Plate tectonics in the microscopy realm: Molecular insights into morphological variability of <i>Peridinium willei</i> (Peridiniales, Dinophyceae)

Abstract Freshwater Peridinium willei (Peridiniaceae) is globally distributed, but reports linking its morphologies with DNA sequence data remain scarce. The taxonomy of the species, and its infraspecific taxa, remain ambiguous due to the lack of DNA sequence data for the original and type material. Field material from the Czech Republic, Germany, Italy and Poland was collected to establish strains for morphological analysis using light and scanning electron microscopy. The rRNA complex of the unialgal cultures was partially sequenced, yielding 69 new GenBank entries. Based on the study of 70 newly established strains, P. willei exhibits great morphological and genetic diversity, with the latter encompassing not less than 11 ITS ribotypes. Deviations from the archetypical plate pattern (with the basic thecal formula 4′, 3a, 7′′, 5c, 5s, 5′′′, 2′′′′) included shifts, additions or absences of sutures, eventually leading to variations in the number of thecal plates. No correlation between morphological, biogeographic and/or molecular data was detected, indicating that P. willei (like other Peridiniaceae) exhibits a high degree of intraspecific variability. The two varieties P. willei var. sphaericum and P. willei var. stagnale are epitypified based on material from their type locality (Leszno, Poland), while material from Berlin serves as reference material of P. willei var. lineatum .