Electronic Flora of South Australia Family Fact Sheet
Phylum Rhodophyta – Class Florideophyceae – Order Gigartinales
Thallus erect, cartilaginous, much branched irregularly or subdichotomously, branches terete or compressed. Structure uniaxial, with 3 or 4 periaxial cells (the lateral two developing more strongly in compressed taxa), the axial filament remaining prominent or not, medulla of thick-walled rhizoidal filaments, cortex pseudoparenchymatous with secondary pit-connections between inner cells.
Reproduction: Sexual thalli monoecious or dioecious; procarpic and usually polycarpogonial. Carpogonial branches 3-celled, borne in a cluster of filaments with an intercalary auxiliary cell. Fertilized carpogonium forming a single connecting filament which fuses with the auxiliary cell, which then emits a single gonimoblast initial towards the thallus surface. Carposporophytes with outwardly radiating gonimoblast filaments from a basal fusion cell, with terminal chains of carposporangia, within a protruding, ostiolate pericarp. Spermatangia in clusters on the upper cells of uniseriate, branched filaments growing in tufts from the thallus surface.
Tetrasporangia borne on uniseriate branched filaments on the thallus surface, sessile, cruciately divided.
Life history triphasic with isomorphic gametophytes and tetrasporophytes.
Taxonomic notes: A small family of two genera (3 species) found on southern Australian coasts, distinguished by the formation of spermatangia and tetrasporangia on uniseriate filaments extending in tufts from the thallus surface, and apparently readily lost. The globular, basally constricted cystocarps with a basal fusion cell and dense, radiating gonimoblast filaments with terminal chains of carposporangia, and the dense medulla of thick walled rhizoids (similar to the rhizines of Gelidiales) are also characteristic.
Development of procarps and cystocarps was studied by Searles (1968) and the spermatangial and tetrasporangial reproduction by Womersley (1971b). Some aspects of their reproduction still need clarification.
SEARLES, R.B. (1968). Morphological studies of red algae of the order Gigartinales. Univ. Calif Pubis Bot. 43, vi + 1–86, Plates 1–12.
WOMERSLEY, H.B.S. (1971b). The relationships of Nizymenia and Stenocladia (Gigartinales, Rhodophyta). Phycologia 10, 199–203.
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.
KEY TO GENERA OF NIZYMENIACEAE
1. Thallus compressed, axial filament not visible in mature branches
1. Thallus compressed or terete, axial filament conspicuous throughout the thallus
State Herbarium of South Australia