Three species of Ulnaria (Bacillariophyceae) from China, with reference to the valve central area and apices

Abstract

Three needle-shaped Ulnaria species are studied using light and scanning electron microscopy. One is identified as Ulnaria acus (Kützing) Aboal and two are proposed as new: Ulnaria rhombus sp. nov. and Ulnaria wulingensis sp. nov. These three species have many common characters: needle-shaped valve outline, ghost striae, a central area circumscribed by shortened striae composed of one or a few areolae, a closing plate composed of a solid plate with some struts connecting the areola wall, and characteristic virgae-vimines structure. Ulnaria acus and U. wulingensis have almost parallel central area margins whereas U. rhombus never has parallel central area margins. Ulnaria wulingensis and U. rhombus (excluding few very small specimens) possess distinctive parallel distal regions of variable length, between 3 and 40 µm, but U. acus only has parallel distal regions in a few, very long specimens. Comparison with similar Ulnaria taxa was carried out and the distinguishing characteristics are summarized. All three species were found in alkaline freshwater (pH 8.3–8.5) with low-moderate conductivity (109.2–286.4 µS/cm).

Keywords:

• Closed valvocopula
• Dongting Lake
• parallel distal region
• new diatom species
• Wuling Mountains

Acknowledgments

We are grateful to Mr Xin Yang of Huaihua University for help with SEM operation and photography, to Xiaoyan Jiang, Jingjing Xu, Yongda Ou and Su Li for assistance in the field, and to two anonymous reviewers and the editor for their careful revisions and constructive comments.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research was supported by the National Natural Science Foundation of China (No. 31760051), the Natural Science Foundation of Hunan Province (No. 2018JJ2311).