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Electronic Flora of South Australia Genus Fact Sheet
Phylum Rhodophyta – Order Ceramiales – Family Ceramiaceae – Tribe Heterothamnieae
Thallus erect, often basally clumped, attached by basal rhizoids to the host, occasionally with secondary prostrate axes, axial cells with 4 or 5 whorl-branchlets usually equal in size and over 150 µm long, successively branched di- (or tri-) chotomously with terminal chains of 2–3 small cells and prominent gland cells on outer cells. Lateral branches arising on subapical cells and becoming subdichotomous, also with shorter lateral branches arising from the basal cells of whorl-branchlets. Cells uninucleate or multinucleate.
Reproduction: Gametophytes dioecious or monoecious. Procarps borne in closely adjacent whorls of (1–) 2–3 close to apices of short lateral branches, with the carpogonial branches on normal whorl-branchlets. Post-fertilization the auxiliary cell fuses with the carpogonium via a connecting cell and divides, the upper central cell developing a terminal and lateral gonimolobes, not or partly protected by lower branchlets; carposporophytes lateral on continuing axes. Spermatangia terminal on further divisions of the terminal cells of the whorl-branchlets.
Tetrasporangia sessile, adaxial on the basal (or second) cells of whorl-branchlets, tetrahedrally or decussately divided.
Type species: P. ceramioides J. Agardh 1892: 30, pl. 1 figs 1, 2.
Taxonomic notes: Perithamnion is distinguished by subdichotomous branching from close to the apex, so that this branching occurs just above the whorl of whorl-branchlets, with shorter lateral branches arising from the basal cells of whorl-branchlets. The occurrence of spermatangia terminally on further divisions of terminal whorl-branch cells is also characteristic.
A genus of 2 species, the type and P. muelleri (Harvey) Womersley, on southern Australian coasts. Athanasiadis (1996, pp. 175, 189) considered that J. Agardh's second species of Perithamnion, P. arbuscula is generically distinct from P. ceramioides and identical with the type species of Tetrathamnion Wollaston. However, it is now separated (see above) in a separate genus, Elisiella, since the tetrasporangia are not sessile but are borne on branched, adaxial filaments of ovoid cells.
References:
AGARDH, J.G. (1892). Analecta Algologica. Acta Univ. lund. 28, 1–182, Plates 1–3.
ATHANASIADIS, A. (1996). Morphology and classification of the Ceramioideae (Rhodophyta) based on phylogenetic principles. Opera Botanica No. 128, pp. 1–216.
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 SPECIES OF PERITHAMNION
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1. Thallus | P. ceramioides |
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1. Thallus | P. muelleri |
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Email Contact: State Herbarium of South Australia |
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