Format: ORAL

Jovani B. S. Pereira*,1,2, Dietmar Quandt1, Jefferson Prado2

1 Bonn Institute of Organismic Biology (BIOB) - Plant Biodiversity & Evolution, Meckenheimer Allee 170, Bonn, Germany 2 Instituto de Pesquisas Ambientais (IPA), Herbarium SP, Av. Miguel Estéfano 3687, CEP 04301-012, São Paulo, Brazil *Correspondence: jbernar1@uni-bonn.de

Polyploidy is arguably a dominant force shaping the evolutionary histories of many, if not most, plant lineages. It can fuel evolutionary novelties and, in some cases, facilitate speciation and diversification. Among the free-sporing vascular plants, the lycophyte genus Isoetes L. exhibits one of the highest proportions of polyploids, constituting approximately 50% of its species. The globally distributed genus comprises about 250 species, with plants occurring in aquatic environments, fully to partially submerged, and more rarely, terrestrial. Although several phylogenetic studies converge on seven major well-supported clades, the relationships within these clades remain highly unresolved. Since Isoetes polyploids mostly have a hybrid origin, polyploidy poses a confounding factor in phylogenetic analyses. In this study, we employed data from multiple sequencing approaches to elucidate phylogenetic relationships and polyploid origins in recently diverged Isoetes groups in the Neotropics. Using nuclear datasets derived from double-digest restriction-site associated DNA (ddRAD) and PacBio long-read amplicon sequencing, along with organellar data from skimmed genome sequencing, we showed that while polyploidy evolved early in Isoetes, the deep divergences inferred from nuclear and organellar data are identical. On the other hand, relationships in recently diverged groups exhibit strong discordance between organellar and nuclear datasets, reflecting recent hybrid speciation within the genus. Furthermore, ddRAD-Seq data analyses result in well-resolved phylogenetic relationships within the Neotropical species groups. These groups present clear geographical distribution patterns and we discuss the factors that led to their current distribution in the Neotropics. We showcase the robustness of nuclear data in establishing a phylogenetic framework to address evolutionary questions and demonstrate how incongruence between nuclear and organellar data can offer insights into the origin of polyploids. Our findings contribute to a comprehensive understanding of polyploid origins and deepen our insights into the biogeography of the genus in the Neotropics.