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

The genus Muelleria (Frenguelli) Frenguelli is considered in taxonomic, sys tematic, 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., an d M. varipunctata S.A. Spaulding et Kociolek sp. nov.) and illustrated in l ight microscopy and scanning electron microscopy. In addition, one new comb ination 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) Fre nguelli]. The genus Muelleria has an unusual geographic distribution. Unlik e 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 Ar gentina). A cladistic analysis is performed based on morphological characte rs for 11 Muelleria species and four outgroup taxa. The results of this ana lysis indicate that Muelleria is a monophyletic group, lending support to t he resurrection of the genus and to the hypothesis that lineages, not just individual species, share restricted distributions. Among southern hemisphe re species, one lineage of Muelleria is primarily South American and the se cond is primarily Antarctic.