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Electronic Flora of South Australia Family Fact Sheet
Phylum Rhodophyta – Family Rhodomelaceae
Thallus erect, radially branched, branches clothed with rhodoplastic trichoblasts (usually persistent) developed on successive segments, spirally arranged; pericentral cells 4–7, ecorticate or becoming heavily corticated, in some genera with adventitious monosiphonous filaments from the pericentral or cortical cells. Structure monopodial, with trichoblasts produced close to apices, simple or branched with non-adherent or rarely adherent walls just above the branchings; adventitious filaments simple or branched, arising from pericentral or cortical cells, similar to trichoblasts in dimensions; pericentral cells formed in alternating sequence, undivided or divided in a few species.
Reproduction: Gametophytes dioecious. Procarps borne at base of trichoblasts, on the last formed of 5 pericentral cells, which cuts off a single group or two groups of sterile cells and a 4-celled carpogonial branch. Carposporophytes with a basal fusion cell and branched gonimoblast with terminal carposporangia, usually replaced from lower cells. Cystocarps ovoid or urceolate, ostiolate, with cells of the erect filaments producing 2 outer cells, corticated or not. Spermatangial organs borne as a branch of trichoblasts, axial cells with 3 pericentral cells producing a layer of initials and outer layer of spermatangia.
Tetrasporangia occur in lesser branches bearing trichoblasts or in discrete stichidia borne on the trichoblasts or adventitious filaments, with 4–5 pericentral cells, one, or two opposite ones, becoming fertile; tetrasporangia single, either in a longitudinal line or spirally arranged, or paired and opposite, pairs decussate, with 2 pre-sporangial and in most genera also 1 post-sporangial cover cells.
Type genus: Lophothalia (Harvey) Kützing 1849: 797.
Taxonomic notes: Hommersand (1963, p. 346) listed 24 genera in the tribe, of which 11 occur on southern Australian coasts. However, Parsons (1975, p. 691) separated 6 genera in a separate tribe, the Brongniartelleae, based on their having trichoblasts branched in one plane, procarps with 2 sterile groups formed before and after the carpogonial branch, and the tetrasporangia with 2 or 3 pre-sporangial cover cells instead of 2 pre- and 1 post-sporangial cells.
Of these characters, the trichoblasts of some genera are branched largely in an upward curved plane, but this scarcely constitutes a tribal-based difference from those more irregularly branched in other genera. Similarly the difference in cover cells to the tetrasporangia (Brongniartelleae with 2–3 pre-sporangial and Lophothalieae with 2 pre- and 1 post-sporangial) appears to be slight, leaving the procarp sterile cell groups (1 in Lophothalieae and 2 in Brongniartelleae) as the most important feature.
It seems preferable to keep a single tribe for these genera which have persistent rhodoplastic trichoblasts. Alternatively, the genera could be separated on whether the tetrasporangia occur in normal branchlets (Brongniartella, Veleroa, Endosiphonia, Micropeuce, Holotrichia, Erythrostachys, Doxodasya, Lophothalia and Gonatogenia) or in specialised stichidia without trichoblasts (Haplodasya, Lophocladia).
References:
HOMMERSAND, M.H. (1963). The morphology and classification of some Ceramiaceae and Rhodomelaceae. Univ. Calif. Pubis. Bot. 35(2), 165–366.
KÜTZING, F.T. (1849). Species Algarum. (Leipzig.)
PARSONS, M.J. (1975). Morphology and taxonomy of the Dasyaceae and Lophothalieae (Rhodomelaceae) of the Rhodophyta. Aust. J. Bot. 23(4), 549–713.
SCHMITZ, F. & FALKENBERG, P. (1897). Rhodomelaceae. In Engler, A. & Prantl, K., Die natürlichen Pflanzenfamilien. T.1. Abt. 2, pp. 421–480. (Englemann: Leipzig.)
The Marine Benthic Flora of Southern Australia Part IIID complete list of references.
Publication:
Womersley, H.B.S. (24 February, 2003)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIID. Ceramiales – Delesseriaceae, Sarcomeniaceae, Rhodomelaceae
Reproduced with permission from The Marine Benthic Flora of Southern Australia Part IIID 2003, by H.B.S. Womersley. Australian Biological Resources Study, Canberra. Copyright Commonwealth of Australia.
KEY TO GENERA OF LOPHOTHALIEAE
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1. Thallus totally ecorticate | 2 |
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1. Thallus corticate, at least basally | 3 |
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2. Thallus with 7 pericentral cells, radially branched, trichoblasts irregularly and usually not complanately branched, often upwardly curved | BRONGNIARTELLA |
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2. Thallus with 4 pericentral cells, irregularly radially branched, trichoblasts radially arranged and more or less complanately branched, upwardly curved | VELEROA |
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3. Branches with one tetrasporangium per segment | 4 |
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3. Branches with two opposite, decussately arranged, tetrasporangia per segment | 9 |
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4. Tetrasporangia in a straight longitudinal line in the branch | HAPLODASYA |
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4. Tetrasporangia spirally arranged in the branch | 5 |
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5. Axial segments with 4 pericentral cells, stichidia and spermatangial organs with a monosiphonous pedicel | 6 |
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5. Axial segments with | 7 |
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6. Spermatangial organs and stichidia without trichoblast branches; cortication on lower axes only | LOPHOCLADIA |
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6. Spermatangial organs and stichidia with frequent trichoblast branches; cortication from close to apices | ENDOSIPHONIA |
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7. Axial segments with 5 pericentral cells | MICROPEUCE |
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7. Axial segments with 7 pericentral cells | 8 |
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8. Cortex of branches, and/or the lax, simple, trichoblasts and adventitious monosiphonous filaments, with occasional to frequent "gland" cells; pericentral cells soon inconspicuous | HOLOTRICHIA |
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8. "Gland cells" absent, monosiphonous filaments rigid, basally furcate, with isodiametric cells; pericentral cells conspicuous well below branch apices | ERYTHROSTACHYS |
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9. Four pericentral cells present; trichoblasts simple or branched | DOXODASYA |
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9. Five to 7 pericentral cells present; trichoblasts simple | 10 |
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10. Five or 7 pericentral cells present; trichoblasts (and monosiphonous filaments) unbranched, basal cells not markedly less in diameter than mid cells; reproductive organs on or in lesser branches | LOPHOTHALIA |
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10. Five to 7 pericentral cells present; trichoblasts with | GONATOGENIA |
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