Grateloupia filicina

Thallus caespitose, cartilaginous, slippery, 5–10(–20) cm high, linear, compressed to subcylindrical, shortly stipitate, purplishred, dark purplish-brown to bluish-green. Main axis (1.5–2 to 4 mm broad) with numerous branches (1 mm broad and 3–10 cm long) tapering to base and apex. Branching multifarious, commonly marginally pinnate, bipinnate, sometimes proliferating from the face, or radially branched. Attachment by small disclike holdfast. Tetrasporangia imbedded in the cortical layer, cruciately divided, near to oval (18–20x35–40 μm), scattered over all the thallus. Cystocarps embedded in the cortex and reach far into the medullary tissue, partially prominent, to 180 μm in diam. Growing on the middle intertidal rocks, in the intertidal rocky pools.

Note: A source of agglutinin.

Worldwide: Europe. Atlantic, Indian and Pacific Oceans, from tropics to Antarctic and the subantarctic Islands.