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Rare fern likes floods, dry seasons
by Jan TenBruggencate
Hawait has its own native four-leaf clover, but it's not a clover. It's a fern.
The Marsilea villosa, whose Hawaiian name is 'ihi'iihi or 'ihi'ihilauakea, is a rare water clover-looking four-leaf fern with an odd life history.
The plant is on the federal endangered-species list, and the U.S. Fish and Wildlife Service recently completed a recovery plan.
The 'ihi'ihi was once found in at least 11 locations on Oahu, Molokai and Niihau. It's now down to five populations, one of them planted, on Oahu and Molokai. It might still exist in other locations, but because of the way it grows and reproduces, that can be hard to determine, the report says.
The little fern's densest population is in a flood plain in Koko Head, where it covers half an acre and forms a thick mat that mostly prevents other plants from moving in. The site is owned by the city and managed by The Nature Conservancy of Hawaii.
The plant has evolved to survive, and even thrive, in terrain that alternately floods and dries out. The ability to grow in both dry soil and water gives it an edge over most alien plants, which can't survive the flooding.
Like other ferns, 'ihi'ihi produces spores, but in this case the spores are contained in a hard structure that needs to be activated by immersion in water. Once in standing water, the structure opens and releases male and female spores, which allow the plant to reproduce sexually. It can also reproduce by sending out runners that grow into new plants.
Once the plant is growing, it cannot produce mature spore capsules until the soil dries out. The capsules can lie dormant in the dry soil for many years, awaiting the next flood.
In water, the fern's leaves are hairless and float at the ends of soft stems. In drier conditions, the leaves are hairy and grow on stiff stems. If it gets too dry, the leaves fall off and the 'ihi'ihi turns brown. With new rain, it bursts back into greenery.
Stands of 'ihi'ihi are killed off if their terrain is drained so that there's never standing water. They are damaged by off-road vehicles and animals, which tear up the fern mats and make room for alien plants. Fire during the dry season can kill them. They can't survive in dense shade, so the planting of trees around them reduces their viability.
For the plant to be considered safe, wildlife experts say it needs to be growing in healthy, reproducing populations in at least six sites on at least two islands, and those sites need to be protected from fire, alien plants and interference with their flooding-drying cycles.
The Honolulu Advertiser, January 6, 1997
Advertiser Kauai Bureau Chief Jan TenBruggencate writes weekly on environmental issues relating to Hawaii. He welcomes your ideas. Call him at (808) 245-3074, fax him at (808) 246-9107, or send email to tenb@aloha.net.
Links
| Pictures | Marselia villosa |
| Places | The Nature Conservancy's `Ihi`ihilauakea Preserve |
