Electronic Flora of South Australia Genus Fact Sheet

Genus MACROTHAMNION Wollaston 1968: 328.

Phylum Rhodophyta – Order Ceramiales – Family Ceramiaceae – Tribe Antithamnieae

Thallus 1 to 30 cm high, axes irregularly branched and corticated below with loose rhizoidal filaments; holdfast rhizoidal, epilithic or epiphytic. Axial cells each with 3 whorl-branchlets (2 in M. acanthophorum), simple or bearing a few simple pinnules, with or without minute spinous processes on upper cells; gland cells on special short branches. Cells uninucleate.

Reproduction: Gametophytes dioecious. Carpogonial branches borne on basal (= supporting) cells of whorl-branchlets, usually in a succession at branch apices, post-fertilization with rounded gonimolobes of carposporangia, partly surrounded by whorl-branchlets from below. Spermatangia terminal in clusters borne on the special gland-cell branches.

Tetrasporangia also borne on the special gland-cell branches, decussately divided.

Type species: M. pellucidum (Harvey) Wollaston 1968: 329, fig. 25.

Taxonomic notes: The genus contains 4 species, characterized by whorls of 3 (or 2) whorl-branchlets and both spermatangia and tetrasporangia borne on cells of the small special branches which bear the gland cells.

References:

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.

Author: E.M. Wollaston & H.B.S. Womersley

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 MACROTHAMNION

1. Whorl-branchlets in distichous pairs from each axial cell.	M. acanthophorum
1. Whorl-branchlets in whorls of 3 (rarely 2) from each axial cell	2
2. Thallus to 30 cm high; bearing whorls of 3 unbranched whorl-branchlets from each axial cell; gland cells (1–14) on short, often much-branched special branches	M. pellucidum
2. Thallus usually 1–8 (–12) cm high. Axial cells bearing whorls of 3 whorl-branchlets, some of which are always secundly branched with 1–5 simple branches; gland cells 1 (–3) on simple 2–4-celled short special branches	3
3. Thallus more or less robust, much branched, 1–4 (–12) cm high. Whorl-branchlets consistently in whorls of 3; gland cells on special short branches, sometimes extended to bear 2–3 gland cells	M. secundum
3. Thallus slender, sparsely branched, 3–8 cm high. Whorl-branchlets in whorls of 2 or 3; gland cells single on cells of short 2-celled branches	M. pectenellum

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