Electronic Flora of South Australia Genus Fact Sheet

Genus HALYMENIA C. Agardh 1817: xix

Phylum Rhodophyta – Class Florideophyceae – Order Gigartinales – Family Halymeniaceae

Thallus variously branched, complanate, foliose to bipinnate, soft and mucilaginous, with a discoid holdfast and short stipe. Structure multiaxial, with a relatively narrow cortex 3–6 cells thick, inner cells often stellate, and a lax medulla in young parts with many to most filaments transversely orientated, dense and irregular in older parts; refractive ganglionic cells usually present.

Life history triphasic with isomorphic gametophytes and tetrasporophytes. Reproduction. Sexual thalli dioecious. Carpogonial branch ampullae with several simple secondary filaments converging above. Auxiliary cell ampullae larger, with numerous secondary filaments and often tertiary filaments, often remaining rather broad. Carposporophyte with auxiliary cell remaining distinct at base, involucre slight, derived from elongation of ampullary filaments; ostiole usually present. Spermatangia forming a surface cortical layer.

Lectotype species: H. floresia (Clemente) C. Agardh 1817: xix.

Taxonomic notes: Tetrasporangia scattered in the outer cortex, cruciately divided.

Balakrishnan (1961b) has described in detail the structure and reproduction of H. floresia, based on material from Tuticorin, southern India. The genus is characterised by a usually thin but variously branched thallus, with a narrow cortex and lax medulla with many of the sparse filaments passing transversely across the thallus in young parts (denser and less transverse in old parts), auxiliary cell ampullae usually open and only a slight involucre around the carposporophyte.

Many species have been credited to Halymenia, with four species on southern Australian coasts. H. plana and H. muelleri are retained in Halymenia provisionally, although further studies may show that they represent a distinct genus. However, it is difficult to separate them on sectional thallus structure or degree of ampulla complexity, and all the southern Australian species have transverse medullary filaments in young parts at least, as well as refractive ganglionic cells (stellate only in H. kraftii).

References:

AGARDH, C.A. (1817). Synopsis Algarum Scandinaviae. (Berling: Lund.)

BALAKRISHNAN, M.S. (1961b). Studies on Indian Cryptonemiales - III. Halymenia C.A. Ag. J. Madras Univ., B, 31, 183–217.

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

Author: H.B.S. Womersley & J.A. Lewis

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.

KEY TO SPECIES OF HALYMENIA

1. Thallus foliose, simple or with broad lobes several cm across

2

2. Thallus thin, 200–400 (–600) µm thick, surface not mottled, medulla with mostly transverse filaments, with stellate but without refractive ganglionic cells; carpogonial branch ampullae with a few short secondary filaments of subspherical cells

H. kraftii

2. Thallus thin to relatively thick, surface mottled, medulla with transverse filaments when young but many irregularly orientated filaments in older parts, with abundant refractive ganglionic cells; carpogonial branch ampullae with several to numerous secondary filaments of elongate cells, converging above

3

3. Thallus usually with several broad lobes, occasionally entire and ovate, 250–400 (–600) [im thick, cortex 3–6 cells broad with the outer cortex mostly single layered

H. plana

3. Thallus with prominent marginal, unconstricted, lobes, mostly 800–1200 µm thick, cortex (5–) 6–10 (–12) cells broad with the outer cortex of anticlinal filaments of 2–6 elongate cells

H. muelleri


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