Ontogeny of fusoid cells in Guadua species (Poaceae, Bambusoideae, Bambuseae): evidence for transdifferentiation and possible functions

•Fusoid cells have different interpretations depending on authors.•We document changes experimented by arm cells to differentiate into fusoid cells.•Structural and ultrastructural studies were performed with LM and TEM.•Fusoid cells in Guadua species uniformly collapse, delimiting intercellular spaces.

Fusoid cells have been interpreted as cells or intercellular spaces, according to different authors. Here, structural and ultrastructural evidence is provided relative to the origin and changes experimented by chlorenchyma cells (“arm cells”) to differentiate into fusoid cells with large intercellular spaces between them. Performed studies and observations were made using Light and Transmission Electron Microscopy. Fusoid cells in Guadua species die but do not remain intact; instead, they uniformly collapse, delimiting conspicuous intercellular spaces which are bigger and different in shape from these cells. In transverse sections of mature and expanded bamboo leaf blades, usually seen in anatomical descriptions, the so-called “fusoid cells” are actually conspicuous intercellular gas spaces delimited by successive collapsed (and rarely not collapsed) fusoid cells. Also, we hypothesize possible relations or links between fusoid cell shape, structural function and apoplastic transport in bamboo leaves.