Cumathamnion serrulatum

Thallus blade-like, soft, mucous, to 12 cm long, pink-red to reddish-purple color. Blades lanceolate, thin (one cell thick), up to 0.8 cm wide and 10 cm long, with pointed apices, with distinct midrib and veinlets (first and second orders), abundantly alternately originating (from the left–from the right) from midrib of the parent blade. The midrib and veinlets composed of several cells thick. Branches leaf-like, of 3–4 orders. Margins of parent blades and prolifications finely toothed, undulate. Midribs of old blades after erosion of their leaf-like part turned into stalks. Spermatangial sori linear, develop on both surfaces of the branches along midrib. Cystocarps hemispherical, to 570 μm in diam. Attachment by discoid holdfast. Growing in the low intertidal and upper subtidal zones, on rocky with silt-covered sand and muddy-sandy bottom in protected coastal areas.

Common in countries of the Asia-Pacific Region.