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Phylum Rhodophyta – Class Florideophyceae – Order Gigartinales

Thallus usually erect, branched, terete or compressed, often soft and mucoid, uniaxial with 4 (–6) periaxial cells or multiaxial, with a lax or usually a compact cortex and a medulla with filaments of slender or swollen cells and usually with additional descending rhizoids. Cortical cells larger inwardly, outermost cells often bearing hairs; rhodoplasts discoid.

Reproduction: Sexual thalli dioecious, in some taxa monoecious, non-procarpic. Female gametophyte with carpogonial branches and auxiliary cell branches on separate and often distant periaxial or medullary cells, both of numerous cells and unbranched or bearing short laterals. Carpogonial branches usually reflexed over the terminal 3–4 cells, with several larger cells below; fertilized carpogonium dividing or not, usually connecting to a lower nutritive cell in the carpogonial branch, with the carpogonium or the lower cell developing connecting filaments to auxiliary cells, but in some genera (with non-functional auxiliary cells) producing gonimoblast cells directly. Auxiliary cell branches straight or curved, with or without short laterals, with the auxiliary cell terminal or intercalary and usually smaller than adjacent cells. Carposporophytes developing from the auxiliary cell or adjacent connecting filament, remaining attached to the auxiliary cell branches, with radiating gonimoblast filaments and all cells becoming carposporangia apart from the basal fusion cell, situated within the inner cortex or outer medulla with the adjacent cortex swollen or not. Spermatangia cut off from outer cortical cells, scattered or in groups.

Life history triphasic with gametophyte and tetrasporophyte isomorphic, or heteromorphic with the tetrasporophyte prostrate and usually crustose.

Taxonomic notes: Tetrasporophytes similar to gametophytes or prostrate and usually crustose.

Tetrasporangia zonately or cruciately divided, often irregularly divided in crustose
sporophytes, produced from cortical cells.

A family of some 16 genera (Kylin 1956, p.148; Shepley & Womersley 1983; Kraft 1986), three of which have been placed in the segregate family Weeksiaceae (Abbott 1968). The reproductive features have been reviewed by Lindstrom (1984) who (Lindstrom 1987) has also established a separate family for Acrosymphyton. The largest number of genera (8) occur on Pacific North American coasts (Abbott & Hollenberg 1976, pp. 354–368, including Weeksiaceae), and the family is apparently only known in the southern hemisphere from Australia, apart from Leptocladia peruviana Howe (1914, p. 176) from northern Peru. The southern Australian species have been described by Mitchell (1966) and Shepley & Womersley (1983), and the type and Australian species of Dudresnaya by Robins & Kraft (1985).


ABBOTT, I.A. & HOLLENBERG, G.J. (1976). Marine Algae of California. (Stanford Univ. Press: Stanford.)

ABBOTT, I.A. (1968). Studies in some foliose red algae of the Pacific Coast. III. Dumontiaceae, Weeksiaceae, Kallymeniaceae. J. Phycol. 4, 180–198.

BORY DE ST-VINCENT, J.B. (1828). In Duperrey, L.I., Voyage autour du monde, exécuté par ordre du Roi, sur la corvette de Sa Majesté, la Coquille, pendant les années 1822, 1823, 1824 et 1825. Botanique, Cryptogamie, pp. 1–300, Plates 1–39. (Bertrand: Paris.)

HOWE, M.A. (1914). The marine algae of Peru. Mem. Torrey Bot. Club 15, 1–185, Plates 1–66.

KRAFT, G.T. (1986). The genus Gibsmithia (Dumontiaceae, Rhodophyta) in Australia. Phycologia 25, 423–447.

KYLIN, H. (1956). Die Gattungen der Rhodophyceen. (Gleerups: Lund.)

LINDSTROM, S.C. (1984). Neodilsea natashae sp. nov. (Dumontiaceae, Rhodophyta) with comments on the family. Phycologia 23, 29–37.

LINDSTROM, S.C. (1987). Acrosymphytaceae, a new family in the order Gigartinales sensu lato (Rhodophyta). Taxon 36, 50–53.

MITCHELL, E.A. (1966). The southern Australian genera of the Dumontiaceae (Rhodophyta). Nova Hedwigia 11, 209–220, Plates 22–26:2.

ROBINS, P.A. & KRAFT, G.T. (1985). Morphology of the type and Australian species of Dttdresnaya (Dumontiaceae, Rhodophyta). Phycologia 24, 1–34.

SHEPLEY, E.A. & WOMERSLEY, H.B.S. (1983). The Dumontiaceae (Cryptonemiales: Rhodophyta) of southern Australia. Trans. R. Soc. S. Aust. 107, 201–217.

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 irregularly laterally branched, uniaxial with prominent axial cells bearing whorls of periaxial cells


1. Thallus subdichotomously to irregularly furcately branched, multiaxial


2. Carpogonial branches bearing short lateral branches, with fusion between the fertilized carpogonium and cells of these laterals; auxiliary cell terminal on auxiliary cell branch; heteromorphic with a prostrate, filamentous tetrasporophyte (unknown in A. taylorii)


2. Carpogonial branches generally without laterals, fertilized carpogonium fusing with cell(s) 3–5 of the branch; auxiliary cell intercalary in auxiliary cell branch; isomorphic gametophytes and tetrasporophytes


3. Cortex compact; persistent, acicular, unicellular hairs present on outer cortical cells; carposporophytes in small numbers, each causing localized swelling of the thallus


3. Cortex lax; acicular unicellular hairs not present on outer cortical cells; carposporophytes numerous, scattered, not causing swelling of thallus


4. Thallus epiphytic on Amphibolis, 1–3 cm high, subdichotomous; outer cortical cells bearing thick-walled hyaline hairs; lateral connections between filaments absent; tetrasporophyte crustose


4. Thallus epilithic (or on jetty piles), with a basal stalk and irregularly furcate branches (3–) 10–48 cm long, outer cortical cells without thick-walled hyaline hairs; lateral connections between cortical and medullary filaments present; generations isomorphic, tetrasporangia cruciately divided


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