A taxonomic and systematic revision of the genus Muelleria (Bacillariophyta)

The genus Muelleria (Frenguelli) Frenguelli is considered in taxonomic, systematic, and biogeographic contexts. Muelleria is a small genus composed of 15 known species. In the present report, four species are newly described (M. algida S.A. Spaulding et Kociolek sp. nov., M. luculenta S.A. Spaulding et Kociolek sp, nov., M. variolata S.A. Spaulding et Kociolek sp. nov., and M. varipunctata S.A. Spaulding et Kociolek sp. nov.) and illustrated in light microscopy and scanning electron microscopy. In addition, one new combination is made [M. holmenii (Foged) S.A. Spaulding et Keciolek comb, nov.] and three lectotypes are designated [M. linearis (O. Muller) Frenguelli, M. gibbula (Cleve) S.A. Spaulding et Stoermer, M. patagonica (O. Muller) Frenguelli]. The genus Muelleria has an unusual geographic distribution. Unlike other diatom genera, most of the species [except M. terrestris (Petersen) S.A. Spaulding et Stoermer and the cosmopolitan M. gibbula] are restricted to high latitudes of either the southern or northern hemisphere. The taxa are narrowly endemic, with species restricted to isolated habitats such as oceanic islands (Iceland, Kerguelen Island, and South Shetland Islands) and arid desert lakes (South Victorialand region of Antarctica and southern Argentina). A cladistic analysis is performed based on morphological characters for 11 Muelleria species and four outgroup taxa. The results of this analysis indicate that Muelleria is a monophyletic group, lending support to the resurrection of the genus and to the hypothesis that lineages, not just individual species, share restricted distributions. Among southern hemisphere species, one lineage of Muelleria is primarily South American and the second is primarily Antarctic.