Sporolithon ptychoides Heydr.

Scientific Description

Habit and structure. Thallus encrusting to fruticose, attached or as rhodoliths. Thallus 150–1050 μm thick, with branches up to 6 mm long, laterally flattened, 3–7 mm wide. Medullary filaments in a plumose pattern; cells 15–25 μm long, 4–10 μm diam. Cortex multilayered, with secondary pit connections and lateral fusions between cells of adjacent filaments. Cortical cells 7–20 μm long, 7–10 μm diam. Cortical cell filaments ending in an initial 6–10 μm long, 6–9 μm diam. Initials subtending a single layer of flattened epithallial cells 2–3 μm long, 10–12 (–15) μm diam.

Reproduction. Gametangial conceptacles not seen. Carposporangial conceptacles raised, 150–220 μm internal diam.; roof at 30–60 μm below the thallus surface; pore 20–40 μm diam., old conceptacles buried in thallus as areas of ingrowth and recalcification; carposporangia across the floor and walls of the conceptacle, elliptical to oblong or ovate, 31–70 μm long, 9–40 μm diam. Tetrasporangia in circular to irregularly shaped sori that are slightly raised (up to 75 μm) above the thallus surface, 375–600 μm long, 76–300 μm wide; loculi 70–85 μm high and 48–55 μm wide. Sori becoming buried in thallus. Tetrasporangial locules surrounded by calcified filaments of 2 or 3 long cells (15–25 μm long, 5.0–7.5 μm diam.) subtending 2 or 3 shorter cells within the sorus. Tetrasporangia 38–63 μm long, 29–36 μm diam., decussate, each situated below a pore 9–12 μm diam.

Distribution. Widespread in warmer waters of the Indo-Pacific and the Mediterranean Sea.

Habitat. Sporolithon ptychoides is often found intertidally with Hydrolithon reinboldii forming free-living rhodoliths.

[After R.A. Townsend & J.M. Huisman in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 146 (2018)]