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Electronic Flora of South Australia Genus Fact Sheet

Genus VIDALIA Lamouroux ex J. Agardh 1863: 1117, nom. cons.

Phylum Rhodophyta – Family Rhodomelaceae – Tribe Amansieae

Thallus erect, much branched irregularly from the margin, branches flat and complanate or spirally twisted, usually 2–5 mm broad, with alternate marginal serrations; surface of branches smooth, without proliferous outgrowths apart from reproductive structures; branches with a midrib and inconspicuous veins to the serrations. Structure. Apices revolute, axial filament with 5 pericentral cells, 2 lateral ones on each side and a ventral pericentral cell, together with a pseudopericentral cell cut off each of the dorsal lateral pericentral cells and sometimes a further pseudopericentral from the ventral pericentral cell. Thallus 2 medullary cells and 1–3 cortical cells thick, the midrib thickened by cortical cell proliferation. Trichoblasts present on marginal serrations and over the midrib.

Reproduction: Reproductive organs borne over the branch midrib or on the serrations. Procarps unknown. Carposporophytes with a basal fusion cell, branched gonimoblast and clavate terminal carposporangia. Cystocarps globular, stalked; pericarp ostiolate, several cells thick. Spermatangial organs borne on trichoblasts, subspherical to ovoid.

Tetrasporangial stichidia clustered on the midrib, elongate-ovoid to fusiform, compressed, with 2 rows of tetrasporangia, corticated.

Lectotype: V. spiralis (Lamouroux) Lamouroux ex J. Agardh 1863: 1126 (Schmitz 1889: 447).

Taxonomic notes: A genus of about 9 species (see Norris 1991) here separated from the single species of Osmundaria.

Norris (1991) considered that Vidalia was a synonym of Osmundaria, based on study of the proliferous basal lateral shoots previously named by Falkenberg as Vidalia gregaria, agreeing with Harvey (1862a, pl. 188) who had considered them only young stages of the supposed host. Harvey and Norris are almost certainly correct, as is further supported by occasional small proliferous laterals (e.g. on AD, A69013) being partly bare and partly with surface proliferations (e.g. on one side only, or near the base only), the lack of any reproductive structures on the proliferations, and sections of the base of the proliferations on the heavily thickened Osmundaria base appearing to show that they involve only outgrowth from the thickened cortex.

However, this does not support union of Vidalia with Osmundaria, and based on the type species of both genera they differ as follows:

1. In habit, Vidalia having prominent alternate marginal dentations which Osmundaria lacks.

2. Vidalia having a smooth surface, Osmundaria branches being covered by abundant short, branched, spinous proliferations.

3. Vidalia having an alternate, lateral vein system leading to the marginal dentations, with the lateral pericentral cells not forming rows across the thallus as in Osmundaria which in general does not show such a lateral vein system.

4. Reproductive organs in Vidalia are borne centrally on the branches, above the midrib, in contrast to Osmundaria where they are marginal.

As well as the type species, Vidalia includes V. intermedia J. Agardh (1890, p. 69) from the central coast of Western Australia, which differs from V. spiralis in not being spirally twisted; its relationships with V. spiralis need further study.

Vidalia cliftonii Harvey 1863, synop.: xvi; De Toni 1903: 1107; Lucas 1909: 46. May 1965: 398; Sonder 1880: 32, transferred to Osmundaria spiralis as var. clifionii (Harvey) Norris (1991: 20, fig. 23-fig. not this var.), followed by Silva et al. (1996, p. 533) has no relationship to V. spiralis, having 4 pericentral cells and an ecorticate thallus 2 cells thick. Until its reproduction is known, its relationships cannot be established, but it is probably generically distinct from Vidalia.


AGARDH, J.G. (1863). Species Genera et Ordines Algarum. Vol. 2, Part 3, pp. 787–1291. (Gleerup: Lund.)

AGARDH, J.G. (1890). Till algernes systematik. Acta Univ. lund. 26(3), 1–125, Plates 1–3.

DE TONI, G.B. (1903). Sylloge Algarum omnium hucusque Cognitarum. Vol. 4. Florideae. Sect. 3. pp. 775–1521 + 1523–1525. (Padua.)

HARVEY, W.H. (1862a). Phycologia Australica. Vol. 4, Plates 181–240. (Reeve: London.)

HARVEY, W.H. (1863). Phycologia Australica. Vol. 5, Plates 241–300, synop., pp. i-lxxiii. (Reeve: London.)

LUCAS, A.H.S. (1909). Revised list of the Fucoideae and Florideae of Australia. Proc. Linn. Soc. N.S.W. 34, 9–60.

MAY, V. (1965). A census and key to the species of Rhodophyceae (red algae) recorded from Australia. Contr. N.S. W. Natl Herb. 3, 349–429.

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

SCHMITZ, F. (1889). Systematische Übersicht der bisher bekannten Gattungen der Florideen. Flora, Jena 72, 435–456, Plate 21.

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

SONDER, O.W. (1880). In Mueller, F., Fragmenta Phytographiae Australiae. Supplementum ad volumen undecinum: Algae Australianae hactenus cognitae, pp. 1–42, 105–107. (Melbourne.)

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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