Morphology, phytogeography, and systematics of the diatom genus <italic>Hannaea</italic> (Bacillariophyceae).

Abstract

The diatom genus <italic>Hannaea</italic> 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 <italic>Fragilaria</italic> and <italic>Synedra</italic>. Multiple lines of morphological, phytogeographical, and phylogenetic evidence were utilized to examine the diversity and relationships within <italic>Hannaea </italic> and among related taxa. First, morphological differences among <italic>Hannaea</italic> taxa were documented with light and scanning electron microscopy. Valve metrics (e.g., length, width, and curvature) from nine morphologically diverse <italic> Hannaea</italic> 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 <italic>Hannaea</italic>); these hypotheses examined the monophyly of <italic>Hannaea</italic>, the sister taxon of <italic> Hannaea</italic>, and overall relationships in Fragilariaceae. Geographic distributions showed that the genus <italic>Hannaea</italic> contains some taxa that are widespread but ecologically restricted (<italic> H. arcus</italic> and varieties) and endemic taxa (<italic>H. mongolica, H. superiorensis</italic>, and <italic>H. recta</italic>) restricted to regions or lake systems. Finally, the cladistic analysis shows <italic>Hannaea</italic> to be monophyletic in a clade with <italic>Fragilaria sensu stricto</italic> (making <italic>Fragilaria sensu stricto</italic> paraphyletic). The monophyly of <italic>Hannaea</italic>, based on a combination of characters in addition to an arcuate valve, supports the separation of <italic>Hannaea</italic> as a genus. Overall, results from the morphological, ecological, and cladistic analyses supported the description of two new taxa: <italic>Hannaea superiorensis</italic> sp. nov., an endemic species from the Great Lakes and <italic>H. mongolica </italic> sp. nov. from the Baikal Rift Zone. Additionally, <italic>Ceratoneis arcus</italic> var. <italic>recta</italic> will be transferred and elevated to <italic>H. recta</italic>, based on its limited geographical distribution, valve morphology and hypothesized evolutionary relationship within <italic> Hannaea</italic>. The two varieties of <italic>H. arcus, H. arcus</italic> var. <italic>amphioxys</italic> and <italic>H. arcus</italic> var. <italic> linearis</italic>, 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.