Phylogeny, biogeography, reticulation, and classification of <i>Agrostis</i> (Poaceae: Pooideae: Poeae: Agrostidinae) with expansion of <i>Polypogon</i> to include <i>Lachnagrostis</i> (in part)

Abstract To investigate the evolutionary relationships and biogeographical history among the species of Agrostis and allied genera within the subtribe Agrostidinae, we generated a phylogeny based on sequences from nuclear ribosomal DNA (ITS) and three plastid regions ( rpl32‐trnL spacer, rps16‐trnK spacer, and rps16 intron). We also aimed to assess the generic limits of Agrostis , characterize possible subgeneric relationships among species in the genus, identify hypothesized reticulation events, and present our biogeographical theory. Based on our phylogeny of 198 samples, representing 138 species (82 from Agrostis as currently recognized, 10 from Polypogon , and 10 from Lachnagrostis ), we identify two strongly supported clades within Agrostis : clade Longipaleata ( Agrostis subg. Vilfa ) and clade Brevipaleata ( A . subg. Agrostis ). The species of Agrostis in clade Longipaleata usually have florets with paleas 2/5 to as long as the lemma, whereas species in clade Brevipaleata have florets with paleas less than 2/5 as long as the lemma, minute, or absent. Core (species with congruent alignment using ITS and plastid data) phylogenetic analysis of Agrostis reveals three strongly supported clades within Longipaleata (European‐Northwest African, Asian, and African), three strongly supported clades within Brevipaleata (Asian, North American, and South American), and a European grade leading to the latter two. Of the six genera commonly associated with Agrostis , that is, Bromidium , Polypogon, Lachnagrostis, Linkagrostis, Chaetopogon, and Chaetotropis , only Polypogon maintained its status as a separate genus, while the remaining genera are subsumed within Agrostis or Polypogon . Polypogon is identified as an intergeneric hybrid originating via ancient hybridization between unknown representatives of Agrostis clade Longipaleata (plastid DNA) and Calamagrostis clade Americana (nrDNA). We include several species of Lachnagrostis , including the type ( L. filiformis ), that follow the same pattern in Polypogon , while the remaining species of Lachnagrostis in our study are identified as ancient intersubgeneric hybrids within Agrostis . We propose nine new combinations in Polypogon : P. adamsonii (Vickery) P.M. Peterson, Soreng &amp; Romasch.; P. aemulus (R. Br.) P.M. Peterson, Soreng &amp; Romasch.; P. billardierei (R. Br.) P.M. Peterson, Soreng &amp; Romasch.; P. bourgaei (E. Fourn.) P.M. Peterson, Soreng &amp; Romasch.; P. filiformis (G. Forst.) P.M. Peterson, Soreng &amp; Romasch.; P. littoralis P.M. Peterson, Soreng &amp; Romasch.; P. exaratus (Trin.) P.M. Peterson, Soreng &amp; Romasch.; P. polypogonoides (Stapf) P.M. Peterson, Soreng &amp; Romasch.; and P. reuteri (Boiss.) P.M. Peterson, Soreng &amp; Romasch. We designate lectotypes for the names Agrostis sect. Aristatae Willd., Agrostis barbuligera Stapf, A. bourgaei E. Fourn., A. eriantha Hack., A. exarata Trin., A. lachnantha Nees, A. polypogonoides Stapf, Chaetotropis chilensis Kunth, Polypogon elongatus Kunth, P. inaequalis Trin., P. suspicatus Willd., and Vilfa muricata J. Presl .