Porolithon imitatum R.A.Towns. & G.W.Saunders

Scientific Description

Habit and structure. Thallus encrusting, uniformly smooth, shiny when dry, sometimes appearing speckled (due to megacyte fields), pale rose pink with tinges of grey-green, 130–3000 μm thick, often with thickened margins; surface often with parallel marks produced by the radulae of grazing gastropods. Inner portions of the thallus often invaded by boring organisms and appearing green due to the density of endophytic cyanobacteria. Medulla plumose, up to 20% of thallus thickness at the leading edges, up to 13–60 μm thick; cells 7–24 μm long, 3–13 μm diam., with occasional lateral fusions between adjacent filaments. Cortex multilayered, composed of cells 2.5–27 μm long, 3–8 μm diam., with lateral and oblique fusions between cells of adjacent filaments. Cortical megacytes often visible on thallus surface in pustulate fields surrounded by a rim; individual megacytes 9–20 μm long, 9–20 μm diam.; megacyte fields becoming buried in the cortex, their appearance changing to resemble modified cortical cells. Intercalary initials 8–15 μm long, 3–8 μm diam. Epithallium of 1 (–3) rounded cells 4–8 μm long, 4–8 μm diam., the outermost cell usually devoid of cytoplasm.

Reproduction. Tetrasporangial conceptacles slightly sunken to flush with the thallus surface, some with a raised peripheral ring, reniform in section, 175–200 μm internal diam., 75–90 μm internal height. Conceptacle roof 4 cell layers thick; pore 31–37 μm long, lined with large inwardly facing cells 24–34 μm long, 12–15 μm diam. Older conceptacles becoming buried in cortex due to thallus growth. Other reproductive stages not observed.

Distribution. Dampier Archipelago north to Long Reef, Western Australia.

Habitat. epilithic in the intertidal and subtidal.

[After R.A. Townsend & J.M. Huisman in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 123–124 (2018)]