Phylogenetic Relationships Within and Delimitation of the Cosmopolitan Flowering Plant Genus Stellaria L. (Caryophyllaceae): Core Stars and Fallen Stars

Abstract

Abstract—Stellaria (Caryophyllaceae, tribe Alsineae) is a cosmopolitan genus of herbaceous plants that heretofore has lacked a stable estimate of total number of species. Here, we attempted to sample all species currently recognized under the name Stellaria to determine which belong to a core Stellaria genus versus which are masquerading under this name and are instead more closely related to one of several outgroup lineages. Phylogenetic relationships inferred with RAD loci were recovered with generally high levels of support, regardless of age of specimens (here up to 98 yr) utilized for molecular work. Analyses resolved a monophyletic, core radiation of Stellaria that is sister to Cerastium and others. Within core Stellaria, of which we sampled ca. 87% of species, we recovered five primary lineages. However, current infrageneric hypotheses are incongruous with phylogenomic data, and most morphology-based infrageneric hypotheses break down in light of these results. Outside of core Stellaria we recovered numerous other species currently ascribed to Stellaria that are in need of revised generic placement. Based on current results, however, we propose several new taxonomic and nomenclatural renovations within core Stellaria and external to this group as contribution towards stabilization of generic boundaries in Alsineae. These modifications include description of a new genus of Caryophyllaceae from eastern Asia, Nubelaria, as well description of a new genus, Rabelera, to accommodate the lineage previously and more widely known as Stellaria holostea. Nine new combinations are proposed in the genera Adenonema, Cerastium, Mesostemma, Nubelaria, Rabelera, and core Stellaria. Additionally, one new status, one new synonymy, and lectotypes for four species are proposed. We estimate core Stellaria to consist of approximately 112 species, a decrease from many other published species counts. Our results lay a robust foundation for future evolutionary, phylogenetic, and morphological comparisons within Stellaria and among relatives.