Phylogenetics of <i>Piresia</i> (Poaceae: Bambusoideae) reveals unexpected generic relationships within Olyreae with taxonomic and biogeographic implications

Abstract Piresia , a Neotropical herbaceous bamboo genus (Poaceae, Olyreae) including six described species, has a disjunct geographic distribution involving the Caribbean and north/western South America and the northeastern Atlantic Forest in Brazil. Its phylogenetic relationships are poorly known, especially with respect to certain monotypic genera within Olyrinae, such as Reitzia , endemic to the Atlantic forest of southern/south Brazil, and Piresiella , endemic to Cuba. In order to examine the evolutionary history of Piresia , we analyzed 36 samples, including known and possible new species of the genus, as well as members of Reitzia , Piresiella and other genera of subtribes Olyrinae, Parianinae and Buergersiochloinae as the ingroup, and selected woody bamboos and Lolium (Pooideae) as the outgroups. Five regions of plastid and nuclear non‐coding DNA spacers ( trnD‐trnT , trnS‐trnG , rpl32‐trnL , trnH‐psbA , ITS) were sequenced, and to estimate phylogenetic relationships, we used Bayesian inference, maximum likelihood and maximum parsimony considering the plastid regions (with and without gaps) and ITS separately. Surprisingly, Piresiella emerged as sister to the monotypic Buergersiochloa (Buergersiochloinae), endemic to New Guinea. Based on these results and morphological analysis, we discuss the implications for the biogeography of the herbaceous bamboos, formally transfer Ekmanochloa , Mniochloa and Piresiella to Buergersiochloinae, and provide an emended description of the subtribe. Three main lineages were recovered within Olyrinae, one of them comprising Piresia and Reitzia , with high support. Within this clade, the two main lineages are geographically distinct, and their evolutionary history seems to be complex and possibly related to adaptations to climatic conditions. We suggest new directions for future studies involving this clade, in order to better understand its evolutionary history and generic circumscription.