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Phylum Rhodophyta – Class Florideophyceae – Order Gigartinales

Thallus erect, foliose, subdichotomous and compressed, or irregularly branched with terete branches, soft or cartilaginous. Structure usually multiaxial (uniaxial in Antrocentrum), developing a filamentous medulla and pseudoparenchymatous cortex.

Reproduction: Sexual thalli monoecious; procarpic. Carpogonial branches 2- or 3-celled, borne on inner cortical supporting cells, inwardly directed with reflexed trichogynes; connecting filaments absent. Supporting cells functioning as auxiliary cells, following union with fertilized carpogonia producing several gonimoblast initials which enter an adjacent region of nutritive cells, developing thallus inwardly (except Amphiplexia); fusion cells absent. Gonimoblast filaments connecting with nutritive enveloping tissue cells and lining a cavity formed by breakdown of the auxiliary cell, giving rise to carposporangial filaments radiating inwards from the cystocarp wall and bearing terminal, or short chains of, carposporangia, released through a more or less defined ostiole. Spermatangia in scattered ampulliform clusters in the outer cortex.

Tetrasporangia scattered in the cortex or in nemathecia, basally attached, zonately divided.

A family of 7 genera and 8 species, largely southern Australian (5 genera and 6 species), monographed by Kraft (1977a) and Kraft & Min-Thein (1983). The family, considered highly specialised by Kraft, is characterised by the filamentous medulla, inwardly directed carpogonial branches, the supporting cell becoming the auxiliary cell, lack of a fusion cell, and the cystocarp with gonimoblast filaments radiating inwardly from the wall, together with zonately divided tetrasporangia.

Life history triphasic with isomorphic gametophytes and tetrasporophytes.


KRAFT, G.T. & MIN-THEIN, U. (1983). Claviclonium and Antrocentrum, two new genera of Acrotylaceae (Gigartinales, Rhodophyta) from southern Australia. Phycologia 22, 171–183.

KRAFT, G.T. (1977a). Studies of marine algae in the lesser-known families of the Gigartinales (Rhodophyta). I. The Acrotylaceae. Aust. J. Bot. 25, 97–140.

SCHMITZ, F. (1892). Florideae. In Engler, A., Syllabus der Vorlesungen Ober spezielle und medicinisch-pharmaceutische Botanik. Eine Ubersicht fiber das gesammte Pflanzensystem mit Berticksichtigung der Medicinal-und Nutzpflanzen. Grosse Ausgabe. (Berlin.)

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.


1. Thallus more or less complanately branched with compressed, subdichotomous branches; gonimoblast initials directed thallus inwards


1. Thallus irregularly branched with terete branches or with segmented ramuli borne radially on long main branches; gonimoblast initials thallus directed inwards or outwards


2. Thallus subdichotomous, branches 1–3 mm broad; cortical cells grading evenly in size; polycarpogonial, carpogonial branches 3-celled, cystocarps deeply embedded; tetrasporangia in nemathecia


2. Thallus irregularly subdichotomous, branches 2–10 mm broad; inner cortex with a layer of large isodiametric cells on each side of the filamentous medulla; monocarpogonial, carpogonial branches 2-celled, cystocarps protruding to one side of branch; tetrasporangia scattered in the cortex


3. Thallus of elongate-clavate segments branching from their apices, basally constricted; gonimoblast initials thallus outwards, cystocarps external to branches, carposporangia in chains of 2–3


3. Thallus irregularly branched, branches terete, or with long main branches bearing short laterals of 1–3 segments; gonimoblast initials thallus inwards, cystocarps embedded, carposporangia single


4. Thallus irregularly branched, branches terete and only slightly basally constricted, with uniaxial apices


4. Thallus with long main branches covered irregularly radially with short laterals of 1–3 segments; multiaxial


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