Finding the sister to sedges (Carex): a new tribal and generic classification for the Cariceae-Dulichieae-Scirpeae Clade (Cyperaceae)

JULIAN R. STARR; SABINA DONADÍO; ANH TÀI VU; DANIEL SPALINK; KENNETH J. SYTSMA; BRUCE A. FORD; ROBERT F. C. NACZI; BING-HUA CHEN; EMILY MORIARTY LEMMON; ÉTIENNE LÉVEILLÉ-BOURRET; CLAIRE N. GILMOUR; THI KIM THAN NGUYEN; XIAO-FENG JIN; ALAN R. LEMMON

Rochester, Minnesota

Conferencia; Botany 2018 - Thriving with Diversity; 2018

Botanical Society of America (BSA), American Society of Plant Taxonomists (ASPT), Canadian Botanical Association/L'Association Botanique du Canada (CBA/ABC), International Association for Plant Taxonomy (IAPT), American Fern Society (AFS), y otras.

For over a century, the origins and mechanisms underlying the diversification of the enormous temperate genus Carex (>2000 species; Cariceae, Cyperaceae) have remained largely speculative. Characteristics such as its diverse ecology, varied biogeography, and intriguing cytology have made Carex a powerful model for studying plant evolution, but uncertain sister-group relationships hinder its use in studies that depend on accurate ancestral state estimates and biogeographic inferences. Over the past five years, we have focused our research on resolving relationships within the major clade to which Carexbelongs, the Cariceae-Dulichieae-Scirpeae (CDS) clade, a lineage containing 18 genera and approximately 40% of all Cyperaceae species (~2,100). Although initial phylogenetic studies based on nuclear and plastid Sanger-sequence markers suggested that Carex was nested within a paraphyletic tribe Scirpeae, and that several Scirpeae genera could also be paraphyletic, backbone nodes were unsupported. This meant the sister-group to Carex could not be determined, and any reclassification of CDS would be problematic. Using a subset of key taxa, we generated data for 461 nuclear exons using a universal flowering plant Anchored Phylogenomics probe set. These phylogenomic analyses were fully congruent with previous Sanger-based phylogenies, but they resolved all backbone nodes with high support, corroborating the need for a new tribal and generic-level revision of CDS. Although phylogenomic trees firmly place the Trichophorum Clade (Trichophorum, Oreobolopsis, Cypringlea) as sister to Carex, long branches and considerable morphologically differences emphasized the isolated position of Carex. This highlighted the importance of sampling Sumatroscirpus, the only CDS genus never before included in molecular analyses. Although rarely collected and believed to be a monospecific Sumatran endemic, taxonomic revision revealed that Sumatroscirpus consists of four species distributed north to China, including a locality in northern Vietnam where DNA could be obtained. Molecular analyses positioned Sumatroscirpus as sister to Carex, a relationship supported by a morphological synapomorphy: sheathing spikelet prophylls (perigynia). Moreover, it supported previous hypotheses suggesting an important role for Southeast Asia in the historical biogeography of Carex. With all CDS genera now placed in a robust phylogenetic framework, it is finally possible to propose a natural tribal classification for CDS. Combined molecular, morphological, anatomical and embryological data supports the recognition of seven tribes, four of which are new (Calliscirpeae, Khaosokieae, Sumatroscirpeae, Trichophoreae). Ongoing species-level studies of Trichophoreae and Scirpus, based on plastid, nuclear, RADseq, and morphological datasets will soon resolve the only remaining problems for generic circumscription in CDS.