New and interesting diatoms from Tibet. III. Valve ultrastructure of two Neidium Pfitzer species from Tibet: comparison with other morphological groups of Neidium and consideration of phylogenetic relationships within the genus

Abstract

We present light and scanning electron microscope observations on two Neidium species, N. didelta and N. rectum, described by Friedrich Hustedt from Tibet. Neidium didelta and N. rectum have external proximal raphe ends that are deflected in opposite directions, as well as the presence of lacinia and renilimbi, all features of most members of the genus. Both species have a unique combination of characters. Internally, they have coverings over the longitudinal canals and areolae that are pluriseriate, much like the situation in the genus Neidiomorpha, and unlike other Neidium taxa. The areolae at the valve margin are larger than the other areolae comprising the striae. We compare these species with taxa described by Zhu & Chen, and suggest that these taxa are later synonyms of Hustedt’s species. We discuss the possible systematic affinities of these taxa within the Neidium and Neidiomorpha lineage.

Keywords:

• scanning electron microscopy
• Neidium
• Tibet
• phylogenetic relationships
• morphology
• Neidiomorpha

Acknowledgements

We are grateful to Li Bo for help with the collection of samples in the field and Yu Pan for his help in acquiring SEM images. We appreciate the helpful comments of two anonymous reviewers. Dr Patrick Rioual provided specific location information for the collections studied by Hustedt and Zhu & Chen.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was funded by the National Nature Science Foundation [grant number 31970217], the One-hundred Talent Program of Shanxi Province and the Shanxi ‘1331 Project’ Key Innovative Research Team Program of Shanxi and the Fund for Shanxi ‘1331’ Project.