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Marsilea villosa

ListedJune 22, 1992
FamilyMarsileaceae (Pepperwort)
DescriptionSemiaquatic to aquatic fern similar to a four-leaf clover.
HabitatPonds and areas that will support its semiaquatic/aquatic habit.
ThreatsHabitat degradation and/or predation by wild, feral, or domestic animals.


'Ihi'Ihi (Marsilea villosa ), a semiaquatic to aquatic fern of the pepperwort family similar to a four-leaf clover, is 2-9.9 in (5-25.2 cm) in height. The plant has four leaflets at the tip of the stem, while the leaves are in pairs and bear a small, hard spore case on a short stalk at its base when fertile. All parts of this plant may be covered with a rust-colored pubescence.


M. villosa is an aquatic to semiaquatic fern that grows in small shallow depressions on level or gently sloping terrain. It requires periodic flooding to complete its life cycle. The spore cases normally are produced as the habitat begins to dry up and do not ripen unless the plant is drought stressed. When sufficient water is present, the plant reproduces vegetatively with young plants being produced on creeping rhizomes. The fern's habitat is dynamic, and may shrink or swell from year to year depending upon rainfall and other factors.


M. villosa was first collected in the Nuuanu Valley on Oahu and then later at Mokio and Moomomi on Molokai. The three remaining populations are at Koko Head and the Lualualei Naval Reservation on Oahu and near Laau on Molokai. The largest site is in the Lualualei Valley, where clumps of this plant are scattered among kiawe trees in an area of approximately 6 acres (2.4 hectares). The Koko Head population covers about 0.5 acres (0.2 hectares), but comprises the largest number of individual plants. The population on Molokai measures roughly 7 ft by 25 ft (2.1 m by 7.6 m).


The plant fauna of Oahu and Molokai, like all of the Hawaii Islands, has currently fallen vulnerable to habitat degradation and probable predation by wild, feral, and domestic goats, pigs, and cattle; competition for space, light, water, and nutrients by naturalized, exotic species; habitat loss due to fires; human recreational activities; and military exercises. The most immediate threats toM. villosa are competition from exotic vegetation, habitat degradation by off-road vehicles, and cattle. Off-road vehicles not only damage or destroy plants, but also disturb the soil, an action that promotes the invasion of competing exotic plant species.

Conservation and Recovery

The M. villosa population at Koko Head has been partially fenced through a management agreement between the city and county and the Nature Conservancy of Hawaii to prevent damage and habitat degradation by off-road vehicles.


U.S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N.E. 11th Ave.
Portland, Oregon 97232-4181
(503) 231-6121


U.S. Fish and Wildlife Service. 1996. "Marsilea villosa Recovery Plan." U.S. Fish and Wildlife Service, Portland, Oregon. 55 pp.

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