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Phylum Rhodophyta – Class Florideophyceae – Order Gracilariales

Thallus parasitic on Gelidiaceae or Gracilaria, forming small, white to pigmented, hemispherical to verrucose, pustules. Structure of branched, endophytic, rhizoidal filaments pit-connected to host cells, and the pustules of outer, anticlinal, cortical chains and inner larger-celled, multinucleate, medullary cells with numerous secondary pit-connections.

Reproduction: Gametangial thalli dioecious. Carpogonial branches 2-celled, borne on a supporting cell in a cortical filament, with a straight trichogyne. Auxiliary cells absent; fertilized carpogonium possibly fusing with adjacent vegetative cells and developing the gonimoblast directly, consisting of horizontal filaments fusing with vegetative cells and clusters of erect filaments bearing chains of carposporangia, interspersed among cortical filaments; pericarp absent. Spermatangia formed in chains from surface cortical cells, cut off by intercalary divisions from initial cells.

Tetrasporangia scattered in the cortex or in pits, cruciately or zonately divided.

Life history triphasic with essentially isomorphic gametophytes and tetrasporophyte.

Taxonomic notes: A family of 3 minute parasitic genera (Pterocladiophila Fan & Papenfuss and Gelidiocolax Gardner on Gelidiaceae and Holmsella Sturch on Gracilaria) which Fredericq & Hommersand (1990a) place in the Gracilariales. Only Holmsella has been recorded from southern Australia.


FAN, K.-C. & PAPENFUSS, G.F. (1959). Red algal parasites occurring on members of the Gélidiales. Madroilo 15, 33–38.

FREDERICQ, S. & HOMMERSAND, M.H. (1990a). Morphology and systematics of Holmsella pachyderma (Pterocladiophilaceae, Gracilariales). Br. phycol. J. 25, 39–51.

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

Author: H.B.S. Womersley

Publication: Womersley, H.B.S. (28 June, 1996)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIIB. Gracilarialse, Rhodymeniales, Corallinales and Bonnemaisoniales
Reproduced with permission from The Marine Benthic Flora of Southern Australia Part IIIB 1996, by H.B.S. Womersley. Australian Biological Resources Study, Canberra. Copyright Commonwealth of Australia.

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