Ceramium puberulum Sond.

Scientific Description

Habit and structure. Thallus light red to dark red-brown, erect, 4–10 cm high, much branched irregularly, laterally to subdistichous, sometimes with proliferations from older axes. Attachment by numerous, branched, uniseriate-celled rhizoids originating from the periaxial cells for several segments above the base of the erect axis, descending within the cortex and forming a compact discoid holdfast; usually epiphytic on seagrasses (usually Posidonia but also on Amphibolis). Structure. Branches 0.5–1 mm in diameter near the base, mid parts 100–250 µm, upper parts 45–125 µm in diameter. Axial cells L/D 0.5–2 below, above L/D 1–4. Periaxial cells 7(–8) each cutting off 2(–3) smaller cortical cells both acropetally and basipetally which further divide to form nodes (6–)8–12 cells long in upper parts with narrow to distinctly longer internodal spaces, with the nodal cortication extending on older parts to become continuous near the thallus base; many plants show moniliform lower branches due to constriction of axial cells between the nodal cortication. Outer cortex forming a more-or-less continuous layer of small cells overlying the larger elongate inner cortical cells. Spines (primary) one to several per node near apices, 30–40(–60) µm and up to 4 cells long, usually relatively slender; primary spines usually soon lost but cortex of lower segments becoming covered with numerous short slender secondary spines (1–)2(–3) cells long arising from the outer cortical cells; spines which arise near the apices always larger than lower later formed spines; numerous fine hairs up to 250 µm long arising from nodal cortical cells in some plants. Rhodoplasts discoid to elongate in smaller cells, becoming ribbon like in axial cells.

Reproduction. Gametophytes dioecious. Carposporophytes globular, 150–350 µm across, with ovoid carposporangia 30–55 µm in diameter, borne on upper branches and surrounded by several small, lateral, involucral branchlets. Spermatangia in dense patches covering the nodal cells of upper branches. Tetrasporangia at first single per node, later several, cut off from one or more periaxial cells usually abaxially, 50–100 µm in diameter, tetrahedrally to decussately divided, prominent but usually becoming entirely enveloped by small involucral cells (some bearing spines); the several tetrasporangia within the involucre form prominent, often scattered, enlarged nodes along the branches, though less so in young, slender plants.

Distribution. Shark Bay, W. Aust., around southern Australia to Jervis Bay, N.S.W., and northern Tas.

Habitat. C. puberulum is a common epiphyte on Posidonia throughout its geographical range and is less frequently found on Amphibolis; it is rare on other hosts.

[After Womersley, Mar. Benthic Fl. Southern Australia IIIC: 388–389 (1998)]