Lithothamnion proliferum Foslie

Scientific Description

Habit and structure. Thallus encrusting to fruticose, monomerous, 230–1400 μm thick, often with a white rim 130–460 μm wide. Branches to 3 mm long, either terete (2.5–3.0 mm diam.) or compressed (3–7 mm wide); in deeper water mostly unbranched and forming a thick crust. Medulla up to 60% of thallus thickness at the margins; cells rarely fusing laterally, (5–) 10–25 μm long, 12–22 μm diam. Apical initials triangular 4.8–7.3 μm wide at the base and 9.5–14.6 μm long. Cortex multilayered, with lateral and diagonal fusions common between cells of up to 5 adjacent filaments; cells 2.5–12.5 μm long, 3.0–5.8 μm diam.; cell filaments ending in an initial 3.0–6.5 μm long, 4.5–10.0 μm diam. Initials subtending a single layer of flattened epithallial cells 2.0–2.5 μm long, 4.5–10.0 μm diam.

Reproduction. Sporangial conceptacles circular (rarely elliptical), on the apices of branches, not raised above the thallus surface, 640–950 μm outside diam., 720–1145 μm internal diam., c. 175 μm internal height. Conceptacles appearing as slightly dull areas on thallus surface, becoming buried in the thallus; roof up to 7 cell layers thick, with no visible difference between the pore cells and roof cells. Sporangia surrounded by filaments within the conceptacle lumen; each situated below an occluded pore 7–12 μm diam., 80–100 μm long, 30–50 μm diam., in the form of tetrasporangia; apical spore constricted to a peak by conceptacle roof. Female conceptacles raised, 480–720 μm internal diam., 120–150 μm internal height; fertile area across floor of the conceptacle; pore height 250–360 μm. Fertilisation of individual carpogonial branches resulting in the formation of carposporangia across the floor of the conceptacle. Carposporangial conceptacles immersed in the thallus, 850–1200 μm internal diam., 300–360 μm internal height, with carposporangia 24–50 μm diam., 45–85 μm long. Male conceptacles slightly raised, to 100 μm high, with a prominent pore, 500–750 μm outside diam.; internal morphology not observed.

Distribution. Found in the tropical western and central Pacific Ocean.

Habitat. In shallow waters, this species inhabits darker crevices in reefs.

[After R.A. Townsend & J.M. Huisman in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 133–134 (2018)]