Grateloupia tenuis Wang et Luan sp. nov. (Halymeniaceae, Rhodophyta): A New Species from South China Sea Based on Morphological Observation and rbcL Gene Sequences Analysis

Grateloupia tenuis Wang et Luan sp. nov. is a new species described from Lingshui, Hainan Province, South China Sea. Based on the external form and internal structure, combined with rbcL gene sequence analysis, Grateloupia tenuis is distinct from other Grateloupia species as follows: (1) thalli is slippery and cartilaginous in texture; possess fewer branches, relatively slight main axes, and two or three dichotomous branches; (2) cortex is 5-6 layers; medulla is solid when young, but hollow in old branches; reproductive structures are dispersed in main axes of thalli and lower portions of branchlets; exhibits Grateloupia-type auxiliary cell ampullae; (3) the four studied G. tenuis sequences were positioned in a large Grateloupia clade of Halymeniaceae, which included sister group generitype G. filicina with 68 bp differences; G. tenuis was determined to be a sister taxon to the G. catenata, G. ramosissima, G. orientalis, and G. filiformis subclade. The pairwise distances between G. tenuis and these species were 39 to 50 bp. The sequences of G. tenuis differed by 81–108 bp from the sequences of other samples in Grateloupia; there are 114–133 bp changes between G. tenuis and other genera of Halymeniaceae. In final analysis, we considered Grateloupia tenuis Wang et Luan sp. nov. to be a new species of genus Grateloupia.