Nuclear multi-locus phylogenetic inferences of polyploid Isoetes species (Isoetaceae) suggest several unknown diploid progenitors and a new polyploid species from South America

Polyploidization is a dominant force in shaping the evolutionary history of Isoetes. The genus is globally distributed, with South America harbouring the highest number of known species. Previous phylogenetic studies revealed that most species from South America belong to the American clade, which is the largest but least resolved clade in Isoetes. The clade includes species from South, Central and North America, and has had a complex evolutionary history. To elucidate phylogenetic relationships in this clade, we analysed sequences of the second intron of the LEAFY homologue (LFYint2) and the nuclear ribosomal ITS region (nrITS). In this study, we aim to elucidate the phylogenetic relationships of Isoetes spp. from the American clade, focusing on those from south-eastern Brazil, and to identify the putative progenitors of polyploid species that occur in this region. The results of our study support the distinctness of allopolyploids and allow us to identify several unknown progenitor lineages. The distinctness of the allotetraploid I. caparaoensis is confirmed, so we describe it here as a new species, accompanied by an illustration and comments. Our study is one of the first to elucidate the origin of polyploid taxa among lycopods in South America.