Orthoseira helvetica sp. nov. – a new diatom (Bacillariophyceae) from the Swiss Alps.

This paper describes a new diatom species (Orthoseira helvetica sp. nov.) found in the Swiss Alps at an elevation over 2600 m a.s.l. The diatom was recorded at the Macun plateau, Swiss National Park, from samples of terrestrial and wet semi-terrestrial mosses near the stream splash zone. The diatom has a unique set of features and is easily recognized under light and scanning electron microscopy. The most distinctive feature is the presence of a prominent silica collar in a 'rose flower' shape rounding each carinoportulae and an additional silica collar on the areolae (first 3–4 rows) bordering the hyaline area. The valve diameter of O. helvetica sp. nov. is 7.5–26.5 µm and possesses 2–3 (usually 3) carinoportulae. Linking spines at the valve face/mantle junction are present, having a simple basis and being triangular in shape. [ABSTRACT FROM AUTHOR]