In mature grass leaf blades as seen in cross-section, oblong cell-like structures have been interpreted most recently as intercellular gas spaces delimited by successive collapsed fusoid cells. These cells have been reported in at least seven of 12 subfamilies of Poaceae and are considered a synapomorphy for the family; however, no developmental work has been performed to verify their meristematic origin or to assess possible homologies within the graminid clade (= Flagellariaceae + [(Joinvilleaceae + Ecdeiocoleaceae) + Poaceae]) or among subfamilies of Poaceae
In this developmental study, which includes a phylogenetically-based sampling approach, Leandro et al. demonstrate that one apparent fusoid cell is typically a cavity resulting from the collapse of the initial fusoid cell and its internal divisions (derivatives). Fusoid cells in all studied Poaceae species are homologous, originating from the ground meristem, and they may play a role in the synthesis and storage of starch granules at early stages of development.
Leandro, T. D., Rodrigues, T. M., Clark, L. G., & Scatena, V. L. (2018). Fusoid cells in the grass family Poaceae (Poales): a developmental study reveals homologies and suggests new insights into their functional role in young leaves. Annals of Botany. https://doi.org/10.1093/aob/mcy025