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Electronic Flora of South Australia Genus Fact Sheet

Genus MELANTHALIA Montagne 1843: 296

Phylum Rhodophyta – Class Florideophyceae – Order Gracilariales – Family Gracilariaceae

Thallus erect, 10–40 cm high, cartilaginous, subdichotomously branched, branches linear, compressed, 0.5–4 mm broad, dark red-brown and drying darker to almost black; holdfast discoid. Structure multiaxial, pseudoparenchymatous throughout, cells usually with refractive globules; branch apices with a dome-shaped cap of rows of relatively small, cytoplasm-dense, cells surmounting the core of larger, less dense, medullary cells. Outer cortical cells dividing by obliquely longitudinal divisions followed by transverse division of subapical cells.

Reproduction: Gametangial thalli probably dioecious. Carpogonial branches 2-celled, borne on supporting cells in the mid cortex, probably with adjacent sterile branches. Carposporophyte with a small basal fusion cell, erect, densely tufted, gonimoblast filaments with straight terminal chains of numerous subspherical carposporangia, maturing apically, largely filling the cystocarp cavity. Cystocarps marginal, with a thick pericarp of dense filaments of short cells, ostiolate. Spermatangia probably in surface sori of anticlinal cell rows from outer cortical cells.

Tetrasporangia in shallow and usually inconspicuous nemathecia below branch apices, basally pit-connected to outer cortical cells which also bear a slender 2–3 celled paraphysis, elongate-ovoid to clavate, cruciately divided.

Life history triphasic with isomorphic gametophytes and tetrasporophytes.

Type species: M. obtusata (Labillardière) J. Agardh 1852: 614.

Taxonomic notes: A genus of about 6 species, three from southern Australia, one (M. polydactylis J. Agardh 1885, p. 58) from the NSW coast (Millar 1990, p. 342, fig. 20C–E), and two from New Caledonia (M. vieillardii Kützing 1869, p. 16, pl. 42c, d and M. fastigiata Kützing 1869, p. 16, pl. 44a, b), both of which need further study.

Melanthalia is a distinctive genus with its subdichotomous, linear, compressed branches each with a terminal cap of smaller cells, cystocarps with a very thick ostiolate pericarp and carposporangia borne in long, straight chains, and tetrasporangia borne in nemathecia. M. abscissa (as M. obtusata var. abscissa) has been investigated by Fredericq & Hommersand (1990c).

The three species recognised below are closely similar in their structure and reproduction, differing essentially in branch width and whether compressed or not. While they could be regarded as varieties of one species, virtually all specimens can be separated on these features and it thus seems best to regard them as species.


AGARDH, J.G. (1852). Species Genera et Ordines Algarum. Vol. 2, Part 2, pp. 337–720. (Gleerup: Lund.)

AGARDH, J.G. (1885). Till algernes systematik. VII. Florideae. Acta Univ. lund. 21, 1–120, Plate 1.

FREDERICQ, S. & HOMMERSAND, M.H. (1990c). Taxonomy of Melanthalia obtusata var. abscissa and its placement in the Gracilariales (Rhodophyta). Crypt. Bot. 2, 4–11.

KÜTZING, F.T. (1869). Tabulae Phycologicae. Vol. 19. (Nordhausen.)

MILLAR, A.J.K. (1990). Marine Red Algae of the Coffs Harbour Region, northern New South Wales. Aust. Syst. Bot. 3, 293–593.

MONTAGNE, C. (1843). Quatrième centurie de plantes cellulaires exotiques nouvelles. Ann. Sci. Nat. Sér. 2, Bot. 20, 294–306.

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. Branches (1.5–) 2–3 (–4) mm broad, strongly compressed

M. obtusata

1. Branches 0.3–1.3 mm broad, terete to compressed


2. Branches distinctly compressed, mostly 0.7–1.3 mm broad

M. abscissa

2. Branches terete to slightly compressed, mostly 0.3–0.8 mm broad

M. concinna

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