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Electronic Flora of South Australia Genus Fact Sheet
Phylum Rhodophyta – Class Florideophyceae – Order Gigartinales – Family Areschougiaceae
Thallus erect, much branched (especially above) irregularly radially, branches terete; holdfast discoid. Structure uniaxial, each axial cell with a single periaxial cell, forming a medulla of periaxial filaments, soon filled with rhizoids, and a pseudoparenchymatous cortex 3–4 (–7) cells broad; axial filament conspicuous throughout.
Reproduction: Sexual thalli monoecious; procarpic. Carpogonial branches 3-celled, borne on outer medullary cells, directed sideways with the trichogyne more or less straight, with occasional sterile cells on the basal cell. Connecting filaments unknown. Auxiliary cell the next outer cell to the supporting cell, with adjacent cells producing secondary nutritive tissue. Gonimoblast initial first inwards, becoming radial from the prominent fusion cell (with the periaxial filament forming a fusion stalk) and producing short chains of ovoid carposporangia. Cystocarps without enveloping tissue but swelling branchlets, ostiolate. Spermatangia scattered, cut off from outer cortical cells.
Tetrasporangia scattered in the outer cortex, developed from mid cortical cells and basally pit-connected, zonately divided.
Life history triphasic with isomorphic gametophytes and tetrasporophytes.
Type species: M. dumosum (Harvey) Min-Thein & Womersley 1976: 69.
Taxonomic notes: Melanema differs from Areschougia in having a gradual merging of medulla to cortex, in being procarpic with the auxiliary cell next to the supporting cell and probably involving direct fusion between the fertilized carpogonium and the auxiliary cell (connecting filaments are apparently not formed), and in lack of enveloping tissue around the carposporophyte. The carpogonial branches of Melanema are also relatively straight, directed more or less outwards. In other reproductive respects Melanema agrees with Areschougia, but the above differences mean either that the family Areschougiaceae must be broadened or a different position found for Melanema. The carpogonial branch orientation and lack of any enveloping tissue may ally Melanema more with the Caulacanthaceae, but it is left in the Areschougiaceae pending further study (see also Gabrielson & Hommersand 1982a, p. 44).
References:
GABRIELSON, P.W. & HOMMERSAND, M.H. (1982a). The Atlantic species of Solieria (Gigartinales, Rhodophyta): their morphology, distribution and affinities. J. Phycol. 18, 31–45.
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.
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.
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