Polysiphonia fibrata is a species of Polysiphonia that grows as small dense tufted and finely branched marine alga in the Rhodophyta.

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.

[1] Common around Britain including Shetland and Ireland.

[2] Other species are similar to P. fibrata and difficult to distinguish.