Taxonomy and species diversity of Padina (Dictyotales, Phaeophyceae) from the Indo-Pacific with the description of two new species

ABSTRACT

Taxonomy, species diversity, and geographical distribution of the marine brown algal genus Padina (Dictyotales, Phaeophyceae) from tropical South-East Asian waters were investigated through a combination of morphological and molecular analyses. The study presents a new schematic diagram showing a suite of morphological characters including thallus hairline structures that are useful for species delineation in the genus. This study also revealed two new species from Myanmar, P. gracilis sp. nov. and P. lata sp. nov. based on molecular and morphological data. P. gracilis is characterised by a 2-layered thallus, thin hairlines on both surfaces of the thallus at equal distances, non-indusiate reproductive sori distally very close to the hairlines on the inferior surface, and the presence of Vaughaniella stage. P. lata is characterized by a 2–4-layered tiny thallus, broad hairlines located only on the inferior thallus surface, non-indusiate reproductive sori abutting the hairlines on the inferior surface and irregularly spreading on the superior surface, and the presence of Vaughaniella stage. This study also revealed new distributional records for four Padina species: P. okinawaensis from Myanmar and P. fasciata, P. ryukyuana and P. terricolor from the Philippines. These findings point to elevated species diversity in central Indo-Pacific waters. This study confirmed that most of the Padina species in the Pacific regions are showing overlapping distribution across the regions, in contrast to species from the Indian Ocean, which tend to be confined to specific localities.

KEYWORDS:

• cox3
• Dictyotales
• geographical distribution
• molecular observation
• morphology
• Padina gracilis
• Padina lata
• rbcL
• species diversity

Acknowledgements

We are grateful for loans of type specimens from L, MICH and SAP. We are also indebted to the Royal Botanical Gardens Victoria (MEL) for providing the high-resolution image of the type specimen of Padina antillarum (= Zonaria antillarum) MEL 583382 and to the staff of MEL for their kind assistance.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary information

The following supplementary material is accessible via the Supplementary Content tab on the article’s online page at https://doi.org/10.1080/09670262.2021.1883742

Supplementary table S1. Collection information of specimens used in this study and their DDBJ/GenBank accession numbers.

Supplementary figure S1. Maximum likelihood rbcL phylogeny of the genus Padina; root (A) and crown (B) trees. Numbers at the nodes display bootstrap values (>50%) for ML (left) and posterior probabilities (>0.90) for BI (right). Asterisks represent 100% bootstrap values and 1.0 posterior probability. New species and sequences reported in this study are described in bold.

Supplementary figure S2. Maximum likelihood cox3 phylogeny of the genus Padina; root (A) and crown (B) trees. Numbers at the nodes display bootstrap values (>50%) for ML (left) and posterior probabilities (>0.90) for BI (right). Asterisks represent 100% bootstrap values and 1.0 posterior probability. New species and sequences reported in this study are described in bold.

