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Genus INTERTHAMNION Gordon 1972: 135

Phylum Rhodophyta – Order Ceramiales – Family Ceramiaceae – Tribe Spermothamnieae

Thallus with prostrate filaments bearing erect, branched filaments 1–2 mm high, prostrate filaments attached by digitate haptera; cortication absent; cells uninucleate.

Reproduction: Gametophytes dioecious. Female axes terminal on erect axes with the last two cells small and the hypogenous cell larger. Procarp on the subapical cell, with 3 periaxial cells, one sterile, one fertile (with an auxiliary cell) and the supporting cell with a terminal sterile cell and a lateral carpogonial branch. Auxiliary cells 2 per procarp, each producing a gonimolobe with terminal carposporangia. Sterile procarp cells producing post-fertilization 3 small groups of 3–5 cells each; hypogenous cell producing post-fertilization 4 outer involucral branchlets. Spermatangial heads ovoid, sessile, usually unilateral and adaxial on erect axes.

Tetrasporangia pedicellate, on clustered branchlets lateral on erect axes, with small involucral branchlets, tetrahedrally divided.

Type (and only) species: I. attenuatum Gordon 1972: 137, fig. 44.

Taxonomic notes: Interthamnion is most closely related to Spermothamnion, differing in having a relatively elongate hypogenous cell producing 4 post-fertilization laterals, and without a distinct fusion cell; Spermothamnion also has no division of the sterile cells of the procarp.


GORDON, E.M. (1972). Comparative morphology and taxonomy of the Wrangelieae, Sphondylothamnieae and Spermothamnieae (Ceramiaceae, Rhodophyta). Aust. J. Bot. suppl. 4, 1–180.

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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