Pterosiphonia pennata is a small brownish-red seaweed up to 8 cm high, with a rigid texture. Erect thalli are flattened in one plane, with several short lateral branches and occasional long branches arranged on each side of the frond giving a triangular outline. Usually 1.5-2 mm wide and it is up to 6 mm wide when main axes are branched. It has regular alternate lateral branching on every second axial segment.

Source: Marlin