Making 'Carex' monophyletic (Cyperaceae, tribe Cariceae): a new broader circumscription

Abstract

'Carex' (Cyperaceae), with an estimated 2000 species, nearly cosmopolitan distribution and broad range of habitats, is one of the largest angiosperm genera and the largest in the temperate zone. In this article, we provide argument and evidence for a broader circumscription of 'Carex' to add all species currently classified in 'Cymophyllus' (monotypic), 'Kobresia' (c. 60 species), 'Schoenoxiphium' (c. 15 species) and 'Uncinia' (c. 70 species) to those currently classified as 'Carex'. 'Carex' and these genera comprise tribe Cariceae (subfamily Cyperoideae, Cyperaceae) and form a wellsupported monophyletic group in all molecular phylogenetic studies to date. 'Carex' as defined here in the broad sense currently comprises at least four clades. Three are strongly supported ('Siderostictae', core 'Vignea' and core 'Carex'), whereas the caricoid clade, which includes all the segregate genera, receives only weak to moderate support. The caricoid clade is most commonly split into two clades, one including a monophyletic Schoenoxiphium and two small clades of species of 'Carex s.s.', and the other comprising 'Kobresia', 'Uncinia' and mostly unispicate species of 'Carex s.s.' Morphological variation is high in all but the 'Vignea' clade, making it extremely difficult to define consistent synapomorphies for most clades. However, 'Carex s.l.' as newly circumscribed here is clearly differentiated from the sister groups in tribe Scirpeae by the transition from bisexual flowers with a bristle perianth in the sister group to unisexual flowers without a perianth in 'Carex'. The naked female flowers of 'Carex s.l.' are at least partially enclosed in a flask-shaped prophyll, termed a perigynium. 'Carex s.s.' is not only by far the largest genus in the group, but also the earliest published name. As a result, only 72 new combinations and 58 replacement names are required to treat all of tribe Cariceae as a single genus 'Carex'. We present the required transfers here, with synonymy, and we argue that this broader monophyletic circumscription of 'Carex' reflects the close evolutionary relationships in the group and serves the goal of nomenclatural stability better than other possible treatments.