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Electronic Flora of South Australia Genus Fact Sheet
Phylum Rhodophyta – Family Rhodomelaceae – Tribe Pterosiphonieae
Thallus erect, irregularly to pinnately branched with relatively long, linear, flat, indeterminate branches (1–) 2–6 (–7) mm broad, with short, marginal, determinate laterals 1–3 mm long and 1–3 mm apart; branches with a distinct midrib and conspicuous (usually) lateral veins (of the determinate laterals), the midrib denuded of the wings below. Trichoblasts occur on determinate laterals near branch apices or arise on the surface above the lateral veins. Holdfast fibrous. Structure. Apical cells segmenting transversely or obliquely usually 2–4 axial cells apart to form the determinate laterals, with the axial cells conspicuous throughout the thallus. Indeterminate branches have 6 pericentral cells, 2 larger lateral ones and 2 smaller ones on each surface, the lateral ones dividing laterally to give 3–6 cells between the veins but not dividing transversely; the terete determinate branches have pericentral cells of similar size. Blades with a single layer of larger cells and corticated by a single layer of small cells, thicker over the midribs. Cells generally uninucleate.
Reproduction: Reproductive organs occur on trichoblasts or branch clusters on the surface or the margins; propagules occur in D. harveyana.
Gametophytes dioecious. Procarps on surface or marginal trichoblasts. Cystocarps ovoid, pericarp corticated or not. Spermatangial organs on trichoblasts, with sterile basal cells and 1 to several sterile apical cells.
Stichidia in clusters on surface or margins of branches, terete, with mature tetrasporangia in short series, one per segment, spirally arranged, with 2 cover cells.
Type species: D. tridens (Mertens ex Turner)Greville 1830: li.
Taxonomic notes: A genus of about 7 species in southern Australia and South Africa. As well as the species and synonymy recognised below from southern Australia, D. myriacantha is now placed as a synonym of Pityophycus tasmanica.
The original spelling of Dictyomenia has often been given as Dictymenia in later lists.
References:
GREVILLE, R.K. (1830). Algae Britannicae. (Maclachlan & Stewart: Edinburgh.)
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 SPECIES OF DICTYOMENIA
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1. Main branches bi- to tripinnate; determinate laterals profuse and much branched on margins of main branches; reproductive organs on marginal determinate laterals | D. harveyana |
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1. Main branches irregularly and sparsely laterally branched; determinate laterals with few branches; reproductive organs in branch clusters on surface of indeterminate branches, situated over veins of determinate laterals | 2 |
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2. Main branches | D. sonderi |
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2. Main branches | 3 |
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3. Thallus moderately densely branched, lateral branches separated by few determinate laterals | D. tridens |
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3. Thallus sparsely branched, lateral branches separated by 2 to many determinate laterals | D. angusta |
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