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Electronic Flora of South Australia Genus Fact Sheet
Phylum Rhodophyta – Order Ceramiales – Family Ceramiaceae – Tribe Heterothamnieae
Thallus erect, irregularly branched, with rhizoids from the basal axial cells attaching to and just penetrating the host, each axial cell with 4 similar whorl-branchlets over 200 µm long and successively branched 4–6 times; gland cells on outer cells of whorl-branchlets. Lateral branches arising on the basal cells of whorl-branchlets. Cells uninucleate.
Reproduction: Gametophytes dioecious. Procarps (2 or 3) borne on axial cells close to apices, with a supporting cell bearing a sterile cell and a 4-celled carpogonial branch. Carposporophyte with a terminal and several lateral lobes of carposporangia, not or slightly protected by lower whorl-branchlets; carposporophytes terminal, surrounded by 2–4 extended branches from the lower axial cell. Spermatangia on small, partly adaxial, clusters on whorl-branchlet cells.
Tetrasporangia sessile on basal to mid cells of whorl-branchlets, tetrahedrally divided.
Type species: T. lineatum Wollaston 1968: 361, fig. 33A–P.
Taxonomic notes: A genus of a single southern Australian species distinguished by the erect, tufted habit with lower cells of axes attached by just-penetrating rhizoids, axial cells with 4 whorl-branchlets which are successively branched 4–6 times, lateral branches arising on basal cells of whorl-branchlets and hence in a whorl of 4, gland cells subterminal on whorl-branchlets, and sessile tetrasporangia on mid to outer cells of whorl-branchlets, and especially by adaxial spermatangial clusters on whorl-branchlet cells. The latter feature separates it from species of Perithamnion.
Wollaston (1968, p. 360) considered Tetrathamnion to be intermediate between Heterothamnion and Perithamnion. Athanasiadis (1996, p. 189) considered the type species to be the same as Perithamnion (=Elisiella) arbuscula J. Agardh, but the latter is considered distinct from P. ceramioides and also T. lineatum. Illustrations of Athanasiadis (1996) of the type of P. arbuscula (Fig. 99) are distinct from his illustrations (Figs 100–102) of plants placed by Wollaston (1968, p. 361), and here, under T. lineatum, and study of large numbers of these two species supports their separation.
E. arbuscula has coarser whorl-branchlets and larger gland cells than T. lineatum and the latter has sessile tetrasporangia instead of those on branched adaxial filaments as in Elisiella.
Athanasiadis (1996, p. 190) also suggested that T. pyramidatum and T. ramosum are forms of T. lineatum, and this is accepted here.
References:
ATHANASIADIS, A. (1996). Morphology and classification of the Ceramioideae (Rhodophyta) based on phylogenetic principles. Opera Botanica No. 128, pp. 1–216.
WOLLASTON, E.M. (1968).Morphology and taxonomy of southern Australian genera of Crouanieae Schmitz (Ceramiaceae, Rhodophyta). Aust. J. Bot. 16, 217–417.
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
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