Taxonomy of Cryptic Isoëtes Species from the Brazilian Semi-Arid Region, with a Note about the Putative Maternal Origin of Polyploids

Abstract. Revealing the unrecognized diversity within cryptic species has profound implications in the taxonomy, systematics, evolutionary studies, and species protections throughout plant groups. Isoëtes is prone to a high rate of cryptic speciation because of its morphological simplicity, stasis, and convergence. Phylogenetic studies revealed cryptic species in the genus from the Brazilian semi-arid region (the Caatinga), which comprises the least studied and most endangered flora in Brazil. Here we conducted morphological analyses and chromosome counts, and took advantage of phylogenetic analyses already published for the genus to provide a taxonomic revision of Isoëtes from the Caatinga. Isoëtes anamariae and I. harleyi are two new species, which were revealed by molecular data and subtle morphological characters. This study provides descriptions, chromosome counts, illustrations of the most important morpho-taxonomic characters of species from the Caatinga, and a key to identify them. All species from this region are diploid and we show the importance of diploids in detangling the origin of polyploids in Brazil.