Halymenia dilatata Zanardini 1851

    Thallus erect, rose, dark red to reddish brown colour, and surface highly mucilaginous, 20-72 cm high. Thallus with small basal attaching disc, the single or occasionally two, rarely more stipitate erect fronds. Stipe very short, horny and sub-terete expanding abruptly into the broad lamina; Lamina as long as broad, variable in shape, ranging from flabelliform to oblong, entire or palmatifid, the lobes often imbricate; lamina margin with numerous small denticulate proliferations and frilled in appearance. Lamina surface usually maculate, the patches irregular and soriform; occasionally a few large proliferations, similar to the main blade, also present. Thallus 100 – 200 µm thick; Medulla large, composed of transverse medullary filaments, 6 – 10 µm broad, intermingled with the stellate cells and rhizoids; Stellate cells 25 – 36 µm diameter with arms up to 150 µm long. Rhizoidal cells 2 – 4 µm width and thick walled; Cortex narrow, few layered, the inner cells larger and gradually decreasing towards the margin, irregular to sub-stellate, 15-23 x 30-45 µm. Peripheral layer cells spherical, 5-9 µm diameter. Tetrasporangia cruciate, scattered over the surface of the thallus, ovoid to subspherical, 25-30 µm diameter.