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Rhodophyta, Red Algae

Gelidium pusillum (Stackhouse) Le Jolis

Rhodophyta, Order: Gelidiales; Family: Gelidiaceae.


The generic name, Gelidium, means ‘gelatine’. The species name, crinale, means ‘hairy’.


The Gelidium has a long, cylindrical, sometimes slightly flattened thallus. Branching is irregular and lacking a specific shape. From a central axis, sub-branching occurs in two directions, pairs of short branches opposing one another upon each joint. Generally, the alga resembles a bush-like cluster of dense branches.


The thallus width is between 1 to several mm. Elsewhere in the world, it may grow up to 5 mm wide. Here, its length is usually 2-3 cm, but it can grow as long as 4 cm.


The alga is red, ranging from dark red to reddish-brown.

Special features

Especially large individuals clustered together resemble Pterocladiella capillacea, and the two can be easily confused. The distinction between the two genus is by the number of openings into the sporangium (cystocarp). The Gelidium’s cystocarp is two-directional (bilocular) and has spaces on both sides, whereas the Pterocladiella has only one opening. Sporangium is hard to identify in the field, and in its absence, it is difficult, therefore, to distinguish between the two. They can also, however, be distinguished based on the primary rhizoid: in the Gelidium, it emanates from the cells on the inside of the thallus, whereas in the Pterocladiella from those on the outside. This, too, is difficult to discern in the field. There is also a difference in the cross-section of the two: In the Pterocladiella, connecting cells are to be found in the cortex, and in the Gelidium in the medulla. Most researchers agree that the Gelidium crinale - a cross section of the thallus. two species are similar and difficult to differentiate (See also Dixson and Irvine, 1977; Kapraun, 1980).


Dense colonies of Gelidium appear in pools in the intertidal zone, usually near their edges and sometimes in deep water. Epiphytic individuals on other algae species have also been found.

Biology and reproduction

Not enough is known about the Gelidium’s life cycle, even though the genus is used as an important agar plant throughout the world. The Gelidium is the first plant from which agar was produced in commercial quantities in the seventeenth century.

Seasonality and distribution

The plant is perennial. Three-year old individuals have been found in the sea, but the life-span of a single thallus is usually one season.

Additional species

Literature describes several species of Gelidium in the region. These accounts are partial and doubtlessly attest more to the researchers’ knowledge than to the abundance of the species. Species described in Egypt and Lebanon most probably exist along the Israeli coast, too; however, there is a lack of professionals with the knowledge required to define those species. The most commonly described are:

Gelidium latifolium (Griville) Bornet and Thuret

= Gelidium corneum Hudson

Gelidium pectinatum (Schousboe) Montagne

Gelidium melanoideum (Schousboe) Bornet

Gelidium pulchellum (Turner) Kutzing

Gelidium spathulatum (Kutzing) Bornet.



The Gelidium is used to manufacture agar. Some species have healing powers, and in Japan they are used for burn treatment.

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