Electronic Flora of South Australia Species Fact Sheet

Platoma australica Womersley & Kraft, sp. nov.

Phylum Rhodophyta – Class Florideophyceae – Order Gigartinales – Family Nemastomataceae

Thallus (Fig. 89D) medium red, fading to yellow-red, slightly mucilaginous, (10–) 15–35 cm high and 15–25 cm across, foliose with a few major lobes and a smooth to somewhat irregular margin, surface slightly mottled and with slight furrows on the lower thallus, 300–600 (–1000) µm thick, broadening markedly from a short stipe 3–8 mm long and 2–3 mm in diameter. Holdfast discoid, 2–4 mm across; epilithic. Structure of a cortex (Fig. 90G) 60–80 µm thick, of discrete branch systems 6–8 cells long, inner cortex subdichotomous at each cell, cells ovoid to subspherical, 10–12 µm in diameter, tapering to the outer cortex of slightly separated filaments 2–4 (–5) µm in diameter, cells cylindrical, L/D (1–) 2–3, unbranched for terminal 2–3 cells; medulla of lax filaments 4–6 µm in diameter, some traversing from cortex to cortex. Rhodoplasts few per cell, discoid to elongate.

Reproduction: Sexual thalli monoecious. Carpogonial branches (Fig. 900) 3-celled, borne on an inner cortical (supporting) cell with adjacent cells becoming swollen and darkly staining, the branch systems borne on the supporting cell of normal cortical length. Auxiliary cells in a similar position to the supporting cell, becoming swollen and subspherical and with adjacent cells darkly staining, producing the gonimoblast directly following union with a connecting filament. Carposporophyte (Fig. 90H) lying between the cortical systems but protruding into the outer medulla, ovoid to conical, 60–80 µm across, all cells becoming ovoid carposporangia 6–10 pm in diameter. Cortical filaments around the carposporophyte with enlarged cells but only a slight pore in the outer cortex above the carposporophyte. Spermatangia (Fig. 90I) cut off from the outer cortical cells, ovoid, 1–2 µm in diameter.

Tetrasporangia unknown.

Type from Encounter Bay, S. Aust., drift (Womersley, 1.ii.1976); in AD, A46962.

Selected specimens: Waldegrave I., S. Aust., 22 m deep (Shepherd, 17.iv.1970; AD, A35890). Elliston, S. Aust., drift (Woelkerling, 28.xii.1976; AD, A47863). Victor Harbor, S. Aust., drift (Womersley, 22.ix.I990; AD, A60587). Vivonne Bay, Kangaroo I., S. Aust., 5–6 in deep on jetty piles (Kraft 4709, 19.i.1974; AD, A47280). Victor Harbor, S. Aust., drift (Womersley, 22.ix.1990; AD, A60587). Baudin Rocks, Guichen Bay, S. Aust., 6 m deep (Owen & Lewis, 16.ii.1974; AD, A47226). Stinky Bay, Nora Creina, S. Aust., drift (Womersley, 14.iii.1991; AD, A61171). Port MacDonnell, S. Aust., drift (Womersley, 23.viii.1988; AD, A59244). West Point, Erith I., Kent Group, Bass Strait, 28 m deep (Shepherd & Lewis, 10.v.1974; AD, A45120). Taroona, Tas., uppermost sublittoral (Sanderson, 24.xi.1991; AD, A61534).

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

Distribution: Waldegrave I., S. Aust., to Kent Group, Bass Strait, and SE Tasmania.

Taxonomic notes: P. australica is a deep water species on rough-water coasts. It is superficially similar to both P. foliosa and Schizymenia dubyi, differing from the former in lack of marginal lobes, in having a narrower cortex, and in the cortical filaments on the supporting cell being of normal length. The cortex of Schizymenia dubyi is of similar thickness but is more compact, with the branch systems separating less easily on squashing, and also differs in having a distinct ostiole surrounded by modified cortical filaments outside the carposporophyte.

References: The Marine Benthic Flora of Southern Australia Part IIIA

Author: by H.B.S. Womersley & G.T. Kraft

Publication: 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.

Illustrations in Womersley Part IIIA, 1994: FIGS 89D, 90 G–I.

Figure 89 image

Figure 89   enlarge

Fig. 89. A, B. Schizymenia dubyi (A, AD, A61539; B, AD, A41187). A. Habit, young plants. B. Habit, old plant. C. Platoma foliosa (AD, A42227). Habit. D. Platoma australica (AD, A46962). Habit.

Figure 90 image

Figure 90   enlarge

Fig. 90. A–C. Schizymenia dubyi (A, B, AD, A34879; C, AD, A34856). A. Transverse section of cortex with gland cells and carpogonial branch with adjacent darkly staining cells. B. Transverse section of cortex and depressed ostiole, with a young carposporophyte. C. Outer cortical cells with spermatangia. D–F. Platoma foliosa (AD, A42227). D. Section of cortex with carpogonial branch and adjacent darkly staining cells. E. Cortex with auxiliary cell and connecting filament, and carposporophyte. F. Outer cortex with spermatangia. G–I. Platoma australica (G, AD, A46962; H, I, AD, A45120). G. Transverse section of cortex with a carpogonial branch and adjacent darkly staining cells (two cells with rhodoplasts). H. Carposporophyte. I. Outer cortex with spermatangia.

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