Electronic Flora of South Australia Family Fact Sheet

FAMILY GALAXAURACEAE Parkinson 1983: 608

Phylum Rhodophyta – Class Florideophyceae – Order Nemaliales

Thallus (gametophyte, and sporophyte in some taxa) erect, usually subdichotomous, cylindrical or compressed, multiaxial with a filamentous medulla and filamentous to pseudoparenchymatous cortex, in some taxa becoming hollow; calcified in Galaxaura.

Tetrasporophytes filamentous or crustose, or similar to gametophytes but dimorphic in Galaxaura.

Reproduction: Carpogonial branches 3-celled, with the hypogynous cell and basal cell bearing sterile filaments, those from the latter forming a distinct filamentous involucre; involucre in Galaxaura formed from gonimoblast filaments. Gonimoblast filaments developing from the fertilized carpogonium and producing carposporangia terminally, singly or in short chains; cystocarps within the outer medulla, ostiolate. Spermatangia produced from surface or hypodermal cortical cells, or within conceptacles.

Tetrasporangia cruciately divided, formed terminally or laterally on cortical filaments or on the filamentous or crustose sporophytes.

Life history triphasic and heteromorphic (or dimorphic in Galaxaura).

Taxonomic notes: A family of some 7 genera, characterised by lack of an auxiliary cell and direct development of the gonimoblast from the fertilized carpogonium, and separated from the Helminthocladiaceae by the presence of a well-developed involucre formed either from the sterile filaments on the basal cell of the carpogonial branch, or from the gonimoblast filaments themselves, and an ostiole.

Galaxauraceae was proposed by Parkinson (1983, p. 608) to replace Chaetangiaceae, the type genus of which (Chaetangium Kützing) was based on Fucus ornatus Linnaeus and is a synonym of Suhria J. Agardh ex Endlicher. The species credited to Chaetangium are now referred to Nothogenia Montagne.

References:

PARKINSON, P.G. (1983). The typification and status of the name Chaetangium (algae). Taxon 32, 605–610.

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

Author: 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 GENERA OF GALAXAURACEAE

1. Thallus soft, terete, with a dense slender core of entwined longitudinal medullary filaments producing an outer medulla of radiating filaments and a small-celled cortex, with or without colourless utricles; gonimoblast filaments with chains of carposporangia

2

1. Thallus soft or firm and drying cartilaginous, calcified or not, medulla of slender or coarse filaments but not differentiated into a longitudinal core and outer radiating filaments; cortex of short filaments of slender or larger cells but without utricles; gonimoblast filaments with single terminal carposporangia

3

2. Outer cortical layer entirely or largely formed of colourless, inflated utricles

SCINAIA

2. Outer cortical layers of progressively smaller cells, without colourless inflated utricles

GLOIOPHLOEA

3. Thallus not calcified; medullary and cortical filaments slender; gametophyte erect, tetrasporophyte crustose and discoid

NOTHOGENIA

3. Thallus calcified within the medulla and/or cortex; medullary filaments usually coarse, with a relatively large-celled, often pseudoparenchymatous cortex; gametophyte and tetrasporophyte thalli of similar size but dimorphic in structure, or with a minute filamentous sporophyte

4

4. Innermost cortical cells firmly laterally attached (often fusing in the gametophyte), remaining attached after decalcification; cystocarp without a sterile involucre, the wall being formed from gonimoblast filaments; tetrasporophyte and gametophyte of similar size but dimorphic

GALAXAURA

4. Cortical cells not laterally attached, separable into filaments after decalcification; cystocarp with a sterile involucre arising from the basal cell of the carpogonial branch; tetrasporophyte minute, filamentous

TRICLEOCARPA


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