Abstract: A critical reassessment of the morphological features of two closely related red algal genera, Grateloupia C. Agardh and Sinotubimorpha W. X. Li & Z. F. Ding (Halymeniaceae), pointed out that members of the two genera had most morphological characteristics in common, including the Grateloupia type auxiliary cell ampullae. Sinotubimorpha hitherto was distinguished from Grateloupia by: (i) the hollow axis; (ii) the presence of secondary filaments in ampullae; (iii) 1- to 3-celled carpogonial branch; and (iv) the occasional production of 1- to 4-celled flanking filaments on carpogonium. However, when these features were re-examined among 37 Chinese species of genera described in Flora Algarum Marinarum Sinicarum and one newly reported species, Grateloupia orientalis, we found that it was difficult to draw a clear-cut distinction between the two genera based only on morphological differences. In rbcL sequence analysis, all the species of Sinotubimorpha with G. catenata formed a single monophyletic subclade within the large Grateloupia clade of the Halymeniaceae. It is therefore suggested that all the Chinese species of Sinotubimorpha, S. catenata, S. guangdongensis, S. qingdaoensis, S. claviformis, and S. ramosissima should be synonymous with G. catenata, and that Sinotubimorpha should be included in synonymy under Grateloupia.

Key words: Grateloupia, Halymeniaceae, molecular phylogeny, morphology, rbcL, Rhodophyta, Sinotubimorpha, taxonomy.