Ramicrusta appressa K.R.Dixon

Scientific Description

Habit and structure. Thallus reddish brown to brown, closely appressed but not always tightly adherent to the substratum. Hypothallus as for the genus. Perithallus composed of a heavily calcified lower part 135–325 µm thick, and a thin (c. 25 µm) weakly calcified epithallus 2–4 cells thick. Cells of the lower perithallus comparatively large, 20–45 µm diam. below, gradually decreasing in size distally, thick-walled and frequently forming secondary pit connections to adjacent cells. Epithallial cells 7–18 µm diam., deeply pigmented, not developing secondary pit connections. Hair cells deeply embedded within the epithallus and borne on upper cells of the lower perithallus, bullet-shaped, 20–32 µm long and 20–25 µm diam., the distal portion of the hair cell clear. Rhizoids robust, unicellular, to 240 µm long, c. 17 µm diam., cut off the distal ventral corners of hypothallial cells.

Reproduction. Carpogonial branches 2-celled. Other reproductive features not seen.

Distribution. A rather rare species in north-western Australia; also in Vanuatu and the Philippines.

[After K.R. Dixon in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 236–237 (2018)]