Among angiosperms, sedges (Cyperaceae Juss., ca. 6,000 species worldwide) are notorious for their taxonomic difficulty. The largest named clade within the family is the tribe Cariceae, made up of the genus Carex and four embedded genera (Cymophyllus, Kobresia, Schoenoxiphium, and Uncinia; [1, 33, 52, 53]), for a total of ca. 2,000 species worldwide. Phylogenetic studies make clear that Carex is paraphyletic with respect to the other genera of Cariceae, and the global Cariceae research community has reached a consensus that these genera should be included within an expanded Carex (Cariceae Phylogeny Group., in prep.; Carex Biodiversity Synthesis Group, Encyclopedia of Life, Chicago, IL, September 26-30, 2011). For convenience, we often use Carex in the broad sense to refer to the Cariceae as a whole.
Carex species are ecologically important in habitats that range from tundra and dry sand prairies to open wetlands and bottomland forests and comprise the largest component of plant biodiversity of any angiosperm genus in a wide range of northern temperate habitats. Species discovery in the genus has continued almost unabated since the early 19th Century (Fig. 1). Much of the newly discovered diversity comes from recent work in China, where many records from even the past decade are jeopardized by development (pers. obs.). The high diversity of Carex in China, where the high degree of endemism is combined with substantial development pressure, highlights the urgency of this study. Categorizing, studying, and conserving this substantial component of plant biodiversity demands a global, comprehensive study of Carex biodiversity.
In a massive genus like Carex, infrageneric classification plays a crucial role in students’ ability to learn the genus. Sectional Carex classification in temperate floras allows field practitioners to efficiently navigate this genus, which includes numerous habitat specialists and dominants of many threatened ecological zones. Moreover, researchers depend on the sectional classification to identify taxa for phylogenetic and revisionary study. Carex is an excellent system for understanding patterns and processes of species diversification and trait macroevolution. Such studies depend on having delineated clades to investigate. As it currently stands, most studies in Carex require broad sampling outside of the section of interest to assess monophyly, diluting the effort to understand patterns within the lineage in question.
Despite the importance of infrageneric classification in Carex, sectional classification in various parts of the globe have developed largely independently from 1909 until the 2000’s. This has led to varying and confusing circumscription of sections and application of sectional names. The past decade has seen a few significant efforts to summarize sectional circumscription for substantial portions of the genus, as well as substantial insight into the overarching phylogenetic structure of the genus. However, we are still without a phylogenetic sectional classification for the genus. In our 2011 synthesis meeting, we found that coming up with a “state of the art” classification that would work worldwide was nearly impossible given the data at hand (http://tinyurl.com/CariceaeSampling). Developing a predictive classification, one that will guide future research, requires an integrated, international phylogenetic revisionary effort.