Endangered Species in the Pacific Islands
Recovery Plan for the Marsilea villosa
There are 6 known populations of M. villosa with over 2,000 individual plants. This fern, found only in the Hawaiian Islands, was originally collected in 1918 by Louis Charles Adelbert Von Chamisso during a Russian exploring expedition.
Marsilea villosa, also known by its Hawaiian name ‘ihi ihi, resembles a four-leaf clover. It occurs either in scattered clumps or as a dense interwoven mat, depending on the competition with other species for limited habitat resources.
Marsilea villosa - Photo credit
Habitat & Distribution:
Marsilea villosa was originally discovered on the island of O‘ahu but was also known to exist on Moloka‘i and Ni‘ihau. A total of 11 populations have been reported of which only 3 currently occur on O‘ahu and 3 currently on Moloka`i.
The remaining M. villosa on O‘ahu are found in Koko Head, Lualualei, and Makapu‘u. Three populations
are known from western Moloka‘i.
Marsilea villosa is restricted to areas with irregular flooding. It is also restricted to low elevations in areas that were most likely dryland forest or shrubland in the past, but are now typically dominated by invasive alien vegetation.
This fern requires periodic flooding for spore release and fertilization, then a decrease in water levels for the young plants to establish. It typically occurs in shallow depressions in clay soil, or lithified sand dunes overlaid with alluvial clay. All reported populations occur at or below 500 feet (150 meters) elevation. While M. villosa can withstand minimal shading, it appears most vigorous growing in open areas.
The major threats to Marsilea villosa are destruction of natural hydrology; development; habitat degradation and resultant competition from invading alien plant species; off-road vehicles; fire; small population size and fragmentation; and trampling and other impacts from humans and introduced mammals.
This fern was federally listed as endangered on June 22, 1992. The population on Lualualei is on U.S. Navy land and they have undertaken some conservation measures to protect the endangered fern. Major conservation efforts have taken place at the Koko Head population of M. villosa.
The City and County of Honolulu and The Nature Conservancy of Hawaii maintain the area with the help of volunteers. Several botanical gardens are currently growing plants from the Koko Head population that are available for research, education, and reintroduction.