Revision of Ardissoneaceae (Bacillariophyta, Mediophyceae) from Micronesian populations, with descriptions of two new genera, Ardissoneopsis and Grunowago , and new species in Ardissonea , Synedrosphenia and Climacosphenia .

was resurrected from in 1986 and was included as a genus by Round, Crawford and Mann ("The Diatoms") in its own Family and Order. They commented that there might be several genera involved since the type species of the genus possesses a double-walled structure and other taxa placed in have only a single-walled structure. Two other genera of "big sticks," and , were placed in their own Families and Orders but share many characters with Ardissoneaceae, especially growth from a bifacial annulus. Eighteen taxa (11 new species) from Micronesia were compared with the literature and remnant material from Grunow's Honduras sample to address the concepts of and Ardissoneaceae. Phylogenetic and morphological analyses showed three clades within sensu lato: emend. for the double-walled taxa, emend. and for single-walled taxa. New species include .; ., , , and .; , , and Transfers include . and . , seen for the first time in SEM in Grunow's material, is transferred to Three more genera have similar structure: , and , erected for and a lanceolate species, Morphological characters of in our region support separation of and and suggest additional species here and elsewhere. was not found but we clarify its characters based on the literature and distinguish from it. and a very long, slender , previously identified as , were present along with . Morphological and molecular phylogenetics strongly suggested that all these genera belong in one family and we propose to include them in the Ardissoneacae and to reinstate the Order Ardissoneales Round.