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Rhodophyta, Red Algae

Hypnea musciformis (Wulfen) Lamouroux

Rhodophyta, Order: Gigartinales; Family: Hypneaceae.


Both Hypnea and musciformis refer to the alga’s resemblance to moss.


The Hypnea musciformis is a fleshy, erect alga with central branches that display protrusions, which resemble side branches. Frequently, the upper edge of the thallus is hooked, but not always. A microscopic cross-section of the thallus reveals two rows of small outer cells that are rich in pigmentation, and inner cells that are bigger and brighter, some of them jointed. A single apical cell is to be found at the edge of each branch.


The thallus grows between 10 to 20 cm, but in certain individuals may reach 30 cm. The branches are 1 to 3 mm wide.


The Hypnea musciformis’s thallus is coloured green, ranging to light brown.

Special features

In the field, it is possible to confuse the Hypnea musciformis with the Acanthophora najadiformis: they cohabit the same habitat. One distinguishing feature is the hooks, but these are often missing. The side branches of the Hypnea musciformis are more regular, and those of the Acanthophora najadiformis are thinner, sharper and lighter.


The Hypnea musciformis is common along the rims of the abrasion platform that face the sea, between the intertidal zones. The horizontal range of its presence is wider than that of the Acanthophora najadiformis, but still limited.

Biology and reproduction

The Hypnea musciformis occupies a short horizontal range of the habitat. It is not found in deep water and does not rise to any great height. Most of the colony is to be found above the intertidal zone, in an area soaked by waves. Due to the short supply of carbon dioxide in the water, its photosynthetic rate is low, and it grows faster when exposed to air (triple the rate). Apparently, its low photosynthetic rate in the water is the major reason for its rarity in deep water.

The Hypnea musciformis is not a preferred foodstuff for fish, but Green Sea Turtles (Chelonia mydas) willingly add it to their diet.

The Hypnea musciformis has a three-stage life cycle. Reproductive spores are arranged along the side branches, and rounded sporangium (cystocarps) grow on or amidst the side branches or are attached to the central branch.

Seasonality and distribution

The genus includes about thirty species that are common in tropical and temperate seas. The Hypnea musciformis is one of the most common algae along Israeli coasts, and it can be found throughout the year.

Additional species

Besides the Hypnea cornuta, which is also quite common along the coast, there also appear to be other rare species of Hypnea, but these have not yet been defined. There are those who claim that the unhooked individuals of Hypnea are actually a different species. This claim seems to be unsubstantiated, since one may often find two incidences of the same plant. Hopefully, in light of the economic potential of the Hypnea, more research into this genus will be initiated in the region.

The two species described, Hypnea musciformis and Hypnea cornuta, are very common. Other species of Hypnea have been encountered that seem to be damaged individuals of Hypnea musciformis; however, these may be different species that have not yet been defined. Additional species of Hypnea reported in various papers written on the region are:

Hypnea cervicornis J. Agardh

Hypnea harveyi Kutzing Hypnea valentiae (Turner) Kutzing.

 Hypnea musciformis general view of the thallus, hook-like branch edges evident.

The Hypnea is an important agar plant that is cultivated as an agricultural product in various places around the world. In South America, marine farms specialize in net cultivation using a unique water spraying technique. Tests done in the Mediterranean and in India show that the alga contains materials that impede the growth of fungus. This further enhances the economic potential of the Hypnea musciformis as a food additive. In Turkey and Greece anti intestinal- worm remedies were once prepared from the Hypnea musciformis as well.

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