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Electronic Flora of South Australia Genus Fact Sheet

Genus LEATHESIA Gray 1821: 301

Phylum Phaeophyta – Order Chordariales – Family Leathesiaceae

Thallus 5–50 (–80) mm across, applanate to lobed or globose, mucoid but firm, often becoming hollow, epilithic or epiphytic. Basal layer of radiating filaments of isodiametric cells with marginal growth. Medulla extensive, of irregularly shaped cells developing anastomoses with laterally adjacent cells and with lacunae between them. Determinate cortical filaments arising from upper medullary cells, forming a short, compact stratum of even height, 3–10 cells long with the terminal cell globose and distinctly larger than the sub-terminal cell. Phaeoplasts several per cell, with or without a pyrenoid. Phaeophycean hairs arising from upper medullary cells, scattered but often in small clusters.

Reproduction: Plurilocular sporangia solitary or in small corymbose groups, arising from subcortical cells, uniseriate. Unilocular sporangia borne on basal cells of determinate cortical filaments, ovoid to subglobose.

Life history diplohaplontic and heteromorphic, with or without a filamentous gametophyte (see Dangeard 1969).

Type species: L. tuberiformis (Smith) Gray [= L. difformis (L.) Areschoug].

Taxonomic notes: A genus of about 11 species, mainly in the North Pacific and Australasia, but with the type species widespread in cool temperate parts of the world. Inagaki (1958) credits 9 species to Japan but not all these show the anastomosing of medullary filaments and one does not have the enlarged, terminal cell of the cortical filaments, which are here considered distinctive of Leathesia. Ajisaka (1984) found that the diploid or haploid macrothallus of L. japonica alternates with a haploid filamentous microthallus similar to Polytretus reinboldii at temperatures less than 10C, but without evidence of sexual fusion.


AJISAKA, T. (1984). The life history of Leathesia japonica Inagaki (Phaeophyta, Chordariales) in culture. Jap. J. Phycol. 32, 234–242.

DANGEARD, P. (1969). A propos des travaux récents sur le cycle evolutif de quelques Phéophycées, Phéosporées. Botaniste 52, 59–102.

GRAY, S.F. (1821). A natural arrangement of British Plants. Vol. 1. (London.)

INAGAKI, K. (1958). A systematic study of the order Chordariales from Japan and its vicinity. Sci. Pap. Inst. Algol. Res. Hokkaido Univ. 4, 87–197, Plates I-XI.

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

Author: H.B.S. Womersley & S. Skinner

Publication: Womersley, H.B.S. (14 December, 1987)
The Marine Benthic Flora of Southern Australia
Part II
©Board of the Botanic Gardens and State Herbarium, Government of South Australia


1. Determinate cortical filaments 3–5 (–6) cells long, terminal cell 1.5–2 times the diameter of lower cells; medullary cells ovoid but developing frequent anastomoses and becoming stellate

L. difformis

1. Determinate cortical filaments 4–8(4 0) cells long, terminal cell 4–6 times the diameter of lower cells; medullary cells ovoid, compact, with occasional anastomoses but without developing arms

L. intermedia

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