Disentangling the Phylogeny of Isoetes (Isoetales), Using Nuclear and Plastid Data

Abstract

Premise of research. The heterosporous lycopsids of Isoetes show limited morphological and genetic variation despite a worldwide distribution and the ancient origin of the lineage. Here major relationships within the genus are clarified, using a substantially larger sampling of species than in previous studies. A first assessment of divergence times of clades is made, and the implications for dispersal mechanisms and biogeographic distribution patterns are discussed.Methodology. On the basis of sequences from three gene regions and 109 specimens representing 74 species of Isoetes, phylogeny and node ages were estimated using parsimony and Bayesian inference.Pivotal results. Three rooting approaches (outgroup analysis, midpoint rooting, and clock rooting) coherently resolved a diverse clade containing species from South Africa, India, Australia, and South America (clade A) as sister to remaining Isoetes. Analysis of divergence times of clades yielded a median age of the crown group of 147 million years ago...