Electronic Flora of South Australia Genus Fact Sheet

Genus LEPTOSOMIA (J. Agardh) J. Agardh 1892: 86

Phylum Rhodophyta – Class Florideophyceae – Order Rhodymeniales – Family Rhodymeniaceae

Thallus foliose, usually with marginal lobes, delicate, soft and mucilaginous, holdfast discoid or enveloping host stems. Structure multiaxial, with a cortex 1–2 cells thick and a medulla of large ovoid cells on either side of a central space within which coarse rhizoids develop, completely filling the space in older parts.

Reproduction: Gametangial thalli dioecious. Carpogonial branches 3-celled, borne on inner cortical cells, with the 2-celled auxiliary cell branch. Carposporophyte erect, with a branched basal fusion cell and all gonimoblast cells becoming carposporangia. Basal nutritive tissue concave, of short cells, with few, inconspicuous or disintegrating erect filaments. Cystocarps scattered, largely immersed in the thallus, with a surface pericarp of small-celled filaments, ostiolate. Spermatangia cut off via initials from surface cortical cells.

Tetrasporangia scattered, transformed from inner cortical cells, intercalary and pit-connected to outer cortical cells, cruciately divided.

Life history triphasic with isomorphic gametophytes and tetrasporophytes.

Type species: L. cliftonii (J. Agardh) J. Agardh 1892: 88 [= L. rosea (Harvey) Womersley, comb. nov.].

Taxonomic notes: Leptosomia was first described by J. Agardh (1876, p. 319) as a subgenus of Chrysymenia, doubtfully including two other species. Later J. Agardh (1892, p. 86) elevated Leptosomia to a genus. Kylin (1956, p. 336), followed by Papenfuss (1964, p. 44) and Etcheverry (1986, p. 283) placed four Antarctic species of Leptosarca Gepp & Gepp under Leptosomia but Leptosarca is now regarded as a synonym of Palmaria.

The genus is characterised by its vegetative structure, with a central space between large medullary cells, within which rhizoids develop, at first sparse but in older parts filling the space completely. Leptosomia is probably monotypic.

References:

AGARDH, J.G. (1876). Species Genera et Ordines Algarum. Vol. 3, Part 1 — Epicrisis systematis Floridearum, pp. i-vii, 1–724. (Weigel: Leipzig.)

AGARDH, J.G. (1892). Analecta Algologica. Acta Univ. lund. 28, 1–182, Plates 1–3.

ETCHEVERRY, D.H. (1986). Algas Marinas Bentónicas de Chile. (Unesco: Montevideo.)

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

PAPENFUSS, G.F. (1964). Catalogue and bibliography of antarctic and subantarctic benthic marine algae. Am. geophys. Un. Antarctic Res. Ser., 1, 1–76.

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.

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