Cocconeis czarneckii sp. nov. (Bacillariophyta): a new diatom species from Lake Okoboji (Iowa, USA), based on the strain UTEX FD23

ABSTRACT

The nucleotide sequences (18S and rbcL) of the freshwater diatom strain UTEX FD23 were revisited and its morphology studied for the first time. This strain is maintained at the UTEX Culture Collection of Algae, where it is referred to as Cocconeis placentula var. lineata. The sequences of this strain had been deposited in NCBI and used in more than 30 studies mostly under the name C. placentula, but also C. placentula var. lineata. We describe this species as new, based on sequence data and morphology (LM and SEM), which did not correspond to the epitypes of C. placentula var. placentula, C. lineata or any other described member of the C. placentula group. According to genetic distances for 18SV4, this new species is closest to C. placentula sensu stricto (5.8%), and has a distance of 7.9% to C. lineata. For rbcL, C. czarneckii is closest to the recently described C. coreana (2.6%–2.8%), it has a distance of 4.1% to C. lineata, and of 4.2% to C. placentula. Morphologically, C. czarneckii shares similarities with C. sijunghoensis, C. amerieuglypta, C. klamathensis and C. grovei, which differ by valve size and outline, numbers and pattern of submarginal areolae, and ultrastructural details of the valvocopula of the raphe valve. Our study, integrating available nucleotide sequences with a detailed morphological characterization of the strain UTEX FD23, added to our understanding of the heterogeneity of the C. placentula group, and will benefit the scientific community interested in this strain (e.g. for taxonomy, molecular phylogenetics and eDNA metabarcoding).

KEYWORDS:

• Algae culture collections
• Freshwater biodiversity
• Genetic distance
• Micromorphology
• Type material

ACKNOWLEDGEMENTS

The authors acknowledge the assistance in Scanning Electron Microscopy by Dr. Ryan Nicholl and Eric Alvarez at the Nano3 Facility at the University of California, San Diego. We are grateful to Dr. Mark Edlund who provided relevant information on Dr. David Czarnecki and his living collection of diatoms. Thanks to the two anonymous reviewers and the editor (Dr. António José Calado) for their very helpful comments.

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the authors.

SUPPLEMENTARY MATERIAL

Supplemental data for this article can be accessed on the publisher’s website.

Additional information

Funding

The California State Water Resources Control Board Surface Water Ambient Monitoring Program provided funding for this study. The work of Demetrio Mora is supported by the project “Molecular Methods for Biodiversity and Ecological Assessment of the German Federal Waterways”, funded by the Federal Ministry of Transport and Digital Infrastructure (BMVI).