Supplementary figures S3–S22. Morphology of P. okinawaensis and P. terricolor. S3–S13. Morphology of P. okinawaensis. S3. Habit of a tetrasporophyte (NNW259). S4. Transverse section of the middle portion of the thallus (NNW262). S5. Transverse section of the basal portion of the thallus, showing unequal thickness of cell layers (NNW262). S6. Superior thallus surface, showing thin hairlines (double arrowheads) and heavy calcification (NNW347). S7. Inferior thallus surface, showing relationship of the alternating hairlines (arrowheads, the inferior surface hairlines; double arrowheads, the superior surface hairlines) and tetrasporangial sori (black arrows) with additional sori below the hairline (white arrows) (NNW239). S8. The inferior thallus surface of male gametophyte, showing the alternating hairlines (arrowheads, inferior surface hairlines; double arrowheads, superior surface hairlines) and antheridial sori (arrows) (NNW349). S9. Detail of a broad hairline (arrowhead) and tetrasporangial sori on the inferior thallus surface (NNW284). S10. Detail of a broad line (arrowhead) with a thin red hairline at its upper end (white arrow) and antheridial sori (arrow) on the inferior thallus surface (NNW302). S11. Detail of the inferior surface hairline, showing a broad line (arrowhead) with a thin red hairline at its upper end (arrow) (NNW239). S12. Transverse section of a tetrasporangial sorus with an empty tetrasporangium (arrowhead) (NNW246). S13. Detail of surface view of a tetrasporangium (NNW246). S14–S22. Morphology of P. terricolor. S14. Habit of a tetrasporophyte (NNW580). S15. Basal portion of the thallus with a Vaughaniella stage (arrow) (NNW556). S16. Transverse section of the middle portion of the thallus (NNW554). S17. Superior thallus surface with thin hairlines (arrowheads) (NNW573). S18. Inferior thallus surface with the alternating hairlines (arrowheads, inferior surface hairlines; double arrowheads, superior surface hairlines) and tetrasporangial sori (arrows) (NNW574). S19. Inferior thallus surface of female gametophyte, showing relationships of the alternating hairlines (arrowhead, inferior surface hairline; double arrowhead, superior surface hairline) and oogonial sori (arrows) (NNW597). S20. Detail of a hairline (arrowhead) and an oogonial sorus (arrow) with indusium (double arrowhead) (NNW597). S21. Inferior surface of male gametophyte with the alternating hairlines (arrowhead, inferior surface hairlines; double arrowheads, superior surface hairlines) and antheridial sori (arrow) (NNW582). S22. Detail of an antheridial sorus (arrow) and an inferior surface hairline (arrowhead) (NNW582).

Figures S23–S38. Morphology of P. fasciata and P. ryukyuana. S23–S30. P. fasciata. S23. Habit showing the inferior thallus surface (CEB4). S24. Transverse section of the middle portion of the thallus (CEB4). S25. Longitudinal section of the marginal portion of the thallus (CEB4). S26. Inferior surface of the thallus, showing the arrangement of broad uncalcified hairlines (arrowheads) and thin uncalcified lines (arrows) (NNW578). S27. Detail of a superior surface hairline (arrowhead) surrounding with the cuticle layer (arrow) (NNW560). S28. Superior surface of the thallus, displaying the arrangement of thin uncalcified hairlines (double arrowheads) and uncalcified lines (arrows) (NNW560). S29. Inferior surface of a tetrasporophytic plant, showing the structure and arrangement of a broad inferior surface hairline (arrowhead) and tetrasporangial sori (arrows) (NNW560). S30. Detail of immature tetrasporangia (NNW560). S31–S38. P. ryukyuana. S31. Habit in situ. S32. Tetrasporophytes, showing superior thallus surface (right) and inferior thallus surface (left) with small groups of rhizoid-like hairs (arrows) (NNW621). S33. Transverse section of the basal portion of the thallus (NNW616). S34. Longitudinal section of the marginal portion of the thallus (NNW616). S35. Inferior surface of the thallus, showing the arrangement of alternating hairlines (arrowheads, inferior surface hairlines; double arrowheads, superior surface hairlines) with small groups of hairs (arrows) (CEB12). S36. Superior surface of the thallus with thin hairlines (double arrowheads) (CEB12). S37. Inferior surface of a tetrasporophyte, displaying the arrangement of hairlines (arrowheads) and tetrasporangial sori (arrows) with a persistent indusium (double arrowhead) (NNW620). S38. Transverse section showing obovate tetrasporangia (NNW620).

Appendix S1. Detailed morphological features of four newly recorded species, P. okinawaensis, P. terricolor, P. fasciata, and P. ryukyuana, of Myanmar and Philippines, together with the list of all examined specimens of each species in this study.

Author contributions

Ni-Ni-Win: Original concept, fieldwork and sample collections, molecular analyses and morphological observations, data analysis, writing and editing manuscript; Mya-Kyawt-Wai, fieldwork and sample collections; P.J.L. Geraldino, fieldwork, sample collection, and editing manuscript; L.M. Liao, editing manuscript; Chaw-Thiri P.P. Aye, fieldwork and sample collections; Ni Ni Mar, fieldwork and sample collections; T. Hanyuda, data analysis; H. Kawai, general concept and editing manuscript; M. Tokeshi, general concept and editing manuscript.