Ceramium macilentum J.Agardh

Scientific Description

Habit and structure. Thallus erect, to 3–4 mm tall, subdichotomously to subalternately branched, with involute apices. Axial cells 40–50 µm diam. near the apices [L:B c. 1], to 50–60 µm diam. near the base [L:B 2–3]. Nodes 2 or 3 cells long, with up to 6 periaxial cells, each cutting off laterally a pseudoperiaxial cell resulting in a ring of 10–12 cells. Both periaxial and pseudoperiaxial cells cutting off 1 or 2 cells acropetally; these can divide further. Basipetal divisions absent or very rare.

Reproduction. Spermatangia in tufts on outer cortical cells, initially abaxial, eventually covering the node. Carpogonial branch and cystocarps forming near branch apices, eventually laterally displaced by growth of the subtending axis, with 3 or 4 adventitious involucral branches. Carposporophyte with 1–3 sequentially maturing gonimolobes to 180 µm diam., composed entirely of carposporangia. Tetrasporangia in adaxial clusters of 1–3 sporangia, basally involucrate to about half the sporangium, decussately to tetrahedrally divided, 50–55 long, 30–35 µm diam., obovoid to slightly pyriform. Other reproductive structures not observed.

Distribution. Widely distributed in tropical seas and extending into temperate waters in southern Australia.

Habitat. Epiphytic in the intertidal and subtidal.

[After J.M. Huisman in Algae of Australia: Marine Benthic Algae of North-western Australia, 2. Red Algae: 400–401 (2018)]