Electronic Flora of South Australia Genus Fact Sheet

Genus GALAXAURA Lamouroux 1812: 185

Phylum Rhodophyta – Class Florideophyceae – Order Nemaliales – Family Galaxauraceae

Thallus erect, 3–25 cm high, much branched more or less subdichotomously, soft to firm, surface superficially smooth to tomentose, with a prominent holdfast and terete, branched, stipes bearing flat or terete and often jointed branches. Structure multiaxial, usually with a slight apical depression, developing a medulla of coarse, branched, filaments and a cortex of relatively large cells often becoming pseudoparenchymatous and 2–3 cells thick, sometimes smooth-surfaced but in most species bearing specialized assimilatory surface cells or filaments; cortex of gametophyte with three layers, the inner 1–2 layers of large colourless cells that often fuse laterally, the remaining layers consisting of progressively smaller and more densely rhodoplastic cells; cortex of tetrasporophyte of two types, either essentially filamentous with or without inflated basal cells supporting assimilatory filaments, or pseudoparenchymatous, of 3–6 layers, the inner cortex of 1–3 layers of large colourless cells, the cells of the outer layer borne on smaller rhodoplastic supporting cells with calcification filling the gaps between the supporting cells. Rhodoplasts stellate, campanulate, with long arms and a central pyrenoid.

Reproduction: Sexual thalli usually dioecious with scattered, ostiolate, male or female conceptacles. Female gametophytes with 3-celled carpogonial branches, with the fertilized carpogonium developing gonimoblast filaments which form the cystocarpic conceptacle and produce centripetally sessile or shortly pedicellate carposporangia; cells on the hypogynous cell appear to be nutritive and do not divide further after fertilization (as in Scinaia), while filaments on the basal cell divide further but do not form an involucre. Male conceptacles with inwardly directed branch systems from peripheral filaments on the conceptacle wall, producing terminal and lateral spermatangia.

The tetrasporophytes with cruciately divided tetrasporangia borne terminally or laterally on the long or the short filaments on the cortex.

Life history triphasic with isomorphic tetrasporophytes and gametophytes (but structurally dimorphic).

Lectotype species: G. rugosa (Ellis & Solander) Lamouroux 1816: 263, designated by Schmitz (1889, p. 439).

Taxonomic notes: Galaxaura is a genus of perhaps 15–20 species, widely distributed in tropical to warm temperate seas, with only one species (G. marginata) widespread along the southern Australian coast and a second species (G. obtusata) found on the south-west coast as far south as Albany. The structural dimorphism and vague habit differences led Kjellman (1900) to recognise some 62 species, but this number has been greatly reduced, especially by Papenfuss et al. (1982) who reviewed the history of the genus and by Huisman & Borowitzka (1990).

References:

HUISMAN, J.M. & BOROWITZKA, M.A. (1990). A revision of the Australian species of Galaxaura (Rhodophyta, Galaxauraceae), with a description of Tricleocarpa gen. nov. Phycologia 29, 150–172.

KJELLMAN, F.R. (1900). Om Floridé-slägtet Galaxaura dess organografi och systematik. K. Svenska Vetensk. Akad. Handl. 33(1), 1–109, Plates 1–20.

LAMOUROUX, J.V.F. (1812). Sur la classification des Polypiers coralligènes non entièrement pierreux. Nouv. Bull. Sci. Soc. Philom. Paris 3, 181–188.

LAMOUROUX, J.V.F. (1816). Histoire des Polypiers Coralligènes Flexibles. (Poisson: Caen.)

PAPENFUSS, G.F., MSHIGENI, K.E. & CHIANG, Y.-M. (1982). Revision of the red algal genus Galaxaura with special reference to the species occurring in the western Indian Ocean. Bot. Mar. 25, 401–444.

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

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

Author: J.M. Huisman & H.B.S. Womersley

Publication: Womersley, H.B.S. (14 January, 1994)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIIA, Bangiophyceae and Florideophyceae (to Gigartinales)
Reproduced with permission from The Marine Benthic Flora of Southern Australia Part IIIA 1994, by H.B.S. Womersley. Australian Biological Resources Study, Canberra. Copyright Commonwealth of Australia.

KEY TO SPECIES OF GALAXAURA

1. Thallus terete throughout, with moniliform branches

G. obtusata

1. Thallus with flattened branches, occasionally arising from a terete stipe

G. marginata


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