Confirmation of Neoporphyra cf. dentata on Shikinejima, Izu Islands, southcentral Japan, and comparison with co-occurring Neoporphyra haitanensis

The Izu Islands of southcentral Japan are thought to fall within the distribution range of Neoporphyra dentata. However, the gametophytic blades of Bangiales collected from Shikinejima and Hachijojima, Izu Islands, were identified as Neoporphyra haitanensis in our previous study. Thus, it became uncertain whether N. dentata is distributed in the Izu Islands, including Shikinejima. To clarify whether N. dentata grows on Shikinejima, we conducted a further distribution survey of N. dentata on the island. The morphological features of the blade samples collected from an additional sampling site on Shikinejima were more similar to those of N. dentata than to those of N. haitanensis: the blade thickness and the division formula of spermatangia resembled those of the former species rather than the latter species. However, the division formula of zygotosporangia was different from those of either species. The phylogenetic analyses of the rbcL gene indicated that the samples were resolved in a clade including N. dentata collected from Shirahama, Chiba Prefecture, and Enoshima, Kanagawa Prefecture, Honshu, Japan. The p-distances of the chloroplast rbcL gene and nuclear 18S rRNA also supported identification of the samples as N. dentata. The results demonstrated that N. dentata is also distributed on Shikinejima with co-occurring N. haitanensis, and that the island materials of the two species are genetically different from other materials of the two species, respectively.

Automated summary

Our study found that the collected samples from Shikinejima and Hachijojima islands in the Izu Islands belong to Neoporphyra haitanensis, not Neoporphyra dentata as previously thought. To clarify the distribution of N. dentata on Shikinejima, we conducted further surveys and found that it co-occurs with N. haitanensis. Genetic analysis confirmed the differences between the two species.