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Chlorophyta, Green Algae

Ulva olivascens P. Dang

Chlorophyta, Order: Ulvales; Family: Ulvaceae.


The scientific name of the alga, Ulva, is the ancient name originally given to all algae. Since the days of Linnaeus, the name has been dedicated to the algae most dominant in nature. The Ulva olivascens is coloured green, shading towards olive-green, and hence its scientific name, olivascens.


The Ulva olivascens connects to the substrate through a holdfast from which several flattened thalli emanate. Often, holes can be found in the thallus. A microscopic overview reveals a smooth ‘leaf’ edge. The cells are usually scattered,

and only rarely can small sections of organized cells be seen. Usually a single Pyrenoid.


The size of the thallus varies according to environmental conditions, usually attaining a maximal length of 30 cm; however, lengths of up to 50 cm have been found. The width of the thallus at its bottom is about 110-115 microns.


The green colour of the Ulva olivascens is comparatively light, tending towards olive-green.

Special features

To identify the alga accurately, a microscope is required. In the field, several flattened thalli can be seen emanating from the same holdfast.


The Ulva olivascens grows in pools on the abrasion platform and sometimes in the subtidal zone. Sightings of the species at depths of up to 50 m. have been reported abroad.

Biology and reproduction

See entry in chapter on Ulva.

Seasonality and distribution

This species is apparently very common, perhaps the most  prevalent in the Eastern Mediterranean. It is widely distributed and is known throughout the Mediterranean and the North Sea.

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