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Genus HALYDICTYON Zanardini 1843: 52

Phylum Rhodophyta – Family Rhodomelaceae – Tribe Uncertain

Thallus forming an irregularly expanding network, vaguely lobed or branched; usually epiphytic, attached by short processes. Structure. Growth from surface areas of small meristematic cells regularly arranged, forming square or polygonal cell meshes by union of lateral cells at the join of adjacent branches; cells expanding in size but not dividing below the meristematic surface area. Cells multinucleate.

Reproduction: Gametophytes monoecious (Coppejans 1975), female plants rare. Procarps borne on upper filaments, developing 4 pericentral cells, with a carpogonial branch. Cystocarps ovoid to urceolate, pericarp ecorticate. Spermatangial organs compressed, ovate, with sterile basal cell and marginal cells, the axial cells cutting off lateral pericentral cells which produce the sterile marginal cells and transverse cells which form plates of smaller cells which produce spermatangia.

Tetrasporangial stichidia compressed, ovate-pointed to elongate, with opposite tetrasporangia. Axial cells with 4 pericentral cells, the transverse ones remaining undivided and the lateral ones cutting off marginal cells and a lateral cell on each side of the stichidium, then a tetrasporangium upwards; tetrasporangia subspherical, tetrahedrally divided.

Type species: H. mirabile Zanardini 1860: 17.

Taxonomic notes: A genus of 3 or 4 species, one from southern Australia and H. australe (Sonder) Harvey (1859a, pl. 91), distinguished by its habit, the meshes forming branched terete fronds 4–6 mm broad and 5–15 cm high, occurring on the West Australian coast apparently from Rottnest I. north.

Halydictyon (incorrectly spelt Halodictyon - see Silva 1996, p. 495) is a little-known genus as to its female reproduction and taxonomic relationships; a polysiphonous structure occurs only in the reproductive organs. It has been placed in the Dasyaceae (e.g. Coppejans 1975) or the Rhodomelaceae (e.g. Silva et al. 1996, p. 495). Falkenberg (1901, p. 697) and Børgesen (1930, p. 143) relate it to the Delesseriaceae. From the reproductive organs it appears most likely to be rhodomelaceous but this should be clarified by detailed studies of the female structures and by protein sequencing.


BØRGESEN, F. (1930). Marine algae from the Canary Islands. III. Rhodophyceae. Part III. Ceramiales. K. Dan. Vidensk. Selskab. Biol. Medd. 9, 1–159.

COPPEJANS, E. (1975). Végétation marine de l'île de Port-Cros (Parc National). XI. Sur Halodictyon mirabile Zanard. (Rhodophyceae). Biol. Jb. Dodonaea 43, 116–126.

FALKENBERG, P. (1901). Die Rhodomelaceen des Golfes von Neapel und der angrenzenden Meeres-abschnitte. Fauna und Flora des Golfes von Neapel. Monogr. 26. (Friedländer: Berlin.)

HARVEY, W.H. (1859a). Phycologia Australica. Vol. 2, Plates 61–120. (Reeve: London.)

SILVA, P.C., BASSON, P.W. & MOE, R.L. (1996). Catalogue of the Benthic Marine Algae of the Indian Ocean. (Univ. California Press: Berkeley.)

ZANARDINI, G. (1843). Saggio di classificazione naturale delle Ficee. (Venezia.)

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

Publication: Womersley, H.B.S. (24 February, 2003)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIID. Ceramiales – Delesseriaceae, Sarcomeniaceae, Rhodomelaceae
Reproduced with permission from The Marine Benthic Flora of Southern Australia Part IIID 2003, by H.B.S. Womersley. Australian Biological Resources Study, Canberra. Copyright Commonwealth of Australia.

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