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Electronic Flora of South Australia Genus Fact Sheet

Genus MYRIODESMA Decaisne 1841: 148

Phylum Phaeophyta – Order Fucales – Family Cystoseiraceae

Thallus 15–60 cm long, complanately branched, with a subdichotomous, terete to compressed, perennial stipe bearing (1–) 2–3 elongate, flat, simple or usually laterally branched, annual fronds, linear, entire or with spinous margins. Holdfast discoid-conical or divided; epilithic. Fronds 10–50 cm long, 2–20 mm broad, flat to strongly undulate, with or without a prominent midrib, wings relatively thin, margin with few to many spinous teeth, apices rounded. Vesicles absent. Growth from a single, three-sided, apical cell in an apical depression. Structure of a central medulla and a cortex of isodiametric cells with a surface meristoderm in the branched stipe, with a similar cortex but an inactive meristoderm and slight medulla in the annual fronds.

Reproduction: Conceptacles scattered over the wings of the annual fronds, bisexual, with a basal tuft of phaeophycean hairs. Oogonia with a single egg.

Type species: M. serrulatum (Lamouroux) Endlicher.

Taxonomic notes: An Australian genus of eight species (Nizamuddin & Womersley 1964), with 7 species on southern Australian coasts and M. peronii Nizamuddin & Womersley on the west coast of Western Australia.

Myriodesma is characterised by the subdichotomous, perennial stipe, each branch of which forms usually 2–3 flat, pinnate, fronds each season, with the basal 1–4 cm of the midrib remaining and thickening to later produce apically 2–3 more annual fronds. The fronds of most species are relatively thin and have a prominent midrib, at least in their lower parts.


DECAISNE, J. (1841). Plantes de l'Arabie heureuse. Archs Mus. natn. Hist. nat., Paris 2, 89–199.

WOMERSLEY, H.B.S. (1964). The morphology and taxonomy of Cystophora and related genera (Phaeophyta). Aust. J. Bot. 12, 53–110, Plates 1–16.

The Marine Benthic Flora of Southern Australia Part II complete list of references.

Author: H.B.S. Womersley

Publication: Womersley, H.B.S. (14 December, 1987)
The Marine Benthic Flora of Southern Australia
Part II
©Board of the Botanic Gardens and State Herbarium, Government of South Australia


1. Branches of annual fronds usually less than 1.5 mm broad, midrib absent or slight, with a single, irregular, row of conceptacles on each side 1

M. leptophyllum

1. Branches of annual fronds usually over 2 mm broad, midrib distinct, with two irregular rows or numerous scattered conceptacles


2. Branches of fronds usually 2–4 mm broad


2. Branches of fronds mostly over 4 mm broad


3. Branches of fronds strongly serrate throughout, with a single irregular line of conceptacles on each side of the midrib

M. serrulatum

3. Branches of fronds entire or irregularly serrate, conceptacles scattered over upper branches

M. integrifolium

4. Holdfast divided; annual fronds regularly bipinnate, flat, over 700 µm and 20 cells thick, with the terminal segments becoming fertile

M. harveyanum

4. Holdfast discoid-conical; annual fronds irregularly pinnate (or bipinnate), flat or convolute, less than 600 µm and 12 cells thick, with the terminal segments or whole laterals becoming fertile


5. Branches usually less than 1 cm broad, serrate; colour light brown, branches membranous, slightly convolute

M. tuberosum

5. Branches usually over 1 cm broad, entire or coarsely serrate; colour dark brown, somewhat cartilaginous


6. Branches (0.7–) 1–2.5 (–4) cm broad, usually coarsely serrate, especially above

M. quercifolium

6. Branches (0.6–) 1–2 cm broad, entire

M. calophyllum

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