Occurrence of spores from an isoetalean lycopsid of the Polysporia-type in the Late Devonian of Ohio, USA

Thousands of dispersed megaspores of the Valvisisporites auritus-type, some isolated megasporangia still containing them and dispersed microspores of the Endosporites globiformis-type have been found occurring in close association in the Late Devonian (Famennian) of Ohio, USA. Until now, these spores have only been found in the Carboniferous, where they have been shown to have been produced by isoetalean lycopsids assigned to the plant genus Chaloneria and the morphogenus Polysporia. The discovery of dispersed megaspores of the V. auritus-type and microspores of the E.globiformis-type in the Famennian of the USA may indicate that such sub-arborescent lycopsids already existed in the Late Devonian, which thus extends the range of distribution of these taxa, at least in North America. The present work describes, using LM, SEM and TEM, megaspores of V. auritus-type, megasporangia containing these megaspores, and microspores of E.globiformis-type. The comparison with their Carboniferous representatives shows that they are quite similar. This comparative study permits clarification of some ultrastructural features of the megaspores of the Valvisisporites-type, such as the partly lamellate–partly amorphous innermost exospore, demonstrating that this is a characteristic and important ultrastructural feature of this genus.