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

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