OVIEDO, Fla. (AP) _ A giant fern so rare in the United States that biologists had refused to reveal its whereabouts for fear it would be wiped out now faces extinction anyway because of a proposed development.

In the continental United States, the cuplet fern grows only in two small swampy spots a half-mile apart in the Black Hammock, a 7,680-acre wetlands area about 10 miles northeast of Orlando.

Identified in 1802, the fern used to grow on the southern edge of Lake Okeechobee but was plowed under for farmland decades ago. The fern, Dennstaedtia bipinnata, also is found in the Carribean and South America,

''It's a fern that's over your head. You can stand under it,'' said David Hardin, a research ecologist for the Florida Natural Areas Inventory. ''When you get out in a clump of these giant ferns you feel like you're out in the tropics.''

But a tiny piece of the Black Hammock attracted the interest of a retired priest, the Rev. John Caulfield of Lakeland, and he and another priest bought 40 acres and planned to sell it off in five-acre lots.

The St. Johns River Water Management District discovered Caulfield's plans 13 months ago when he had a road cut through the wetlands south of Lake Jesup without a drainage permit.

The road and the small development ''would bode most ill for the fern,'' said Peggy Lantz, who edits publications for the Florida Native Plant Society and the Florida Audubon Society.

Hank Whittier, a University of Central Florida biology professor who takes students on fern tours, says even cutting down trees nearby could let in light and cold wind that could change the fern's special climate.

Whittier has transplanted a few ferns to the university's arboretum, but they aren't as robust outside their native habitat.

The water district regulatory agency planned to fine Caulfield $1,000 and make him plant trees where the road was cut, but Caulfield has applied for an after-the-fact permit to build the quarter-mile road and develop eight lots. He already has sold two.

The water management district says Caulfield is trying to figure out a way to develop his property and protect the fern.

The water district also is considering several ways to protect the fern, said Pat Frost, the district's field office director in Orlando.

It will be difficult for Caulfield to convince the district that he can develop the property without damaging the wetlands, Frost said.

''We recognize the fern as a valuable resource and we would be remiss to not even address it,'' Frost said.

But the long-term outlook is not good. The entire Black Hammock is slowly being nibbled away by turf farms, vegetable farms, tree nurseries and rural homes, Whittier said.