Figure 1.

Polysiphonia morrowii is a non‐native red alga along Brittany coasts and it forms extensive, dense, and conspicuous patches of individuals in the higher intertidal zones. P. morrowii is considered to be native from the North Pacific Ocean and it probably arrived in Europe by human activities. This species was recently identified in Brittany using molecular tools even though it was probably unnoticed for long time due to its morphological similarities with the relative autochthon species, P. stricta and P. atlantica.