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Electronic Flora of South Australia Family Fact Sheet
Phylum Rhodophyta – Class Florideophyceae – Order Nemaliales
Thallus (gametophyte) erect, 1–30 cm high, usually much branched irregularly to subdichotomously, branches terete, mucilaginous, multiaxial with a loose filamentous entwined medulla and a cortex of discrete, anticlinal, branched assimilatory filaments; calcified in Liagora; cells cylindrical to ovoid, rhodoplasts laminate to lobed or stellate, axile or parietal, with or without a pyrenoid; sporophyte (where known) minute, filamentous, branched. Growth of branches and filaments apical.
Reproduction: Carpogonial branches usually 3- or 4-celled, straight and terminating cortical filaments or lateral and usually curved on cortical filaments. Post-fertilization sterile involucral filaments usually produced from the supporting and adjacent cortical cells, often with descending rhizoidal filaments. Gonimoblast filaments branched, developing directly (or following division) from the fertilized carpogonium, with the cells of the carpogonial branch often fusing via broadened pit-connections. Carposporophytes usually compact, lying within the outer cortex, with or without an involucre, with terminal carposporangia. Spermatangia cut off from outer cortical cells.
Tetrasporangia cruciately divided, borne on minute filamentous sporophytes.
Taxa of the Liagoraceae are known in the field mainly from the conspicuous gametophytes, but the life cycle is now known, from the studies of Stosch (1965) on Liagora farinosa, Chen et al. (1978) on Nemalion helminthoides, and others, to involve minute acrochaetioid tetrasporophytes. The role of divided carposporangia ("carpotetrasporangia") known in several taxa has been clarified by Guiry (1990) for L. harveyana where the divided carposporangia are not formed by meiosis.
Life history triphasic (where known) and heteromorphic with macroscopic
gametophytes (monoecious or dioecious) and minute tetrasporophytes.
Taxonomic notes: Liagoraceae Kützing (1843, pp. 321, 328) pre-dates Helminthocladiaceae J. Agardh (1852, p. 410). The latter family name was proposed for conservation by Silva (1980, pp. 84,106) but the proposal was not agreed to by the General Committee (see Taxon Vol. 42, p. 438). Separation of Nemalion Duby and related genera with erect, straight, carpogonial branches (similar in position to a cortical filament) as the Nemaliaceae (Farlow) De Toni & Levi (Doty & Abbott 1964; Abbott 1976) is not supported (as Garbary et al. 1983, p. 81 found) since in several species (e.g. Helminthocladia densa) the lateral carpogonial branch may continue growth in the absence of fertilization and become comparable to a cortical filament.
References:
ABBOTT, I.A. (1976). Dotyophycus pacificum gen. et sp. nov., with a discussion of some families of Nemaliales (Rhodophyta). Phycologia 15, 125–132.
AGARDH, J.G. (1852). Species Genera et Ordines Algarum. Vol. 2, Part 2, pp. 337–720. (Gleerup: Lund.)
CHEN, L.C.M., EDELSTEIN, T., BIRD, C. & YABU, H. (1978). A culture and cytological study of the life history of Nemalion helminthoides (Rhodophyta, Nemaliales). Proc. N. S. Inst. Sci. 28, 191–199.
DOTY, M.S. & ABBOTT, I.A. (1964). Studies in the Helminthocladiaceae, RI. Liagoropsis. Pacific Sci. 18, 441–452.
GARBARY, D.J., HANSEN, G.I. & SCAGEL, R.F. (1983). The marine algae of British Columbia and northern Washington: Division Rhodophyta (red algae), Class Florideophyceae, Orders Acrochaetiales and Nemaliales. Syesis 15 (suppl.), 1–102.
GUIRY, M.D. (1990). The life history of Liagora harveyana (Nemaliales, Rhodophyta) from south-eastern Australia. Br. phycol. J. 25, 353–362.
KÜTZING, F.T. (1843). Phycologia generalis. (Leipzig.)
SILVA, P.C. (1980). Names of classes and families of living algae. Regnum vegetabile 103, 1–156.
STOSCH, H.A. VON (1965). The sporophyte of Liagora farinosa Lamour. Br. phycol. Bull. 2, 486–496.
The Marine Benthic Flora of Southern Australia Part IIIA complete list of references.
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 GENERA OF LIAGORACEAE
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1. Carpogonial branches | NEMALION |
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1. Carpogonial branches | 2 |
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2. Carpogonium slightly dumb-bell shaped; first division of zygote transverse; post-fertilization sterile filaments bridging the carpogonial branch, then producing above an involucre around the gonimoblast and below a tuft of rhizoidal filaments penetrating towards the medulla | HELMINTHORA |
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2. Carpogonium conical; first division of zygote transverse or oblique; post-fertilization sterile filaments not as above, developing irregularly and usually producing involucral filaments but not a distinct tuft of descending rhizoidal filaments | 3 |
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3. Thallus not calcified; first division of zygote usually oblique; terminal cells of cortical filaments usually enlarged | HELMINTHOCLADIA |
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3. Thallus calcified; first division of zygote transverse; terminal cells of cortical filaments not enlarged | LIAGORA |
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