A reassessment of Halophila species (Hydrocharitaceae) diversity with special reference to Japanese representatives

Abstract

In a recent review of the seagrass genus Halophila in Japan, eight taxa including four new species were listed: (i) H. decipiens, (ii) H. minor, (iii) H. major, (iv) H. ovalis, (v) H. mikii, (vi) H. nipponica, (vii) H. okinawensis, and (viii) H. gaudichaudii. In this study, the specific concept of Halophila in Japan as well as some other geographic areas was re-assessed by a combination of nuclear ribosomal ITS1, 5.8S rDNA, and ITS2 sequence analyses and morphological examinations of both recently collected materials and available type collections. The results confirm the distinctness of the Australian endemic species H. australis and the putative pan-tropical taxon H. decipiens; but also demonstrate conspecificity of: (i) H. minor and H. ovalis; (ii) H. major and H. mikii; and (iii) H. nipponica, H. okinawensis and H. gaudichaudii. As an outcome of this study, we recommend restricting the list of Halophila representatives in Japan to the following four species: (i) H. decipiens, (ii) H. major, (iii) H. ovalis, and (iv) H. nipponica. In addition, we predict the possibility of H. major occurring further south than currently recorded.

Is Halophila major (Zoll.) Miquel a big H. ovalis (R. Brown) J.D. Hooker? An evaluation based on age, morphology, and ITS sequence

“…major is reported to be distributed in Western Pacific region including Vietnam, Indonesia, Malaysia and the Indian Ocean including Thailand and Myanmar either through the morphological or molecular information 12,19,20 . This study was the first report, which combined both morphological features and molecular information to identify H. major and suggested some key characters to identify this closely similar species.…”

“…These observations reveal that the taxonomic status of the group is still unclear. Besides, molecular studies by Uchimura et al 12 revealed that H. major occurred in Thailand, which was the first record of H. major in Thailand. A recent report by Nguyen et al 20 suggested the occurrence of H. major in Thailand; however its morphological features had never been examined.…”

“…Although H. ovalis is widely distributed, it has been represented as a single collective species 1,9 . The five species of Halophila reported from Thailand are H. ovalis, H. beccarii, H. minor, H. decipiens, and H. major [10][11][12] . H. ovalis is also common in Thai waters, forming extensive beds along the Andaman coast.…”

“…Later however it was recognized as two distinct species 18 . H. ovata is now an illegitimate name and is proposed as H. gaudichaudii 19 ; but a recent study 12 suggested that H. gaudichaudii was a synonym of H. nipponica. These observations reveal that the taxonomic status of the group is still unclear.…”

“…Recent studies using var- ious genetic markers of plastid sequences have clarified the identification of the Halophila species 21,22 . Ribosomal internal transcribed spacer (ITS) sequences could be used to study and identify the genetic relation between Halophila closely related species 12,20,23,24 . It is unknown weather there is any difference in ITS molecular analysis between big and small leaf morphological forms of H. ovalis.…”