Halymenia porphyriformis P.G.Parkinson

Scientific Description

Habit and structure. Thallus erect, foliose, pale red, with 1–several blades arising from a discoid holdfast. Blades with a short stipe to 2 mm long, or seemingly astipitate and arising directly from the holdfast, irregularly circular to elliptical, to 24 cm long, 22 cm wide and 200–500 µm thick, with a smooth surface with rare proliferations, and a soft texture. Blade margins smooth, undulate. Structure with filamentous medullary cells 4–6 µm diam., these mostly anticlinally arranged and traversing the blade from cortex to cortex, mixed with dark-staining ganglionic cells with a central core 12–30 µm diam. and numerous radiating arms 3–7 µm diam. Immature cortex with only 2 or 3 pigmented layers, the outer layer of subspherical cells. Cortex with 4–6 cell layers; inner layers of stellate cells with numerous secondary connections; outer layers of anticlinal di- or trichotomously divided filaments; superficial cells ellipsoidal, 7–12 µm long, 2–4 µm diam. [L:B 2–3 (–4)].

Reproduction. Spermatangia in sori on the thallus surface, solitary or in pairs on outer cells, subspherical, 2–3 µm diam. Other reproductive structures not seen.

Distribution. Known from Kenya, Pakistan, India, Sri Lanka, the Philippines, Fiji and Papua New Guinea, and in north-western Australia.

Habitat. Epilithic in intertidal pools and drift in north-western Australia.

[After J.M. Huisman & O. De Clerck in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 290–291 (2018)]