Pseudendoclonium commune Darienko et Proschold 2017, sp. nov.

Diagnosis: Plants on liquid SWES medium up to 1 mm consist of prostrate and erected filaments. The system of prostrate filaments is very dense and formed from packages or pluriseriate filaments. The vegetative cells of prostrate system are rounded, 6.4–10.4 μm in diameter, with a thick cell wall. The erect system is formed from short filaments, consisting of a maximum of 20 cells. The cells are cylindrical (10.8 × 5.4 μm till 16.5 × 5.4 μm) and generally 2–3 times longer than broad. The end cells are 8.0 × 3.2 μm till 12.0 × 3.2 μm. Branching is mostly unilateral, but sometimes it is also bilateral. Cells are uninucleate. The chloroplast is parietal, usually filling the cell, with a pyrenoid. Zoospores are not observed.

The species differs from other members of the genus by SSU-ITS sequences.

Habitat: Photobiont, on coastal rocks (Pelvetia -zone).

Type locality: Wales, Anglesey (Ynys Mon), Aberfraw.

Holotype (designated herein): The authentic strain SAG 2051 is permanently cryopreserved in metabolically inactive state (cryopreserved in liquid nitrogen) in the SAG, University of Göttingen, Germany.

Iconotype (designated herein in support of the holotype): Fig. 6 in this study.

ITS-2 DNA Barcode: PSE 4 in Figs S2.

Comment: This species is probably widely distributed as photobiont and free-living.Additional strains: SAG 2236 - photobiont of Verrucaria maura, Öland, Sweden; ULVO-21 - free-living biofilm on coastal rock (3 m high), Snake Island, Black Sea, Ukraine; ULVO-62 - free-living biofilm on concrete block in the tidal zone on Oakland beach, RI, USA.