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Electronic Flora of South Australia Genus Fact Sheet

Genus OSMUNDARIA Lamouroux 1813: 42

Phylum Rhodophyta – Family Rhodomelaceae – Tribe Amansieae

Thallus erect, cartilaginous, moderately branched with long, flat, ultimate branches with rounded apices, margins smooth to closely dentate, midrib inconspicuous, lateral veins absent or inconspicuous. Surface of branches covered with a felt of short, branched, multicellular proliferations up to 1 mm long and often with surface sponge, with bare proliferous branches from basal, thickened axes of some plants. Holdfast conical. Structure. Apical cells inconspicuous, axial cells cutting off 5 pericentral cells, 2 lateral on each side and one ventral, with a pseudopericentral cell cut off from each of the dorsal lateral pericentral cells; medulla 1–2 cells broad, cortex 1–3 cells broad, with the lateral pericentral cell derivatives forming horizontal lines across the thallus. Trichoblasts absent.

Reproduction: Procarps borne on short, polysiphonous laterals on marginal shoots near branch apices; carposporophytes with a prominent, branched, basal fusion cell, branched gonimoblast and clavate terminal carposporangia. Cystocarps stalked, ovoid to globular; pericarp with a small ostiole, several cells thick. Spermatangia unknown.

Tetrasporangial stichidia clustered on margins of upper branches, occasionally on the branch surface, elongate, compressed, with rows of 2 tetrasporangia per segment, corticated.

Type species: 0. prolifera Lamouroux 1813: 43.

Taxonomic notes: Osmundaria is a distinctive monospecific genus. Norris (1991) considered Vidalia Lamouroux not distinct from Osmundaria on the basis of the smooth-surfaced proliferous branches from the lower denuded branches, but the dense covering of mature surfaces with short, branched, proliferations and also the lack of alternate, lateral veins in marginal serrations clearly separate the two genera (see under Vidalia). Most if not all the species Norris placed in Osmundaria probably belong in Vidalia.


LAMOUROUX, J.V.F. (1813). Essai sur les genres de la famille des thalassiophytes non articulées. Ann. Mus. Hist. Nat., Paris 20, 21–47, 115–139, 267–293, Plates 7–13.

NORRIS, R.E. (1991). The structure, reproduction and taxonomy of Vidalia and Osmundaria (Rhodophyta, Rhodomelaceae). Bot. J. Linnean Soc. 106, 1–40.

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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