Polysiphonia elongata is a small red marine algae in the Rhodophyta.

The final branches are pointed at the apex and attenuate at their base.

[2] P. elongata grows intertidally and sublittorally on rock,[3] stones and artificial material also on other algae.

Spermatangial branchlets are borne near the apices of young branches.

Tetraspores occur in spiral series in the upper branches.