Two new Encyonema species from Europe compared to the type material of E. minutum and E. silesiacum (Gomphonemataceae, Bacillariophyceae)

ABSTRACT

Cymbella minuta Hilse and C. silesiaca Bleisch, transferred in 1990 to the genus Encyonema, are two species frequently observed in European rivers. The original material of both species was included in Rabenhorst’s historical exsiccata series (numbers 1261 & 1802) and illustrated by Kurt Krammer in 1997. Despite this publication, the morphological variability of these two species is poorly known, and interpretations of this variability are often too broad or not precise enough. Recently, several populations of Encyonema displaying intermediate morphological features between E. minutum and E. silesiacum have been observed in Europe, making a reliable identification of these taxa impossible. Based on the currently available literature, two taxa that could not be assigned to an existing species are described as new: E. morvanense and E. vandammeanum. The present paper illustrates and discusses the morphology of the type material of E. minutum and E. silesiacum and compares it with both new species. Encyonema morvanense is distinguished by its typically protracted, rostrate apices, a low length/width ratio, the presence of an isolated pore, and areolae that are discernible under LM. In contrast, E. vandammeanum also exhibits protracted apices, but a higher length/width ratio, areolae that are faintly discernible, and the absence of an isolated pore. Comparisons with other Encyonema species, described in 1997 by Krammer (such as E. brevicapitatum, E. minutiforme and E. simile), are added in order to better understand the differences and similarities between these species.

KEYWORDS:

• Encyonema
• new species
• Europe
• morphology
• type material analysis

Acknowledgements

The Service Public de Wallonie (SPW), Agriculture, Ressources naturelles et Environnement is thanked for permission to use sample BERW-03803 and providing the necessary physico-chemical data.

Disclosure statement

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

Author contributions

Bart Van de Vijver

Contribution: generation and analyses of LM and SEM materials, discussion of results, development, writing, revision and editing of the manuscript.

Valérie Peeters

Contribution: analyses of LM materials, discussion of results, revision and editing of the manuscript.

Katharina Wilfert

Contribution: analyses of LM materials, discussion of results, revision and editing of the manuscript.

Myriam de Haan

Contribution: analyses of SEM materials, discussion of results, revision and editing of the manuscript.

Additional information

Funding

Funding for this research was provided by Meise Botanic Garden.