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Medeiothamnion repens Gordon 1972: 65, figs 19–21, 56B.

Phylum Rhodophyta – Order Ceramiales – Family Ceramiaceae – Tribe Sphondylothamnieae

Thallus (Fig. 40A) red-brown, with prostrate main axes and erect branches 2–5 mm high, attached by haptera; epiphytic on receptacles (and vesicles) of Cystophora platylobium and C. siliquosa. Structure. Sub-apical cells of prostrate axes (Fig. 40B) bearing 3 (–5) whorl-

branchlets, 1 (or 2) of which are erect and to 5 mm high, the others prostrate and smaller, one on each side of the erect whorl-branchlet; erect whorl-branchlets (Fig. 40B) more or less pectinately and adaxially branched, median cells 60–140 µm in diameter and L/D 2.5–4; prostrate axial cells 180–200 µm in diameter and L/D 2–5. Indeterminate branches produced in position of prostrate whorl-branches. Cortication absent. Haptera produced in pairs from proximal ends of axial cells, often with additional small branchlets and haptera later. Cells multinucleate; rhodoplasts discoid.

Reproduction: Gametophytes dioecious. Female axes (Fig. 40C) developing in position of an erect whorl-branchlet, (4–) 6–9 (–14) cells long; procarps as for the genus, with the subapical cell producing 2 sterile pericentral cells and a supporting cell with a sterile cell and a carpogonial branch (Fig. 40C), the larger subhypogenous cell with an involucral filament. Post-fertilization, the auxiliary cell fuses with adjacent cells and the fusion cell cuts off gonimoblast cells, with the carposporophyte (Fig. 40D) 450–680 µm across, carposporangia clavate and 25–65 µm in diameter. Three inner involucral filaments are formed from the apical cell, supporting sterile cell and one sterile pericentral cell. Spermatangial heads (Fig. 40E) are ovoid, 50–60 µm in diameter, and terminal on short laterals on the upper parts of erect whorl-branchlets.

Tetrasporangia (Fig. 40F) are sessile or stalked on the lower cells of erect whorl-branchlets, 80–100 µm in diameter, tetrahedrally divided.

Type from Kingston, S. Aust., on Cystophora platylobium (Womersley, 19.viii.1966; holotype in AD, A30665).

Selected specimens: Elliston, S. Aust., on Cystophora siliquosa, pools on reef (Gordon, 16.v.1968; AD, A32159). Corny Point, Yorke Pen., S. Aust., on Cystophora siliquosa, drift (Gordon, 23.ix.1968; AD, A32162). Daly Head, Yorke Pen., S. Aust., on C. platylobium, drift (Gordon, 26.iii.1967; AD, A31010). South West R. mouth, Kangaroo I., S. Aust., on C. platylobium, drift (Gordon, 19.xi.1967; AD, A31212). Seal Bay, Kangaroo I., S. Aust., on C. siliquosa, drift (Gordon, 20.xi.1967; AD, A31445).

Distribution map based
on current data relating to
specimens held in the
State Herbarium of SA

Distribution: Known from Elliston, SW Yorke Pen., the S coast of Kangaroo I., and Kingston, S. Aust; probably more widely distributed but inconspicuous.

Taxonomic notes: Medeiothamnion repens is an inconspicuous but distinctive epiphyte known from two species of Cystophora, but is probably of wider distribution.


GORDON, E.M. (1972). Comparative morphology and taxonomy of the Wrangelieae, Sphondylothamnieae and Spermothamnieae (Ceramiaceae, Rhodophyta). Aust. J. Bot. suppl. 4, 1–180.

The Marine Benthic Flora of Southern Australia Part IIIC complete list of references.

Author: H.B.S. Womersley

Publication: Womersley, H.B.S. (24 December, 1998)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIIC. Ceramiales – Ceramiaceae, Dasyaceae
©State Herbarium of South Australia, Government of South Australia

Illustration in Womersley Part IIIA, 1998: FIG. 40.

Figure 40 image

Figure 40   enlarge

Fig. 40. Medeiothamnion repens (AD, A30665). A. Habit, on Cystophora platylobium. B. Prostrate axes with erect and prostrate whorl-branchlets, with tetrasporangia. C. Axis with a mature procarp. D. Mature carposporophyte and involucral branches. E. Longitudinal section of a spermatangial head, with a juvenile stage. F. Whorl-branchlets with tetrasporangia. (All as in Gordon 1972, courtesy of Aust. J. Bot.)

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