New and interesting diatoms from the Shimen Wetwalls, Yunnan Province, China. I. Valve morphology of Melosira radiato-sinuata var. yunnanica Chen (Bacillariophyta: Melosirales) from Yunnan Province, China, with comments on its systematic position

We examine and describe the frustular morphology of the diatom originally described as Melosira radiato-sinuata var. yunnanica from a wet wall in Yunnan Province, China, based on light and scanning electron microscopy. This diatom has carinoportulae present in the central portion of the valve, and prominent caverns present internally around the periphery of the valves. The valve mantle height varies. Based on these features M. radiato-sinuata var. yunnanica is transferred to the genus Orthoseira and recognized as a distinct species. It is compared to other, similar 'centric' diatoms. Several other, similar taxa are also formally transferred to the genus Orthoseira, including M. radiato-sinuata, and Melosira undulata var. triocellata. 'Orthoseira sp. #2' sensu Spaulding and Kociolek is formally described as a new species. A discussion of the morphological diversity within the genus Orthoseira is presented.