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Rhodophyta, Red Algae

Peyssonnelia squamaria (Gmelin) Decaisne

Rhodophyta, Order: Gigartinales; Family: Peyssonneliaceae. In some other books, the Peyssonnelia squamaria is ascribed to other orders (additional information in the chapter describing the red alga order).


The generic name is dedicated to the French scientist J. A. Peyssonnel. The name of the species means squam,or ‘scale’ - aptly describing the scale-bearing appearance of this alga.


The Peyssonnelia squamaria is formed by flat, round and irregular scales. Several scales sometimes emerge from a common holdfast and cover one another. The algal surface shines and often sports parallel lines at a distance from one another, and rounded lines more densely packed. The

rounded lines delineate accelerated growth years, as in the rings in higher plants. The straight lines are light, multicellular rhizoids that develop on the algal underside. The rhizoids assist the alga in clinging to a substrate, and they also provide the ringed lines with a lighter colour.


The scales’ diameter changes, but is usually 2-3 cm in diameter. In some individuals, it may reach 5-7 cm.


The alga is bright crimson red. Some individuals may tend towards orange.

Special features

The Peyssonnelia squamaria can be identified by its dark colour and its circular thallus. Sometimes, the alga resembles a flaming red rose in form.





Peyssonnelia -cross section of the thallus’ lower section. Plates and multi-cellular rhizoids are evident. Peyssonnelia -general view of the thallus. Habitat

The alga grows in the subtidal zone and is never exposed during low tide. It can be found in niches and places where the light level is low. In particularly shaded habitats, such as marine caves, the alga may be found in shallower water, near the tidal level. Peyssonnelia squamaria have been found by Edelstein at eighty m depth upon a rocky substrate.

Biology and reproduction

The Peyssonnelia squamaria’s reproductive organs are concentrated in irregular swellings spread along the algal upper surface. It has an heteromorphic life cycle, in which the gametophytes and sporophytes are similar in shape.

Seasonality and distribution

The alga can be found throughout the year. It seems that at least some individuals are perennial. Distribution includes

the Mediterranean, the Atlantic Ocean (along its European, African and Canary Island coasts) and the coasts of the Indian Ocean and the Red Sea.

Additional species

Other species reported in various publications from the area include: Peyssonnelia bornetii Boudouresque and Denizot Peyssonnelia crispata Boudouresque and Denizot Peyssonnelia dubyi P. L. and H. M. Crouan Peyssonnelia harveyana P. L. and H. M. Crouan

Peyssonnelia inamoena Pilger Peyssonnelia orientalis (Weber van Bosse) Boudouresque and Denizot

Peyssonnelia polymorpha (Zanardini) Schmitz Peyssonnelia rosa-marina Boudouresque and Denizot Peyssonnelia rubra ( Greville) J. Agardh.

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