Species diversity and molecular phylogeny of Crustaphytum and Mesophyllum (Hapalidiales, Rhodophyta) from the Asian Pacific, including three new species of Crustaphytum

ABSTRACT The non-geniculate coralline algal genus Crustaphytum occurs in subtropical regions of the Pacific and Atlantic Oceans and presently contains only two species, C. pacificum and C. atlanticum. In contrast, the genus Mesophyllum is more widely reported and has representative species in both warm and cold waters. We analysed the species diversity of collections of Crustaphytum and Mesophyllum-like specimens from the Asian-Pacific region, based on psbA and rbcL sequence analyses and morphology. Our molecular analyses showed that the collections of Mesophyllum-like specimens mostly belonged to Crustaphytum with only a few specimens clustering with the Mesophyllum/Melyvonnea complex. We also describe three new species of Crustaphytum (C. taiwani-boreale sp. nov., C. taoyuanense sp. nov. and C. fragile sp. nov.) that are commonly found in the algal reefs in Northwest Taiwan, utilizing both scanning electron and light microscopy, and DNA sequence analyses. Crustaphytum fragile (79–95 μm thick) and Crustaphytum taiwani-boreale (235–436 μm thick) mostly grow in similar habitats in the algal reefs and can only be distinguished by a combination of characters relating to tetrasporangial chamber size and the number of cell layers in the cortex and medulla. Crustaphytum taoyuanense (233–300 μm thick) can be separated from the other species by its violet-red colour and by the margins of older thalli becoming overgrown by adjacent thalli. Crustaphytum taoyuanense and C. fragile are restricted to Taoyuan City in Northwestern Taiwan, whereas C. taiwani-boreale has a broader distribution in Northern Taiwan. Our study reveals a rich species diversity of Crustaphytum in the warm water region of the Western Pacific Ocean.