Morphology and phylogenetic position of three new raphid diatoms (Bacillariophyceae) from Hangang River, South Korea

Abstract

Epilithic diatoms were isolated and cultured during ecological investigations of the Hangang River, South Korea. Three species belonging to the genera Fragilaria, Nitzschia, and Encyonema were investigated using morphological and molecular data. Their morphological characteristics were analyzed using light microscopy (LM) and scanning electron microscopy (SEM). The nuclear small subunit (SSU) rRNA and ribulose-1, 5-bisphosphate carboxylase/oxygenase (rbcL) genes were used to study the molecular characteristics of these taxa. We herein describe three new species: 1) Fragilaria thornata, which has spatulate spines tapering towards their tips; 2) Nitzschia hantanense. which has a small-sized frustule with convex margins and parallel striae in the central part of the valve that become strongly radial towards the poles; 3) Encyonema equalis, which has a space between projections, located on the upper siliceous struts, that is consistent whether near the margin or near the raphe. According to the molecular analysis of three species, there also give a strong evidence to separate these three species as new species based on the phylogenetic tree and genetic distance of SSU rRNA and rbcL gene. The result of all analyses support that Fragilaria thornata, Nitzschia hantanense and Encyonema equalis are new to science.