Four new Orthoseira Thwaites species from Maui, Hawaii, and the Columbia River Gorge, Oregon, with comments on frustular morphology in the genus

Light, scanning electron and focused ion beam microscope observations are presented for four new species of the diatom genus Orthoseira Thwaites. Three species, O. mauiana sp. nov., O. loweana sp. nov. and O. hawaiiensis are described from Maui (Hawaiian Islands), and one species, O. oregoniana sp. nov., is described from Oregon, USA. These four species all possess carinoportulae, the feature that diagnoses the genus, but differ in many other characters, including presence and types of spines, caverns, and pore fields. We compare and contrast these species with each other, and other species currently assigned to the genus. We also compare the different morphologies with other genera proposed, but not currently recognized, such as Liparogyra Ehrenberg, Stephanosira Ehrenberg, and Porocyclia Ehrenberg, and consider the systematic relationships of these groups within Orthoseira.