Electronic Flora of South Australia Species Fact Sheet
Phylum Rhodophyta – Class Florideophyceae – Order Gigartinales – Family Areschougiaceae
Selected citations: Kylin 1932: 36, fig. 7D–G, pl. 14 fig. 35; 1956: 289, fig. 220C. Lucas & Perrin 1947: 173. Min-Thein & Womersley 1976: 48, fig. 55B.
Thallus (Fig. 113C) medium to dark red-brown, fading to yellow-grey, 5–15 cm high, moderately to much branched with 2–4 (–6) branches from the apex of each segment; mature segments elongate-ovoid to clavate, 0.5–2 cm long, 1–2 (–3) mm in diameter; lower segments not or only slightly thickened, 0.5–1 mm in diameter, without adventitious laterals. Holdfast stoloniferous and hapteroid, 0.5–2 cm across, with several axes; epilithic. Structure uniaxial, with rhizoidal filaments enlarging to form a core of 4–6 similar filaments 8–20 µm in diameter together with slenderer filaments, surrounded by a broad, lax medulla of periaxial filaments with divergent end cells lying just inside the cortex, some cells becoming very long, 4–8 µm in diameter, with uniform, refractive contents. Cortex pseudoparenchymatous, 2 (–3) cells thick, inner cells ovoid and 12–20 (–30) µm in diameter, outer cells (8–) 10–16 (–20) µm in diameter. Rhodoplasts ovoid to elongate, becoming ribbon shaped, several per cell.
Reproduction: Sexual thalli monoecious; non-procarpic. Carpogonial branches 3-celled, 1 (–2) borne on inner cortical cells, directed inwards with reflexed trichogynes. Connecting filaments not observed. Auxiliary cell an inner cortical cell which becomes darkly staining, with attached outer cortical cells dividing into short chains. First gonimoblast cut off inwardly, later radially from the developing fusion cell, the carposporophyte (Fig. 113D) producing short chains of ovoid carposporangia (terminally mature) 20–30 µm in diameter, sometimes germinating before release. Cystocarps lying within the medulla, enveloping tissue absent, cortex thickened around the narrow ostiole. Spermatangia scattered or in small patches, with surface cortical cells cutting off 3–4 initials which form 2–3 ovoid spermatangia each 1.5–2 µm in diameter.
Tetrasporangia (Fig. 113E) scattered in the cortex, laterally pit-connected to an inner cortical cell, protruding into the medulla, ovoid, 40–70 µm long and 30–60 µm in diameter, zonately divided.
Type from Western Port, Vic. (Harvey, Alg. Aust. Exsicc. 392); holotype in Herb. Agardh, LD, 34531; isotype in MEL, 44575.
Selected specimens: Point Sinclair, S. Aust., drift (Womersley, 25.i.1951; AD, A13852). 4 km W of Waldegrave I., S. Aust., 30 m deep (Branden, 3.vii.1987; AD, A57594). Investigator Strait, S. Aust., 33 and 43 m deep (Watson, 24.i.1971; AD, A41127 and A38146 resp.). 3 km SE of Troubridge I., S. Aust., 24 m deep (Shepherd, 5.ii.1969; AD, A33897). Vivonne Bay, Kangaroo I., S. Aust., drift (Womersley, 17.i.1950; AD, Al2628). Nora Creina, S. Aust., drift (Gordon, 26.i.1967; AD, A31637). Western Port, Vic. (Wilson, 9.i.1885; MEL, 502102).
Distribution: Point Sinclair, S. Aust., to Western Port, Vic.
Taxonomic notes: Rhabdonia clavigera is a deep-water species characterised by the segment dimensions, medullary core of 4–6 filaments of similar size, and the presence of long, refractive, cells with uniform contents just inside the cortex.
AGARDH, J.G. (1872). Bidrag till Florideernes Systematik. Acta Univ. hind. 8, 1–60.
AGARDH, J.G. (1876). Species Genera et Ordines Algarum. Vol. 3, Part 1 - Epicrisis systematis Floridearum, pp. i-vii, 1–724. (Weigel: Leipzig.)
AGARDH, J.G. (1897). Analecta Algologica. Cont. IV. Acta Univ. lund. 33, 1–106, Plates 1, 2.
KYLIN, H. (1932). Die Florideenordnung Gigartinales. Lunds Univ. Årsskr. N.F. Avd. 2, 28 (8), 1–88, Plates 1–28.
KYLIN, H. (1956). Die Gattungen der Rhodophyceen. (Gleerups: Lund.)
LUCAS, A.H.S. & PERRIN, F. (1947). The Seaweeds of South Australia. Part 2. The Red Seaweeds. (Govt Printer: Adelaide.)
MIN-THEIN, U. & WOMERSLEY, H.B.S. (1976). Studies on southern Australian taxa of Solieriaceae, Rhabdoniaceae and Rhodophyllidaceae (Rhodophyta). Aust. J. Bot. 24, 1–166.
The Marine Benthic Flora of Southern Australia Part IIIA complete list of references.
Womersley, H.B.S. (14 January, 1994)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIIA, Bangiophyceae and Florideophyceae (to Gigartinales)
Reproduced with permission from The Marine Benthic Flora of Southern Australia Part IIIA 1994, by H.B.S. Womersley. Australian Biological Resources Study, Canberra. Copyright Commonwealth of Australia.
Illustration in Womersley Part IIIA, 1994: FIG. 113 C–E.
Figure 113 enlarge
Fig. 113. A. Rhabdonia coccinea (AD, A61214). Habit. B. Rhabdonia verticillata (AD, A41031). Habit. C–E. Rhabdonia clavigera. (C, AD, A31637; D, E, AD, A57594). C. Habit. D. Transverse section of branch with a carposporophyte with central fusion cell and radiating gonimoblast filaments with terminal carposporangia. E. Transverse section of cortex with tetrasporangia.
State Herbarium of South Australia