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Electronic Flora of South Australia Genus Fact Sheet

Genus PLATYTHALIA Sonder 1845: 51

Phylum Phaeophyta – Order Fucales – Family Cystoseiraceae

Thallus usually 20–80 cm long, with several axes from a stoloniferous, branched, holdfast. Axes flat, complanately and alternately pinnately branched, straight to slightly flexuous, becoming denuded below. Laterals simple to basally or pinnately branched, compressed to flat, lying in the same plane as the axis or becoming basally twisted, basally constricted and tapering above, costate or ecostate, relatively thick, entire or with coarse marginal spines. Vesicles absent. Growth by an apical cell in an apical depression. Structure of a medulla of elongate cells with few or no hyphae and a cortex of isodiametric cells with a surface meristoderm.

Reproduction: Thalli dioecious. Receptacles developed from the whole or upper parts of the laterals, compressed to flat, with conceptacles either marginal or scattered; ostioles marginal or displaced slightly, or scattered over the surface; conceptacles unisexual, oogonia with a single egg.

Lectotype species: P. quercifolia (R. Brown ex Turner) Sonder.

Taxonomic notes: Platythalia includes the two southern Australian species, and probably also P. brandegeei (Setchell & Gardner) Womersley (1964, p. 104) from Gaudalupe I. The genus is characterised by its stoloniferous holdfast with several erect, complanately branched, axes, pinnate branching of the relatively thick and robust thallus, and the marginal or scattered conceptacles.

P. brandegeei was placed in a new genus Stolonophora by Nizamuddin (1969), being characterised by a stoloniferous holdfast, monopodial and compressed flexuous axes, and lateral branches of limited growth. All these features are found in the two Australian species of Platythalia, and there seems no reason to segregate P. brandegeei in a separate genus. The latter is closely similar to P. angustifolia, both having marginal to sub-marginal conceptacles and ostioles, whereas P. quercifolia has scattered conceptacles with ostioles on the flat surfaces of the receptacles. This latter difference, however, is scarcely of generic significance since the ostioles of P. angustifolia are often displaced towards the flat surfaces.


NIZAMUDDIN, M. (1969). Stolonophora, a new genus of Cystoseiraceae (Phaeophyta: Fucales) from Guadalupe Island, Mexico. Phycologia 8, 1–9.

SONDER, O.W. (1845). Nova Algarum genera et species, quas in itinere ad oras occidentales Novae Hollandiae, collegit L. Preiss. Bot. Ztg 3, 49–57.

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. Laterals 4–10 mm broad, with well developed coarse marginal spines 2–5 (–10) mm long

P. quercifolia

1. Laterals (1–) 2–3 (–4) mm broad, linear, without marginal spines

P. angustifolia

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