DNA sequence data use in phylogenetic analysis of eastern North American stitchworts

<p>Generic delimitation in Caryophyllaceae has been a challenge, and has been informed most recently by use of molecular phylogenetic data. In this study, analysis of 29 samples from the small segregate <em>Mononeuria</em> using nuclear ITS and plastid <em>rps16</em> data revealed it to be polyphyletic. The type species <em>Mononeuria patula</em> as well as two others (<em>M. muscorum</em> and <em>M. paludicola</em>) were shown to belong to the <em>Sabulina</em> clade. The remaining species formed a clade that also included the previously monotypic <em>Geocarpon</em> and was sister to a heterogeneous group that included the Hawaiian <em>Schiedea</em> and three other monotypic genera, <em>Honckenya</em>, <em>Wilhelmsia</em>, and <em>Triplateia</em>. Although several nomenclatural options are available, we propose to place the species from this clade into a single genus, <em>Geocarpon</em>, which basically follows the most recent treatment after exclusion of <em>Sabulina</em> species, but with the necessary new genus placements. New combinations are proposed: <em>Sabulina muscorum</em>, <em>Sabulina paludicola</em>, <em>Geocarpon carolinianum, Geocarpon cumberlandensis</em>, <em>Geocarpon glabrum</em>, <em>Geocarpon groendlandicum</em>, <em>Geocarpon nuttallii</em>, and <em>Geocarpon uniflorum.</em> Analysis of the sequence data revealed remarkable variability among populations of <em>Sabulina</em> (formerly <em>Mononeuria</em>) <em>patula</em>, <em>Sabulina</em> (formerly <em>Mononeuria) paludicola</em>, and <em>Geocarpon </em>(formerly <em>Mononeuria</em>) <em>groenlandicum</em>, suggesting that cryptic species may be present. The data also suggested that broader sampling of <em>Sabulina</em> and <em>Geocarpon</em> could lead to increased understanding of the timing and origins of occupation of calcareous glades and rock outcrop habitats in eastern North America.</p>