Polymorphism in Mastogloia (Bacillariophyceae) revisited

Abstract

Background and aims – Mastogloia grevillei has been shown to be a polymorphic diatom species, producing frustules with morphology of Mastogloia grevillei, frustules with morphology of M. danseyi, and more rarely, heteromorphic or Janus cells with one valve of each morphology. Methods – We investigated a wetland population from Iowa (USA) known to produce heteromorphic valves and the type material of Mastogloia grevillei and M. danseyi to clarify the nomenclature of this taxon. Key results – The polymorphic shift in stria construction and density between Mastogloia grevillei and M. danseyi occurs in populations sampled decades apart, among widely separated populations, within single genotypes, and independent of sexual reproduction. Combining our observations with observations of type material for Mastogloia grevillei and M. danseyi we propose that Mastogloia danseyi f. grevillei stat. nov. be recognized as an ecophenotype of the nominate Mastogloia danseyi, as the latter taxon has nomenclatural priority. We also provide lectotypes for both taxa. Conclusions – Variability in stria structure and density between the two taxa is discontinuous and represents a probable polyphenism for diatoms that is likely triggered by changing total dissolved solids, conductivity, and/or solutes.