Ceramium australe Sond.

Scientific Description

Habit and structure. Thallus brown-red to dark red, 1–4(–6) cm high, regularly subdichotomous in varied planes, without proliferous branchlets, with several erect branches arising from slight, prostrate, basal filaments. Attachment by uniseriate-celled rhizoids which may develop multicellular pads, arising from the periaxial (occasionally pseudoperiaxial) cells; epiphytic on seagrasses or red algae. Structure. Branches (160–)200–300 µm in diameter below, decreasing gradually to 100–150 µm in diameter near the apices, then tapering more abruptly to the strongly involute apices. Axial cells isodiametric near apices, L/D (1–)2–2.5(–3) below, with regular, straight margined, bands of nodal cortication mostly 80–120 µm long, separated by an internodal space 0.2–1 times the nodal length above and 2–3 times in the lower parts. Periaxial cells 6–7, each cutting off laterally (within the periaxial cell ring) two slightly smaller pseudoperiaxial cells, each of which cuts off one cell acropetally and basipetally, these then dividing to form one or two cells which usually divide again, forming nodal cortication (5–)7 cells long; the true periaxial cells cut off one cell acropetally and this cuts off one or two more, but no cells are cut off basipetally; first acropetal derivative of the periaxial cells commonly cutting off a large gland like cell; no outer cortex is formed. Rhodoplasts discoid in small cells becoming ribbon like in larger cells.

Reproduction. Carposporophytes and spermatangia unknown. Tetrasporangia produced in irregular abaxial series, with up to 3 per node formed successively, spreading around the node, cut off acropetally from periaxial cells, slightly basally involucrate by cortical filaments with slightly longer cells than in sterile nodes; tetrasporangia subspherical to pyriform, irregularly horizontally divided into bispores (in plants observed), 55–75 µm in diameter.

Distribution. Shark Bay, W. Aust., to Walkerville, Vic., and N Tas.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIC: 404–407 (1998)]