Electronic Flora of South Australia Genus Fact Sheet

Genus PLATOMA Schousboe ex Schmitz 1894: 627

Phylum Rhodophyta – Class Florideophyceae – Order Gigartinales – Family Nemastomataceae

Thallus erect, subdichotomous with compressed branches to foliose, usually mucilaginous. Structure multiaxial with a cortex of discrete, subdichotomous branch systems, without gland cells, and a medulla of entangled filaments.

Reproduction: Sexual thalli monoecious or dioecious. Carpogonial branches 3-celled, borne on inner cortical (supporting) cells with adjacent, darkly staining, nutritive auxiliary cells. Non-procarpic, with the auxiliary cells also inner cortical cells. Gonimoblast developing outwardly from the auxiliary cell, with all cells of the carposporophyte becoming carposporangia; an obscure pore or gap between the cortical filaments present above the carposporophytes. Spermatangia cut off from outer cortical cells.

Tetrasporophytes unknown.

Life history: Sexual thalli only known.

Type species . P. cyclocolpa (Montagne) Schmitz 1894: 627.

Taxonomic notes: Platoma, with 8 known species, is distributed from the tropics to subarctic waters (Norris & Bucher 1977, p. 155) so the two species described below from southern Australia are the first from the southern hemisphere.

The genus is closely related to Schizymenia, differing in having neither gland cells nor a distinct ostiole above the carposporophyte, but is similar in having cells of the cortical filaments adjacent to the carpogonial branches becoming darkly staining and acting as nutritive auxiliary cells. Platoma differs from Nemastoma and Adelophycus where the gonimoblast develops from the connecting filament and gland cells also occur. The three species placed above in Tsengia differ from Platoma in having isomorphic gametophytes and tetrasporophytes whereas in Platoma tetrasporophytes are unknown.

The Western Australian Nemastoma damaecornis Harvey (1855a, p. 557) needs investigating. It is known from Fremantle and Rottnest I., and has been collected from 3–16 m depths in the Perth region and possibly also from Lord Howe I.

Norris & Bucher (1977, p. 161) discuss the valid publication of the name Platoma, and also conclude that the generic name should be accepted as a feminine noun.

References:

HARVEY, W.H. (1855a). Some account of the marine botany of the colony of Western Australia. Trans. R. Ir. Acad. 22, 525–566.

NORRIS, J.N. & BUCHER, K.E. (1977). The genus Platoma (Gigartinales, Rhodophyta) with a description of P. abbottiana sp. nov. J. Phycol. 13, 155–162.

SCHMITZ, F. (1894). Kleinere Beitrage zur Kenntniss der Florideen. IV. Nuova Notarisia 5, 608–635.

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

Author: by H.B.S. Womersley & G.T. Kraft

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.

KEY TO SPECIES OF PLATOMA

1. Thallus with small marginal lobes; cortex (80–) 120–160 µm thick, branch systems 8–12 cells long, with cortical filaments borne on the supporting cell shorter than normal cortical filaments

P. foliosa

1. Thallus without small marginal lobes; cortex 60–80 µm thick, branch systems 6–8 cells long, with cortical filaments borne on the supporting cell of normal length

P. australica


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