Habitat, Evolution, and Speciation in Isoetes

Species of Isoetes are notorious for the difficulties they present in identification. These difficulties are attributable to a series of habitat adaptations that have resulted in morphological simplicity, homoplasy, and reticulate evolution. Internal air chambers in the leaves of all taxa indicate that primitive Isoetes was aquatic. During the breakup of Gondwana, ancestors of modern taxa appear to have passed through a terrestrialization phase, which was accompanied by development of several morphological novelties and reductions including the evolution of sclerotic phyllopodia. This adaptation appears to have evolved after separation of the Indian subcontinent (...)