by Étienne Léveillé-Bourret, Julian R. Starr
The circumscription of the circumboreal tribe Scirpeae has been contentious since the earliest infrafamilial classifications of the Cyperaceae (>100 genera, ~5,500 species). Molecular phylogenetic studies place Scirpeae in a strongly supported clade with the enigmatic genus Khaosokia and tribes Cariceae, Dulichieae, and Sumatroscirpeae, a lineage comprising more than 40% of all Cyperaceae species. This lineage was previously known as the Cariceae-Dulicheae-Scirpeae (“CDS”) clade. Here we informally characterise it as the “Scirpo-Caricoid Clade”. Previous phylogenetic and phylogenomic studies of the Scirpo-Caricoid Clade have shown Scirpeae to be paraphyletic, forming four distinct lineages that are successive sisters to a Cariceae + Sumatroscirpeae clade, thus confirming decade old suspicions that the modern circumscription of Scirpeae is unnatural. Using a total-evidence phylogenetic analysis incorporating three plastid markers (matK, ndhF, rps16), two nuclear ribosomal markers (ETS-1f, ITS), and 64 morphological characters, this study confirms the paraphyly of Scirpeae, the isolated phylogenetic position of Khaosokia, and identifies morphological synapomorphies for seven monophyletic lineages that are here recognized as tribes. Our new classification places for the first time all genera of the Scirpo-Caricoid Clade into natural tribes that are identifiable using morphological and embryological characters. Three new tribes are proposed: Calliscirpeae trib. nov., Khaosokieae trib. nov. and Trichophoreae trib. nov. Diagnoses for all tribes of the Scirpo-Caricoid Clade, an identification key to all currently recognized Cyperaceae tribes, and identification keys for all genera of the Scirpo-Caricoid Clade are provided.