Stomatal Structure and Stomatogenesis in Azolla pinnata R. Brown

A stoma in Azolla pinnata consists of a unicelled, binucleate guard cell with a pore, and one or more subsidiary cells towards the proximal side. Stomatal development is of the polocytic or mesoperigenous anomocytic type except that the guard-cell mother cell fails to form two distinct guard cells because of restricted cytokinesis. Similarities and differences between the stoma of A. pinnata and that of a fossil lycopod, Zosterophyllum myretonianum are discussed.