Background:

Cyperaceae, with about 5,500 species and 90 genera worldwide, are the third largest family among Monocots. A unique combination of morphological and karyotypical features, among which stand holokinetic chromosomes, favors a rapid evolution and diversification and a high level of endemism in some groups. Preliminary checklists of Mexican sedges have been published but an updating of the taxonomy and nomenclature of the group for the country is required.

Questions:

How many and which species and genera of Cyperaceae are in Mexico?, what patterns of geographic distribution display those species?, which are the main gaps in the systematic knowledge in the family?

Study site and years of study:

Mexico, 1990 to 2016.

Methods:

A database of Mexican Cyperaceae was generated with basis in literature review, study of herbarium specimens (11 herbaria in Mexico and the United States) and field work, the last mainly focused on Carex. Diversity and endemism level were calculated. Besides, we analyzed in different space scales their distributional range.

Results:

Our dataset includes 460 species and 20 infraspecific taxa in 21 genera that belong to 10 of the 17 tribes of the family. Subfamily Cyperoideae includes almost 100 % of the Mexican sedges, as only one representative of subfamily Mapanioideae is known for the country. At the generic level, a drastic reduction in number (21) in comparison to previous inventories (27) results of recent phylogenetic and taxonomic rearrangements. The most diverse genera are Carex (138 taxa) and Cyperus (125), followed by Rhynchospora (65) and Eleocharis (57). Sedges in Mexico are found from sea level to above 4,300 m, in all types of vegetation. The highest diversity was found for Chiapas (237 taxa, 52 % of the total) and Veracruz (206 taxa, 45 %), followed by Oaxaca and Jalisco. Two genera (Cypringlea and Karinia) and 111 species or infraspecific taxa are endemic to Mexico (24 %), 43 of them micro-endemic (only known from one state in the country). Endemism increases to 57 % when the biogeographic extension known as Megamexico is included. Forty six names are excluded from the Mexican flora.

Conclusions:

Regardless of the addition of taxa and refining of the databases, the checklist presented here is still preliminary. Collection deficiencies and insufficient taxonomic revision for Mexican sedges are reflected in gaps in their knowledge. There are at least 45 undescribed species; including them the richness of Mexican sedges would exceed 500 species. Many complexes of species are in need of taxonomic revision, mainly in Carex but also in Bulbostylis, Cyperus, Eleocharis, Rhynchospora and Scleria. To advance in the inventory and better understanding of the diversity of Mexican Cyperaceae, we propose some research topics to be addressed in the short term.

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