develop in sun leaves. Presence of fusoid cells is associated with broad leafed, forest-dwelling grasses, but sun-shade differences in the development of fusoid cells were noted even within an individual plant, indicating an environmental as well as a genetic component to their development. This strong correlation between shade and the development of fusoid cells suggests a possible role of fusoid cells in light distribution within shade leaves. Our data showed that leaves with normal gas-filled fusoid cells absorbed more light than those infused with mineral oil, supporting the novel proposal that one function of fusoid cells is to increase light absorption through the mechanism of intracellular reflectance. Further investigation should be addressed to quantifying the enhanced light absorption in leaves containing fusoid cells and to assessing the taxonomic distribution of facultatively occurring fusoid cells.

Key words: bamboos, fusoid cells, light trapping, Poaceae, sun-shade leaf anatomy