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Electronic Flora of South Australia Genus Fact Sheet

Genus RHIPIDOTHAMNION Huisman 1985: 55

Phylum Rhodophyta – Order Ceramiales – Family Ceramiaceae – Tribe Spermothamnieae

Thallus with prostrate filaments bearing erect, unilaterally and secundly branched erect filaments, prostrate filaments attached by digitate haptera; cortication absent; cells multinucleate.

Reproduction: Gametophytes dioecious. Female axes terminal, displaced laterally, with 2 small cells and a larger hypogenous cell. Sub-apical cell bearing two sterile periaxial cells and a supporting cell with a sterile cell and a lateral carpogonial branch. Post-fertilization a connecting cell occurs between the carpogonium and auxiliary cell, and a fusion cell develops with gonimolobes bearing terminal carposporangia. Sterile cells of the procarp produce 4, -branched, inner involucral filaments which loosely surround the gonimoblast. No outer involucre develops. Spermatangial heads ovoid, sessile, adaxial on each cell of curved branches, with 4–7 axial cells each cutting off 2–3 periaxial cells which, directly or via further initials, each produce 2–4 spermatangia.

Tetrasporangia borne adaxially on cells of curved branches, 1–3 per cell, sessile, tetrahedrally divided.

Type (and only) species: R. secundum Huisman 1985: 56, figs 2–15.

Taxonomic notes: Rhipidothamnion is distinguished by formation only of inner involucral branchlets from sterile cells of the procarp, with no outer involucral branchlets, and differs from the only other genus with these features (Lejolisia) in that the branchlets are loosely arranged and not in the form of a pericarp within a gelatinous sheath.


HUISMAN, J.M. (1985). Rhipidothamnion secundum gen. et sp. nov. and Spermothamnion miniatum sp. nov. (Ceramiaceae, Rhodophyta) from eastern Australia. Phycologia 24, 55–66.

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

Author: H.B.S. Womersley

Publication: Womersley, H.B.S. (24 December, 1998)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIIC. Ceramiales – Ceramiaceae, Dasyaceae
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