XVI International Botanical Congess

The evolution of Isoetales sensu DiMichele and Bateman spans much of the history of vascular plant evolution, from the Late Devonian to current day Isoetes. While the best known fossil isoetaleans are the arborescent lepidodendrids that dominated the Late Carboniferous, simpler unbranched forms with elongate stems predated, coexisted with, and postdated the coal swamp trees, extending well into the Mesozoic. A suite of novel features including monolete microspores, sunken sporangia and elaborate ligules evolved within long-stemmed Triassic forms. The modern Isoetes plant habit that lacks stem elongation began at least by the Jurassic and characterizes late Mesozoic and Cenozoic isotaleans.