Re-examination of Cyclotella lacunarum Hustedt (Bacillariophyta) from lakes in the Pamir Mountains, western China, and description of two similar Lindavia taxa collected from Tajikistan and Nepal

Originally described from a sample collected in the Pamir Mountains at the end of the nineteenth century, Cyclotella lacunarum Hustedt is a centric diatom species that is not-well defined and seldom reported in the scientific literature. Our investigations revealed that the type locality of this taxon, now referred to as Lindavia lacunarum (Hustedt) Nakov et al., is actually in western China and not in Tajikistan, as wrongly assumed previously. Light microscope (LM) and scanning electron microscope (SEM) observations of the type material and of modern material collected at the type locality allowed us to emend the description of this species. Its most remarkable character is that it possesses central fultoportulae with only two satellite pores instead of three as generally reported for similar species of Lindavia. Lindavia lacunarum was then compared to two similar populations of Lindavia collected from high elevation lakes in Tajikistan and Nepal. These two populations were originally identified as Cyclotella/Lindavia lacunarum and represent the only reported occurrences of this taxon outside its type locality. The population from Tajikistan differs from L. lacunarum by having cells of smaller size, with an almost flat valve face and has been described as a new variety Lindavia lacunarum var. karakulensis var. nov. The Nepalese population is more clearly differentiated from L. lacunarum by having a different type of colliculate pattern in the central area and significantly lower density of central fultoportulae and is therefore described as a new species, Lindavia nepalensis sp. nov.