Molecular systematics of targeted flat sedges (Cyperus, Cyperaceae) of the Americas

Background and aims – Cyperus is a large, ecologically diverse, and important sedge genus. Recent systematic work resolved problems with generic delimitation and implicated C₄ photosynthesis as a possible key innovation spurring diversification. Our research addressed several systematic, taxonomic, and biogeographic questions at the levels of species, species groups, and taxonomic sections. By targeting American taxa, this work helped fill a geographic sampling gap.

Methods – Phylogenetic relationships of 121 ingroup samples representing 93 taxa were inferred using both Bayesian and maximum likelihood approaches in a multi-locus framework with nucleotide data from nuclear ITS, and plastid markers matK, ndhF, rpl32-trnL^(UAG) , and trnH-psbA.

Key results – This study was the first to estimate the phylogenetic position of Karinia, a monotypic genus endemic to Mexico with a varied taxonomic history. Karinia mexicana is herein transferred to Scirpoides based on its phylogenetic position and morphology. Cyperus seslerioides and C. andinus, members of "section Dichostylis", belong in the C3 section Leucocephali. Previous work resolving Leucocephali as sister to C₄ Cyperus was corroborated. Molecular evidence provided taxonomic insight in some focal taxa but was inconclusive in others. Results support an amphitropical disjunction within the Cyperus rigens group, centred in subtropical South America, accounting for the presence of C. cephalanthus in southeastern North America where it is of conservation concern. An emerging biogeographic pattern is that many North American endemic C₄ Cyperus are derived from Mesoamerican ancestors.

Conclusions – Phylogenetic analyses with greater taxon sampling may solidify taxonomic decisions receiving preliminary support from this research. Loci with greater phylogenetic signal are required to resolve the Cyperus retrorsus and C. rigens complexes. Further testing of the integrity of section Leucocephali should be of high priority considering its compelling morphology and inferred relationship to C₄ Cyperus. This study builds on previous work with novel taxon and increased locus sampling and contributes to ongoing efforts to build a comprehensive phylogeny of Cyperus.