Clumps or masses of loosely intertwined, cylindrical branches, 10 - 20 cm tall, 0.5 - 1.0 cm diameter, that become progressively more slender towards tips. Firm, cartilaginous, highly branched. Branching is variable and irregular, often tendril-like and twisted around axes of other algae. The ends of many axes and branches are flattened with broad hooks. Holdfasts are small, inconspicuous, or lacking. Usually red, but can be yellowish brown in high light environments or nutrient poor waters.

Usually red, but can be yellowish brown in high light environments or nutrient poor waters.

Easily distinguished from other native Hypnea spp. by the presence of flattened, broad hooks at the tips of the branches (see arrow on above figure). Often found as an epiphyte on reef algae such as Sargassum echinocarpum, Sargassum polyphyllum, and Acanthophora spicifera.

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Hypnea musciformis is a red alga with loosely intertwined cylindrical branches that form clumps or masses up to 20 centimeters tall, though plants are often broken by wave action before they reach full size. Branches are firm and highly irregularly branched, narrowing to broad, flattened, tendril-like hooks. These hooks make Hypnea musciformis easily distinguished from all other Hypnea species found in similar habitats. Holdfasts are small or lacking because the plants usually anchor themselves by attaching to other species such as sargassum (for example, Sargassum muticum). The tissue is usually a dark reddish-brown, though when growing in nutrient poor water color can pale to yellowish-brown. Hypnea musciformis is found abundantly in shallow coastal waters where it prefers calm, shaded subtidal reef flats, though it also grows in tidepools and rocky intertidal areas. In bloom stage, may be found free-floating. Hypnea musciformis is also a highly opportunistic invader.

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Mediterranean, Philippines, Indian Ocean, Caribbean to Uruguay

Hypnea musciformis is found worldwide in warm seas. It was introduced from Florida to Hawaii for aquaculture of carrageenan in 1974, has also been introduced elsewhere as an algal crop, where it has since taken over reef communities.

Medulla appear parenchymatous around central axial cell; cortical filaments with few divisions on radii, outer layer pigmented. Tetrasporangia zonately divided, in raised nemathecia, usually on ultimate branches; spermatangia borne in chains in slightly swollen nemathecia at base of branchlets. Cystocarps conspicuous, rounded, without discharge pore.

Pharmacological activity - antihelminthic (vermifuge);

Source of hydrocolloids - source of carrageenan;

Dawes, C.J. & Mathieson, A.C. (2008). The seaweeds of Florida. pp. [i]- viii, [1]-591, [592], pls I-LI. Gainesville, Florida: University Press of Florida.

Funk, G. (1955). Beiträge zur Kenntnis der Meeresalgen von Neapel: Zugleich mikrophotographischer Atlas. Pubblicazioni della Stazione Zoologica di Napoli 25(Suppl.): i-x , 1- 178, 36 figs.

Huisman, J.M., Abbott, I.A., Smith, C.M. (2007). Hawaiian reef plants. pp. [1]-264, numerous colour photographs. Honolulu: A publication of the University of Hawai'i Sea Grant College Program.

Masuda, M., Yamagishi, Y., Chiang, Y.-M., Lewmanomont, K. & Xia, B.M. (1997). Overview of Hypnea (Rhodophyta, Hypneaceae). In: Taxonomy of Economic Seaweeds. (Abbott, I.A. Eds) Vol.6, pp. 127-133. La Jolla, California: California Sea Grant College System.

Okamura, K. (1909). Icones of Japanese Algae. Vol. II pp. 21-40, Plates LVI-LX. Tokyo: published by the author.

Basionym: Fucus musciformis Wulfen

Type locality: Trieste, Italy (Silva, Basson & Moe 1996: 300).