A morphological investigation of Neidium temperei Reimer (Bacillariophyta), and a consideration of its systematic placement

Abstract

Species previously assigned to the genus Neidium Pfitzer have recently undergone some revision, with the creation of a new genus Neidiomorpha Lange-Bertalot & Cantonati in Cantonati et al. [Cantonati M., Lange-Bertalot H. & Angeli N. 2010. Neidiomorpha gen. nov. (Bacillariophyta): A new freshwater diatom genus separated from Neidium Pfitzer. Botanical Studies 51: 195–202]. One species currently in Neidium is N. temperei Reimer (Reimer C.W. 1959. The diatom genus Neidium. I. New species, new records, and taxonomic revisions. Proceedings of the Academy of Natural Sciences of Philadelphia 111: 1–36), which is of interest because it shares important morphological characteristics with both genera. We present light and scanning electron micrographs of this species from populations in northern Michigan. The most notable characteristic shared between N. temperei and Neidiomorpha is that the external proximal raphe ends are not oppositely deflected. However, N. temperei shares other characteristics that differentiate Neidium from Neidiomorpha, including the presence of renilimbi around areolae on the internal valve surface, lacinia covering the external distal raphe ends and the structure of the longitudinal canals. A phylogenetic analysis of the relationships of these taxa and several additional species of Neidium with straight external proximal raphe ends suggests that Neidiomorpha is not monophyletic, there is a continuum of taxa between Neidiomorpha and Neidium, and due to a recent emendation of Neidium, several new genera will need to be described. The taxonomic implications of the phylogenetic analysis are explored, in the light of a recent emendation of the genus Neidium.

Keywords:

• Neidium
• Neidiomorpha
• diatoms
• Bacillariophyta
• northern Michigan
• ultrastructure
• morphology
• renilimbi
• systematics
• cladistics

Acknowledgements

The authors would like to thank Carrie Graeff for her expertise with the FESEM and the University Michigan Biological Station and the J.B. & Marilyn McKenzie Graduate Student Fund for funding the collection trip in summer 2012. Two reviewers, and the Associate Editor, offered constructive reviews and suggestions that have improved the manuscript.