The University of Hawai‘i (UNDATED) describes H. musciformis as, \"Clumps or masses of loosely intertwined, cylindrical branches, 10 - 20cm tall, 0.5 - 1.0cm 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. The authors state that H. musciformis can be easily distinguished from other native Hypnea spp. (In Hawai‘i) by, \"The presence of flattened, broad hooks at the tips of the branches.\"

The University of Hawai‘i (UNDATED) describes H. musciformis in more exact detail listing the following: \"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.\" Smith et al. (2002) states that, \"H. musciformis has ''apical hooks'' at the tips of its branches that attach or anchor the alga onto other macroalgae and any other available substrate. When this species is ripped from the substrate, these hooks are likely to be left behind to re-grow.\"

H. musciformis, when abundant, usually co-occurs with Ulva fasciata, a known weedy species in a genus known to require high nutrient flux for growth (Larned 1998). Therefore, the mechanisms that influence bloom formation in this species may be related to land use activities and nutrient input (Smith et al. 2002).

\"The genus Hypnea has a Polysiphonia type life history with isomorphic, dioecious gametophytes and tetrasporophytes and a diploid carposporophyte developing on the female gametophyte” (Masuda et al.1997 in Reis & Yoneshigue-Valentin, 2000).

Melo et al. (1997) discovered, \"A protein fraction, rich in agglutinins, obtained from H. musciformis by precipitation with ammonium sulfate that showed antifungal activity against the fungi Trichophyton rubrum and Colletotrichum lindemuthianum, with total inhibition of spore germination at concentrations of 500, 1000 and 2000 mu-g/mL.\"

Russell and Balazs (1994) report that, \"In Hawai‘i H. musciformis was originally planted on reefs in Kane‘oheohe Bay, Oahu, in January 1974, but has since spread to many other locations on Oahu and to other Hawai‘ian islands. H. musciformis, along with the previously introduced alien seaweed, Acanthophora spicifera, is now being prominently used as a food source by the green turtle (Chelonia mydas), an endangered species that frequents the Hawai‘ian Islands.\"

Salimabi (1980) found that, \"Pharmacological studies on K-carrageenan extracted from H. musciformis have shown that it antagonizes histamine-induced spasm in guineapig ielum and possesses anti-inflammatory activity against rat hind paw oedema induced by commercial carrageenan\".

\"H. musciformis is an important carrageenan resource of Brazil used in the industry of phycocolloid gelling agent\" (Bravin and Yoneshigue-Valentin, 2002).

SuriaLink (2003) reports that H. musciformis, \"Generally attaches subtidally to coral, stones or shells on sheltered tropical reef flats. It can also be cultivated on ropes suspended in the sea.\" The University of Hawai‘i (UNDATED) states that, \"H. musciformis is often found as an epiphyte on reef algae such as Sargassum echinocarpum, Sargassum polyphyllum, and Acanthophora spicifera.\"

A study conducted by Reis and Yoneshigue-Valentin (2000) suggests that, \"In H. musciformis, asexual reproduction predominates over sexual reproduction. There are more vegetative than reproductive thalli under environmentally stressful conditions for growth.\" Smith et al. (2002) reports that, \"H. musciformis is able to propagate vegetatively in all size classes examined, with the greatest success observed in the smallest fragments. The tips of the branches of this species are inflated and have characteristic ''hooks.'' These hooks twine tightly around axes of other plants. Once the epiphytic biomass of H. musciformis reaches a certain size or weight, wave action or other physical disturbance may crop the majority of the hypnea off the host plant, leaving the ''hooks'' behind. Our fragmentation study showed that these hooks can increase in weight up to 200% in a week, thereby rapidly propagating this species. In addition to the hooks, drift biomass that is ripped up can also disperse to new locations.\"

The University of Hawai‘i (UNDATED) states that, \"The success of H. musciformis in Hawai‘i is likely due to a rapid growth rate, ability to epiphytize other algae and easy fragmentation. Drifting fragments reattach to other algae, especially Sargassum, which can become detached during storms and float long distances, carrying the epiphytic H. musciformis with it. Dispersal may well have been enhanced via inter-island travel with fouled boat hulls.\" The authors also report that, \"H. musciformis is often found in large, nearly unialgal mats, and during the winter can represent 2/3 of the biomass of drift algae on windward and leeward beaches on Maui. These mats are tossed ashore in windrows up to 1.5 feet and are considered an odiferous pest. In peak blooms, thousands of pounds wash up on Maui beaches.\"

Since its introduction, H. musciformis has become a staple food source for the green sea turtle (see Chelonia mydas in IUCN Red List of Threatened Species). This worries biologists because the nutritional value of H. musciformis has not been determined for green sea turtles. Only further research will determine if a diet of H. musciformis is detrimental to sea turtle populations (University of Hawai‘I, UNDATED).

The University of Hawai‘i was awarded a $60,000 grant from the Hawai‘i Coral Reef Initiative. The grant will be used to fund research being carried out to control five separate invasive species in Hawai‘i including H. musciformis (Leone, 2001).

In Brazil H. musciformis is harvested as a source of K-carrageenan. The scope of what researchers and scientists must overcome is partially revealed in Faccini and Berchez's (2000) research. The authors found that H. musciformis has a recovery rate of 87% each month after harvest. This allows a crop every 35 days. For control mechanisms to be devised, scientists must overcome this extremely rapid growth rate. The growth rates obtained from the authors study reveal nearly 15% growth per day and are supported by cultivation experiments developed in the same region. In fact H. musciformis recovery is also much faster than in other economically important seaweeds growing in the same area, such as Pterocladiella capillacea, that take nearly 6 months per crop harvest (Faccini and Berchez, 2000).