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Chlorophyta, Green Algae

Flabellia petiolata (Turra) Nizamuddin = Udotea petiolata (Turra) Børgesen

Chlorophyta, Order: Caulerpales; Family: Codiaceae. In most books, the genus appears under its previous scientific name, Udotea.


Flabellia means ‘small fan’. Petiolata means ‘petiole’ or ‘stalk’, due to the narrow base of the alga, which resembles the stalk of a leaf.


The Flabellia is a flattened alga shaped like a leaf with a petiole and blade. The thallus is narrow at the base and suddenly widens, like a fan. When the thallus deteriorates slightly, several vertical axes can be seen, as well as three dark, concentric lateral axes. The alga contains a ‘root-stock’ that carries rhizoids towards the substrate and towards water. The thallus is unbranched and resembles a fan.


There is a large variance in thallus length, but it usually does not grow longer than 5 cm. The fan’s width is usually smaller than its length.


The Flabellia petiolata is dark-green; upon maturing and deterioration, the alga tends to change colour to olive-green.

Special features

The shape of the bladed ‘leaf’ with its vertical fibre during deterioration is unique, and enables identifying and defining the Flabellia petiolata with ease.



Flabellia petiolata (Turra) Nizamuddin = Udotea petiolata (Turra) B.rgesen


The Flabellia is usually found in potholes, often alongside a family member - the Halimeda tuna. The Flabellia sometimes migrates into deep sea, and individuals have been found at depths of 40 m.

Biology and reproduction

Studies into the depth to which the holdfast penetrates into a rocky substrate have found that the Flabellia penetrates up to 7 cm. This fact affords the alga stability and enables it to regenerate after being damaged or eaten. The same study, which was performed in the Bahamas and dealt with the holdfasts of various green algae, found that the Flabellia petiolata penetrated the deepest.

Seasonality and distribution

The global distribution of the Flabellia petiolata includes the Mediterranean and areas close by in the Atlantic Ocean.

Additional species

No additional species have been reported in the region, and the Flabellia petiolata is apparently the only species to develop in the Eastern Mediterranean. Another name that appears in literature -Udotea desfontainii Decaisne - is synonymous with Udotea petiolata, which is another name for Flabellia petiolata.



In some countries, the Flabellia has been given the popular name, ‘Mermaid Fan’.

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