Marsilea villosa, the ʻihiʻihi (Hawaiian) or villous waterclover (English), is a species of fern that is endemic to the islands of Oʻahu, Molokaʻi and Niʻihau in Hawaii. It is found exclusively in areas that experience periodic flooding and become ephemeral pools within low elevation dry forests and shrublands. Standing water allows the sporocarp to open and release spores. It also enables the resulting sperm to swim toward and fertilize female ova. For new plants to become established, the waters must subside. Sporocarps only form once the soil has dried to a certain level. Like other species in its genus, the leaves of M. villosa resemble those of a four-leaf clover.
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- "Marsilea villosa". CPC National Collection Plant Profiles. Center for Plant Conservation. 2010-03-04. Archived from the original on 2010-10-28. Retrieved 2010-05-12.