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Electronic Flora of South Australia Family Fact Sheet
Phylum Rhodophyta
Thallus usually erect, occasionally prostrate wholly or basally, much branched to foliose, branches terete to compressed or flat, branching radial to distichous, attached by loose rhizoids or a rhizoidal disc. Growth terminal. Structure uniaxial, the axial cells producing (centrally or distally) 2–20 periaxial or pericentral cells in whorls, or with single uniseriate determinate laterals, and in many taxa developing a filamentous or pseudoparenchymatous cortex on the axial cells. Trichoblasts present or absent. Pit-plugs with no cap layers. Rhodoplasts discoid, often in chains in larger cells, or ribbon like.
Reproduction: Gametophytes usually dioecious, occasionally monoecious; procarpic. Carpogonial branches normally 4-celled, borne on a supporting cell (in some taxa with sterile groups) which after fertilization usually cuts off an auxiliary cell (rarely with development directly from the supporting cell). Fusion between the fertilized carpogonium and auxiliary cell direct or via a connecting cell, the carposporophyte with or without a basal fusion cell, then producing branched gonimoblast filaments with all cells or terminal cells (or chains) forming carposporangia. Carposporophyte naked or surrounded by a pseudoparenchymatous pericarp one to a few cells thick, developed from pericentral or cortical cells adjacent to the procarp. Spermatangia produced singly or in clusters from cells of whorl branchlets, or as surface layers on male stichidia (on trichoblasts) or branchlets.
Tetrasporangia (rarely polysporangia or monosporangia) produced on whorl-branchlets or determinate laterals, or in stichidia or branchlets where they are cut off from pericentral or cortical cells, tetrahedrally or cruciately/decussately divided.
Life history triphasic with isomorphic gametophytes and tetrasporophytes.
Taxonomic notes: The Ceramiales is usually regarded as the most advanced order of the Rhodophyta, characterised by uniaxial structure, presence of pericentral or periaxial cells, and especially by the formation of the auxiliary cell directly from the supporting cell post-fertilization.
This Order includes over half the genera and species of Rhodophyta on southern Australian coasts.
References:
OLTMANNS, F. (1904). Morphologie und Biologie der algen, 1. (Jena.)
The Marine Benthic Flora of Southern Australia Part IIIC complete list of references.
Publication:
Womersley, H.B.S. (24 December, 1998)
The Marine Benthic Flora of Southern Australia
Rhodophyta. Part IIIC. Ceramiales – Ceramiaceae, Dasyaceae
©State Herbarium of South Australia, Government of South Australia
KEY TO FAMILIES OF CERAMIALES
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1. Branches uniseriate and without pericentral cells, periaxial cells usually present as a loose investment of the axes and only partially covering the axial cells unless they produce corticating filaments. Colourless trichoblasts usually absent. Carposporophyte naked with a gelatinous cover (in a few taxa with a few discrete surrounding filaments), but in some with loose protective vegetative filaments. Tetrasporangia lateral or terminal, naked or partially involucrate, borne on periaxial cells, filaments, or cortical cells | CERAMIACEAE |
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1. Branches uniseriate but with close, coherent, pericentral cells, with or without further cortication. Colourless (or pigmented) trichoblasts usually present, absent in Dasyaceae. Carposporophyte enclosed by a coherent, ostiolate pericarp formed of erect filaments from cells adjacent to the supporting cell. Tetrasporangia cut off from pericentral (or cortical) cells, enclosed within stichidia or branchlets | 2 |
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2. Axes sympodially developed, pericentral cells produced in a spiral clockwise manner (Dasya) or in alternating sequence (Heterosiphonia, Thuretia); trichoblasts absent but rhodoplastic pseudolaterals present; branching with walls of upper cells basally attached. Spermatangia on stichidia-like branches of the pseudolaterals. Tetrasporangia in stichidia on the pseudolaterals, cut off from whorls of pericentral cells | DASYACEAE |
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2. Axes monopodially developed, pericentral cells produced in an opposite or alternating manner; trichoblasts absent or present; branching with walls of upper cells basally free. Spermatangia on branches of the trichoblasts or in sori on the branchlets. Tetrasporangia in stichidia or branches, cut off from pericentral or cortical cells | 3 |
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3. Thallus usually compressed to flat, with 2 or 4 pericentral cells, the lateral ones cut off first and usually developing further. Tetrasporangia in sori on the thallus or in lesser branches, cut off prior to their cover cells | DELESSERIACEAE |
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3. Thallus terete to compressed or foliose, with | RHODOMELACEAE |
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