Porolithon penroseae R.A.Towns. & P.W.Gabrielson

Scientific Description

Habit and structure.  Thallus encrusting to lumpy, dull pink to mauve, 30–700 μm thick, often with thickened margins, monomerous in construction; surface often with parallel marks produced by the radulae of grazing gastropods. Thallus often overgrowing itself. Medulla multilayered, up to 10% of thallus thickness at maturity, of branched filaments. Cortex multilayered, with cells 5–27 μm long, 2.5–8.0 μm diam. Cortical filaments with lateral fusions between cells of adjacent filaments, each ending in an intercalary initial cell that subtends 1 (or 2) transversely elliptical to laterally transverse ovate epithallial cells 5–8 μm long and diam.; intercalary initials 7–10 μm long, 2–10 μm diam. Megacyte fields scattered throughout the upper cortex, easily seen with a dissecting microscope (but not evident deeper in the cortex), with a ragged edge, lacking a rim and becoming buried in the cortex, their appearance changing to resemble modified cortical cells. Megacytes 32–37 μm long, 14–20 μm diam.

Reproduction. Male conceptacles immersed in the cortex, to 200 μm internal diam. Carposporangial conceptacles depressed-ovate, 100–125 μm outside diam., immersed in the cortex; pore distinct at maturity. Tetrasporangial conceptacles flush with the surface or very slightly raised, 85–200 μm outside diam., c. 110 μm internal diam., c. 75 μm internal height; pore 4 cell layers below the roof, lined with large cells, triangular in LS, 21–26 μm long, 7–15 μm diam. Tetrasporangia 80–190 μm long, 35–72 μm diam.

Distribution. North-western Australia.

Habitat. intertidal to subtidal.

[After R.A. Townsend & J.M. Huisman in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 125–126 (2018)]