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Electronic Flora of South Australia Genus Fact Sheet

Genus COELARTHRUM Bogesen 1910: 192

Phylum Rhodophyta – Class Florideophyceae – Order Rhodymeniales – Family Rhodymeniaceae

Thallus erect or decumbent, irregularly or regularly and synchronously branched, with or without percurrent axes, constricted with ovoid to elongate, hollow, mucilage-filled segments. Structure multiaxial, segments with a thin cortex with usually a single layer of outer cells, and a large-celled medulla 1–2 cells broad, bearing secretory cells on smaller inner cells or filaments; partitions one or many cells thick.

Reproduction: Gametangial thalli dioecious. Carpogonial branches 4-celled, borne on mid cortical supporting cells, auxiliary cells borne on an intercalary cortical cell on the supporting cell. Carposporophytes erect with a basal fusion cell and gonimoblast cells all becoming carposporangia. Basal nutritive tissue present, with erect filaments disintegrating early. Cystocarps protruding, with a thick pericarp, ostiolate. Spermatangia in sari, cut off from outer cortical cells.

Tetrasporangia scattered, transformed from inner cortical intercalary cells, decussately divided.

Life history triphasic, with isomorphic gametophytes and tetrasporophytes.

Type species: C. albertisii (Piccone) Børgesen 1910: 192, figs 11, 12.

Taxonomic notes: A genus of about six species, characterised by the hollow segments, external cystocarps without persistent erect filaments around the carposporophyte, and scattered tetrasporangia transformed from inner cortical cells. The Australian species have been monographed by Huisman (1996).


BØRGESEN, F. (1910). Some new or little known West Indian Florideae. II. Bot. Tidsskr. 30, 179–207.

HUISMAN, J.M. (1996). The red algal genus Coelarthrum. Børgesen (Rhodymeniaceae, Rhodyméniales) in Australian waters. Phycologia 35, 95–112.

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

Author: H.B.S. Womersley

Publication: Womersley, H.B.S. (28 June, 1996)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIIB. Gracilarialse, Rhodymeniales, Corallinales and Bonnemaisoniales
Reproduced with permission from The Marine Benthic Flora of Southern Australia Part IIIB 1996, by H.B.S. Womersley. Australian Biological Resources Study, Canberra. Copyright Commonwealth of Australia.


1. Thallus even-topped, with segments branched apically, growth largely synchronous; constrictions 0.5–1 mm long, with pseudoparenchymatous, relatively thick, partitions

C. opuntia

1. Thallus irregularly branched with percurrent main axes and branches, new branches arising from any part of the upper half of segments; constrictions very short, partitions monostromatic

C. cliftonii

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