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Phylum Rhodophyta – Class Florideophyceae – Order Gigartinales

Thallus erect, occasionally prostrate, foliose to much branched subdichotomously or pinnately to irregularly, branches terete to compressed, firm and drying cartilaginous; holdfast usually discoid. Structure multiaxial, growth apical and subapical, developing a lax filamentous medulla of elongate cells and a cortex of anticlinal filaments of small cells, with secondary pit-connections in the inner cortex of ovoid cells, in a firm gelatinous matrix; pit-plugs with no cap layers.

Reproduction: Sexual thalli monoecious or dioecious, procarpic. Carpogonial branches 3-celled, situated on a supporting cell which is an inner cortical cell and which bears a sterile cortical branch. Auxiliary cell transformed from the supporting cell, developing gonimoblast filaments primarily thallus inwardly and forming an entangled mass of slender filaments mixed with small clusters of carposporangia; filamentous enveloping tissue usually present around the carposporophyte. Mature cystocarps embedded or protuberant; ostiole absent, though cortex often depressed outside the carposporophyte, carpospores usually released by breakdown of cortical filaments. Spermatangia cut off from outer cortical cells in irregular patches.

Tetrasporangia formed in inner cortical or medullary sori by transformation of inner cortical or medullary cells or by apical and lateral divisions of these cells, cruciately divided.

The family Gigartinaceae has been restricted and unified by separation of heteromorphic taxa [with a crustose tetrasporophyte (Petrocelis)] to Mastocarpus in the family Petrocelidaceae. Recognition of seven genera is proposed by Hommersand et al. (1993), but some of these are probably of subgeneric status within Gigartina (see below). Based on this proposed scheme, no species of Iridaea, Chondrus, Chondracanthus, or Mazzaella are known in southern Australian waters.

Life history triphasic with isomorphic gametophytes and tetrasporophytes, occasionally with mixed phases.


HOMMERSAND, M.H., GUIRY, M.D., FREDERICQ, S. & LEISTER, G.L. (1993). New perspectives in the taxonomy of the Gigartinaceae (Gigartinales, Rhodophyta). Hydrobiologia 260/261 (Proc. Intn. Seaweed Symp. 14), 105–120.

KÜTZING, F.T. (1843). Phycologia generalis. (Leipzig.)

The Marine Benthic Flora of Southern Australia Part IIIA complete list of references.

Author: H.B.S. Womersley

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.


1. Thallus foliose, simple or lobed, submembranous; cystocarps immersed in the thallus; tetrasporangia developed by apical divisions of cortical cells, remaining in rows radiating inwards from just inside the outer cortex


1. Thallus foliose or much branched subdichotomously to laterally, cartilaginous; cystocarps protuberant, in emergent papillate outgrowths or branchlet ends; tetrasporangia developed by transformation or lateral divisions of inner cortical or outer medullary cells or from inward-growing clusters of cells in the mid medulla, not in distinct rows radiating inwards from the subsurface


2. Thallus foliose or much branched pinnately to subdichotomously; tetrasporangia developed by transformation or lateral divisions of inward-growing clusters of secondary filaments in the mid medulla; tetrasporangial sori small, maculate, located in the medulla; tetraspores released by gelatinous extrusion through a central pore (ie. "non-erosive" sorus)


2. Thallus much branched subdichotomously to laterally or radially; tetrasporangia developed by transformation of or by lateral divisions of inner cortical or outer medullary cells; tetrasporangial sori in surface view irregular to elliptical or linear, located at the boundary between inner cortex and medulla; tetraspores released by excision and gelatinous extrusion of the sorus (ie. "erosive" sorus)


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