Spore types in Mexican and Mesoamerican species of Pteris L. (Pteridaceae)

Spore morphology of 25 Mexican and Central American species in Pteris were studied. This was accomplished using scanning electron and light microscopy. Spores are trilete, tetrahedral, with plane or slightly convex proximal faces, concave only occasionally, and convex or hemispherical distal faces. In addition to these general features and size, we also considered the following traits: (a) cingulum; (b) presence of a commissural flange; (c) types of macro-ornamentation; (d) ornamentation in distal and proximal faces. In general, distal and proximal faces of Pteris spores are divided by a circumfluent cingulum, lacking ornamentation, infrequently not well defined, or interrupted. The laesura have a commissural flange in almost half of the studied species. The most common macro-ornamentation is muriform, less frequently steliform or buliform. Ornamentation is usually different on both sides of the spore. In most of the studied species occasional to abundant globules are present on the spore surface. The combination of these traits allows us to recognise six spore types, which are described in detail. These spore types disagree with groups of species of Neotropical Pteris previously studied using other characteristics (mainly frond architecture and molecular data). Our results show that the use of spore characteristics can help clarify infrageneric taxonomy in Pteris.