Electronic Flora of South Australia Family Fact Sheet
Phylum Rhodophyta – Class Florideophyceae – Order Gigartinales
Thallus erect, much branched irregularly to distichously, with terete to slightly or strongly compressed branches, sometimes proliferous, holdfast discoid or stoloniferous. Structure uniaxial, distinct near the apices with each axial cell producing two periaxial cells and filaments, with cross-connector cells and abundant slender rhizoids from the axial cells forming a filamentous medulla in which the original axial filament becomes inconspicuous in most species, surrounded by several large cells (the original periaxial cells) and other medium-sized cells with rhizoidal filaments between them, and a small-celled cortex; secondary pit-connections abundant; most cells multinucleate.
Reproduction: Sexual thalli monoecious; procarpic and polycarpogonial. Carpogonial branches borne on inner cortical cells in localized fertile areas, directed sideways or outwards; supporting cells acting as auxiliary cells, diploidized via a short tube from the fertilized carpogonium. Gonimoblast initials arising laterally and thallus inwardly, with further development thallus inwardly and gonimoblast filaments forming secondary pit-connections to vegetative cells. Peripheral gonimoblasts separating from the auxiliary cell and forming isolated groups which form carposporangial primordia and then carposporangia, at maturity densely filling pockets between sterile cells. Cystocarps immersed and swelling branchlets, or protuberant, lacking fusion cells and ostioles, and usually with no or slight filamentous enveloping tissue except when protuberant. Spermatangia formed in scattered, sunken, clusters in the outer cortex, with a ring of initials each producing 2 to a few spermatangia.
Tetrasporangia formed from outer cortical cells (in two species intercalary), scattered (nemathecial in one species), zonately divided.
Life history triphasic with isomorphic gametophytes and tetrasporophytes.
Taxonomic notes: The family contains a single genus Mychodea, with 11 species all confined to southern Australia (Kraft 1978).
KRAFT, G.T. (1978). Studies of marine algae in the lesser-known families of the Gigartinales (Rhodophyta). III. The Mychodeaceae and Mychodeophyllaceae. Aust. J. Bot. 26, 515–610.
KYLIN, H. (1932). Die Florideenordnung Gigartinales. Lunds Univ. Årsskr. N.F. Avd. 2, 28 (8), 1–88, Plates 1–28.
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.
State Herbarium of South Australia