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Electronic Flora of South Australia Genus Fact Sheet

Genus GRACILARIA Greville 1830: liv, 121

Phylum Rhodophyta – Class Florideophyceae – Order Gracilariales – Family Gracilariaceae

Thallus erect or decumbent, usually much branched subdichotomously, laterally, secundly or irregularly, radially or complanately, branches terete to flattened; holdfast usually discoid, epilithic or in sandy mud or occasionally loose lying. Structure uniaxial but appearing multiaxial, pseudoparenchymatous with a small-celled cortex grading or changing abruptly to a large-celled medulla, cells usually with numerous pit-connections.

Reproduction: Gametangial thalli monoecious or dioecious. Carpogonial branches 2-celled, borne on an inner cortical (supporting) cell which also bears two adjacent filaments, the fertilized carpogonium fusing with cells of these filaments to form a fusion cell producing a dense gonimoblast of ovoid to elongate cells with clusters or chains of terminal carposporangia; traversing nutritive cells or filaments from gonimoblast to upper and/or lower pericarp usually present, either as single elongate cells or involving also several, fused, inner stellate cells of the pericarp. Cystocarps prominent, sessile and hemispherical to globular and basally constricted, with a thick pericarp, ostiolate; in some species an inner pericarp occurs by cell proliferation at the base of the carposporophyte. Spermatangia formed in pits or cavities, cut off from basal cells or cells of branched filaments lining the cavities.

Tetrasporangia scattered in the outer (often slightly thickened) cortex, basally pit-connected, cruciately divided.

Life history triphasic with isomorphic gametophytes and tetrasporophytes.

Type: Suggested lectotype species: G. compressa (C. Agardh) Greville 1830: 125 [= G. bursa-pastoris (S. Gmelin) Silva 1952: 265] - see Steentoft, Irvine & Bird 1991: 663.

Taxonomic notes: The previously accepted lectotype species of Gracilaria, G. confervoides (Stackhouse) Greville (1830: liv, 121), has been shown by Steentoft et al. (1991, p. 663) to be, on the basis of the type specimen, a species of Gracilariopsis. To obviate numerous name changes in an economically important genus, they suggest that G. compressa (C. Agardh) Greville should be considered the lectotype species. They also show that synonymy of G. confervoides with G. verrucosa (Hudson) Papenfuss (1950, p. 195) is incorrect, and Irvine & Steentoft (1995) propose rejection of the name Fucus verrucosus. There now appears no reason to record G. verrucosa from southern Australia, and this taxon is probably confined to European coasts.

Much of the confusion between Gracilaria and Gracilariopsis Dawson has been clarified by Fredericq & Hommersand (1989b) who show that the latter genus is characterised by superficial spermatangial sori, absence of traversing nutritive cells from the gonimoblast to the pericarp, and a fertile layer of carposporangia in relatively straight chains. Steentoft et al. (1995) clarify the relationships of the two terete species (Gracilaria gracilis and Gracilariopsis longissima) in Britain.

There is still considerable doubt concerning many species of Gracilaria [see papers in Abbott & Norris (1985), and Abbott (1988, 1992)1, and further studies are needed on the species described below. Australian species were described by May (1948) before modern classification concepts developed, and all her specimens need re-interpretation. Some species have been monographed recently by Withell et al. (1994). Identifications (e.g. as G. confervoides) based on non-sexual collections (where the male is essential) are usually dubious, and as far as possible the collections cited below include male plants. There is also doubt as to identification of some plants from Victorian and Tasmanian coasts which have secund branching. These are mostly interpreted as secund forms of G. ramulosa since they are distinctly less robust with thinner branches than the N.S.W. G. secundata.


ABBOTT, I.A. & NORRIS, J.M. (Eds) (1985). Taxonomy of Economic Seaweeds. With reference to some Pacific and Caribbean species. (Calif. Sea Grant College Program: La Jolla.)

ABBOTT, I.A. (Ed.) (1988). Taxonomy of Economic Seaweeds. With reference to some Pacific and Caribbean species. Vol. II. (Calif. Sea Grant College Program: La Jolla.)

ABBOTT, I.A. (Ed.) (1992). Taxonomy of Economic Seaweeds. With reference to some Pacific and Western Atlantic species. Vol. III. (Calif. Sea Grant College: La Jolla.)

FREDERICQ, S. & HOMMERSAND, M.H. (1989b). Comparative morphology and taxonomic status of Gracilariopsis (Gracilariales, Rhodophyta). J. Phycol. 25, 228–241.

GREVILLE, R.K. (1830). Algae Britannicae. (Maclachlan & Stewart: Edinburgh.)

IRVINE, L.M. & STEENTOFT, M. (1995). Proposal to reject the name Fucus verrucosus Huds. (Rhodophyta). Taxon 44, 223–224.

MAY, V. (1948). The algal genus Gracilaria in Australia. C.S.I.R.O. Bull. 235. pp. 1–64, Plates 1–15.

PAPENFUSS, G.F. (1950). Review of the genera of algae described by Stackhouse. Hydrobiologia 2, 181–208.

SILVA, P.C. (1952). A review of nomenclatural conservation in the algae from the point of view of the type method. Univ. Calif Pubis Bot. 25, 241–324.

STEENTOFT, M., IRVINE, L.M. & BIRD, C.J. (1991). Proposal to conserve the type of Gracilaria, nom. cons., as G. compressa and its lectotypification (Rhodophyta: Gracilariaceae). Taxon 40, 663–666.

STEENTOFT, M., IRVINE, L.M. & FARNHAM, W.F. (1995). Two terete species of Gracilaria and Gracilariopsis (Gracilariales, Rhodophyta) in Britain. Phycologia 34, 113–127.

WITHELL, A.F., MILLAR, A.J.K. & KRAFT, G.T. (1994). Taxonomic studies of Gracilaria (Gracilariales, Rhodophyta) from Australia. Aust. Syst. Bot. 7, 281–352.

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 complanately branched, branches compressed, 2–4 (–5) mm broad

G. preissiana

1. Thallus irregularly to subdichotomously or secundly branched, branches terete, mostly 0.5–2 (–3.5) mm in diameter


2. Thallus 5–25 cm high, densely tufted, branching subdichotomous or somewhat secund, most branches of similar height

G. ramulosa

2. Thallus 10–60 cm high, branching irregular or secund, dense to relatively sparse with long main branches and laterals of varying length


3. Branches with markedly secund laterals, mostly relatively short

G. secundata

3. Branching irregular, with long laterals


4. Thallus slender, apical cell visible, branches 0.4–1 mm in diameter, cortex not thickened on lower branches; spermatangial pits shallow with basal spermatangia ("textorii" type) and with clavate outer cortical cells surrounding

G. chilensis them

4. Thallus robust, apical cell not visible, most branches (1–) 2–3.5 mm in diameter, cortex thickened or not near base; spermatangial pits ovoid ("verrucosa" type) to deeply sunken ("polycavernosa" type)


5. Thallus branches 1–3.5 mm in diameter, thicker near the base where the cortex is thickened; medulla (15–) 20–30 cells broad

G. flagelliformis

5. Thallus branches 1.3–1.8 mm in diameter from base to upper parts, cortex not thickened below; medulla 4–8 cells across, inner cells 150–400 µm in diameter

G. sp.

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