Pterothamnion plumula (J.Ellis) Nägeli
Also commonly known as Antithamnion plumula (J.Ellis) Thuret; Bushy Feather Weed
Description: Thallus forming flaccid, purplish red tufts out of water 3-15 cm in length. Upright thalli branched in one plane, axes 1-3 mm wide. Thallus organisation very regular with the main axis giving rise to pairs of oppositely branched "whorl branchlets" (occasionally a further pair is formed at right angles to first pair).
Habitat: on rocks and stones in the lower intertidal and shallow subtidal to 20 m; widely distributed, common.
Photographs: Cornwall © David Fenwick