Peyssonnelia rubra (Greville) J.Agardh 1851

    Crusts brownish red to dark red in colour, calcified, brittle, 80-250 µm thick, 2-6 cm in diameter, circular with an irregular margin, later the margins splits into cuneate to reniform lobes 12-14mm long. Thallus attached to the substratum by numerous unicellular rhizoids, entire crust adherent to the substratum and margins free; surface of thallus shows radial striae or concentric zone. Surface view of the thallus shows slightly radial or irregularly arranged marginal cells. Section of the thallus shows monostromatic hypothallium composed of elongated cells arranged parallel to radial, 24-42 µm long and 10-21 µm.

    Perithallium consists of six to ten cells high, obliquely ascendant; cells 8-27 µm wide, almost as long as broad in the lower part and progressively shorter in upper parts.