Molecular phylogeny of the widespread <i>Martensia fragilis</i> complex (Delesseriaceae, Rhodophyta) from the Indo-Pacific region reveals three new species of <i>Martensia</i> from Taiwan

The genus Martensia is characterized primarily by its unique thallus morphology, wherein a proximal membranous blade is interrupted distally by one to several bands of net-like tissue (networks). Among the known species, M. fragilis is characterized by fan-shaped, membranous blades with multiple bands of networks. The species has been frequently reported from warm temperate and tropical regions. Collections from various localities in the Indo-Pacific region included many specimens fitting this broad concept of M. fragilis, but differed in several aspects and were difficult to assign to any named species with confidence. In order to delineate the species boundaries within this suite of M. fragilis-like specimens and to clarify the phylogenetic significance of the morphological features used for separating species of Martensia, we used analyses of rbcL sequence to infer phylogenetic relationships among the available species with multiple bands of networks. Molecular analyses revealed that M. fragilis was restricted to its type locality Sri Lanka and that collections of M. ‘fragilis’ from other regions were split into six clades. Martensia ‘fragilis’ collections from Taiwan contained three cryptic species, which were described as new species (M. leeii W.-C. Yang & S.-M. Lin sp. nov., M. kentingii W.-C. Yang & S.-M. Lin sp. nov. and M. taiwanifretensis W.-C. Yang & S.-M. Lin sp. nov.) based on molecular and morphological evidence. RbcL sequences of M. ‘fragilis’ from Korea and Japan, as well as those of the recently described M. bibarii and M. jejuensis, were all virtually identical, indicating that previous records of M. fragilis from those regions should go under the name M. jejuensis, with M. bibarii placed in synonymy. Records of M. ‘fragilis’ from other locations in the Indo-Pacific should be regarded as doubtful until detailed morphological studies and molecular analyses of freshly collected specimens become possible