Toward an accurate taxonomic interpretation of Carex fossil fruits (Cyperaceae): a case study in section Phacocystis in the Western Palearctic.

Premise Of The Study: Despite growing interest in the systematics and evolution of the hyperdiverse genus Carex, few studies have focused on its evolution using an absolute time framework. This is partly due to the limited knowledge of the fossil record. However, Carex fruits are not rare in certain sediments. We analyzed carpological features of modern materials from Carex sect. Phacocystis to characterize the fossil record taxonomically.

Methods: We studied 374 achenes from modern materials (18 extant species), as well as representatives from related groups, to establish the main traits within and among species. We also studied 99 achenes from sediments of living populations to assess their modification process after decay. Additionally, we characterized 145 fossil achenes from 10 different locations (from 4-0.02 mya), whose taxonomic assignment we discuss.

Key Results: Five main characters were identified for establishing morphological groups of species (epidermis morphology, achene-utricle attachment, achene base, style robustness, and pericarp section). Eleven additional characters allowed the discrimination at species level of most of the taxa. Fossil samples were assigned to two extant species and one unknown, possibly extinct species.

Conclusions: The analysis of fruit characters allows the distinction of groups, even up to species level. Carpology is revealed as an accurate tool in Carex paleotaxonomy, which could allow the characterization of Carex fossil fruits and assign them to subgeneric or sectional categories, or to certain species. Our conclusions could be crucial for including a temporal framework in the study of the evolution of Carex.