The flowering plant genus Stellaria L. (Caryophyllaceae; the “starworts”) numbers around 112 species and exhibits a cosmopolitan distribution. To gain familiarity with the Caryophyllaceae and a broad number of temperate plant taxa overall in the field, I conducted a floristic inventory of the South San Juan Wilderness of southern Colorado, documenting 533 species of mostly native vascular plants present there, including five species of Stellaria. Research on Stellaria beyond Colorado was then conducted across five continents based on field and museum work, with the proximate goal of forming a comprehensive phylogenetic hypothesis of evolutionary relationships within this and other flowering plant lineages based on RADseq data. This research revealed the existence of five clades of a core genus Stellaria, offered clarification of taxonomic boundaries of starworts, provided evidence for resurrection of two plant genera related to Stellaria (Adenonema and Mesostemma), and also provided evidence for description of two new plant genera, Nubelaria and Rabelera of Eurasia. Circumscription of core Stellaria allowed for addressing of downstream evolutionary hypotheses. Namely, a well-sampled phylogeny of Stellaria enabled the biogeographical history of starworts to be reconstructed as well as the history of petal evolution. Analyses revealed a Miocene origin of Stellaria likely in northeastern Eurasia with myriad dispersals and radiations across the world subsequently, and also suggested widespread habitat and climate lability in the genus. Data also revealed numerous, recurrent losses of petals in unrelated starwort lineages, and a field experiment on the alpine tundra of Niwot Ridge (Boulder County, Colorado) suggested that these losses may be associated with transitions from outcrossing to self-fertilizing pollination systems.</p
