Polysiphonia fibrata
Polysiphonia fibrata is a species of "Polysiphonia" that grows as small dense tufted and finely branched marine alga in the Rhodophyta. Description. The branches of "P. fibrate" are numerous and much interwoven forming tufts up to 20 cm long. They are fine, terete, cylindrical, erect and dull brownish-red in colour. The branches consist of a central axis with 4 pericentral cells all of the same length as the axial cells. The branches become corticated near the base. Rhizoids and trichoblasts are abundant. Reproduction. The plants are dioecious. Spermatangia are borne near the tips of the branches. The  cystocarps are clearly shortly stalked. Tetrasporangia are formed in the branches near the tips. Habitat. To be found on rock, limpets, mussels and on other algae in rock pools at mid-tide and low water. Distribution. Common around Britain including Shetland and Ireland. Also recorded from Spain, and France. Note. Other species are similar to "P. fibrata" and difficult to distinguish.