The remarkable stomata of horsetails (Equisetum)

Horsetails are an ancient group of land plants that possess many unusual features, including the structure and development of the apertures (stomatal pores) in the epidermis. In addition to a symmetric pair of guard cells, stomata in Equisetum are delimited by an overlying pair of neighbour cells with characteristic vault-like radiating thickenings. Stomatal development involves a well-defined series of asymmetric and symmetric mitoses.

The results of Cullen and Rudall contribute to our understanding of the diverse patterns of stomatal development in land plants. They add to a considerable catalogue of highly unusual traits of horsetails – one of the most evolutionarily isolated land-plant taxa.