Morphology and ultrastructure of heterosporous Filicophyta spores from north‐west Argentina

Abstract

Mega‐ and microspores of heterosporous Filicophyta (Azolla cristata Willd., A. filiculoides Lam., Marsilea ancylopoda A. Braun, M. mollis Rob & Fern. and Salvinia minima Baker) that grow in north‐west Argentina were studied by stereo microscopy, light microscopy, scanning electron microscopy and transmission electron microscopy. The spores of Salvinia minima were analyzed for the first time. The mega‐ and microspores morphology and sporoderm structure as well as the type of microspore aggregation enable determination of the taxa at generic level, and at specific level in Azolla. Both species of Azolla can be differentiated by their megaspore surface and wall ultrastructure. The microspore ornamentation in Marsilea is variable even within the same sporocarp. These differences could be related to different stages in spore maturation.