| The diatom genus Hannaea is unique in its valve morphology and restricted ecological preferences. This araphid genus has been separated taxonomically by its arcuate valve outline but appears to be closely related to Fragilaria and Synedra. Multiple lines of morphological, phytogeographical, and phylogenetic evidence were utilized to examine the diversity and relationships within Hannaea and among related taxa.; First, morphological differences among Hannaea taxa were documented with light and scanning electron microscopy. Valve metrics (e.g., length, width, and curvature) from nine morphologically diverse Hannaea populations were used to separate or group these populations using multivariate statistics. Secondly, ecological preferences and geographical distributions also were compiled from collections and published records. Finally, cladistic analysis tested hypotheses of evolutionary relationships in the family Fragilariaceae (including Hannaea); these hypotheses examined the monophyly of Hannaea, the sister taxon of Hannaea, and overall relationships in Fragilariaceae.; Geographic distributions showed that the genus Hannaea contains some taxa that are widespread but ecologically restricted ( H. arcus and varieties) and endemic taxa (H. mongolica, H. superiorensis, and H. recta) restricted to regions or lake systems. Finally, the cladistic analysis shows Hannaea to be monophyletic in a clade with Fragilaria sensu stricto (making Fragilaria sensu stricto paraphyletic). The monophyly of Hannaea, based on a combination of characters in addition to an arcuate valve, supports the separation of Hannaea as a genus.; Overall, results from the morphological, ecological, and cladistic analyses supported the description of two new taxa: Hannaea superiorensis sp. nov., an endemic species from the Great Lakes and H. mongolica sp. nov. from the Baikal Rift Zone. Additionally, Ceratoneis arcus var. recta will be transferred and elevated to H. recta, based on its limited geographical distribution, valve morphology and hypothesized evolutionary relationship within Hannaea. The two varieties of H. arcus, H. arcus var. amphioxys and H. arcus var. linearis, remain at their current taxonomic status, based on morphological similarity and ecological overlap with the nominate variety. Formal descriptions and transfers will be done later in an effective publication. |
