Searching for the sister to sedges (Carex): Resolving relationships in the Cariceae-Dulichieae-Scirpeae clade (Cyperaceae)

Abstract

With approximately 2000 species, tribe Cariceae (Cyperaceae) comprises a morphologically distinctive cosmopolitan clade, with holocentric chromosomes (N=6 to 56), complex biogeographical patterns, and habitat diversity ranging from rainforests to deserts. Such a remarkable combination of characteristics should make Cariceae an ideal model for studying the evolution of biodiversity, although they also obscure their relationships in Cyperaceae, complicating attempts to identify the contributing factors to diversity of Cariceae. Recent molecular studies place Cariceae in a strongly supported clade consisting of tribes Dulichieae, Scirpeae s.s, and the enigmatic monotypic genus Khaosokia, although relationships in this clade are unresolved. Using the plastid genes matK and ndhF and a greatly improved taxonomic sampling covering 16 of 17 genera and 55% of the species outside Cariceae, our analyses firmly position Dulichieae and Khaosokia (79% and 85% bootstrap support) as successive sisters to a clade consisting of five major lineages (Calliscirpus, Trichophorum+Oreobolopsis+Cypringlea, Cariceae, Scirpus+Eriophorum, and Amphiscirpus+Phylloscirpus+Zameioscirpus), the first four of which receive good to strong support (>80% bootstrap support). Cariceae are sister to the Trichophorum clade, although topological tests cannot exclude either Calliscirpus or a Scirpus clade+Zameioscirpus clade as sister to the tribe. Trichophorum appears to be paraphyletic and Eriophorum is firmly nested in Scirpus. There appears to be a trend in the increase of chromosome numbers in Scirpus and Eriophorum and a trend in the reduction and proliferation of the inflorescence throughout the major Cariceae-Dulichieae-Scirpeae clades.