Limahuli Valley on Kauai's North Shore, with its green-mantled spires of volcanic rock, starred as Bali Hai in the movie "South Pacific." The Limahuli Garden, one of five units of the National Tropical Botanical Garden, occupies 17 acres of this improbably gorgeous place; an additional 985 acres preserve remnant upland forest.

"Limahuli" means "turning hands." The garden celebrates indigenous people's ties to the land, as well as the islands' endangered plant heritage. Its tour trail passes terraced taro (kalo) ponds, framed in lava rock at least 700 years ago and irrigated by canals diverting water from Limahuli Stream. The terraces - lo'i kalo - were part of an apupua'a, the traditional unit of land management: a pie slice with its apex in the mountains and its broad end in the sea. The system survived on Kauai into the mid-1900s.

Juliet Rice Wichman, member of a prominent Kauai family descended from New England missionaries, acquired the property in 1967 and donated the garden portion to the National Tropical Botanical Garden in 1976. Her grandson Charles "Chipper" Wichman Jr. is now the organization's director and CEO.

The group's mission, conserving Hawaii's native plants, includes searching the backlands for undiscovered or forgotten species, and propagating them in a state-of-the-art facility near Poipu on the South Shore.

That's the site of its other two Kauai gardens: the Allerton, a former private estate designed in the 1930s, and the McBryde, with native plants, "canoe plants" introduced by Polynesian voyagers - taro, ti , breadfruit, sugarcane - and palms, exotic culinary plants and ornamentals.

Unlike the McBryde, the Limahuli displays the natives in their ecological context. Short of a hike into the Alakai Swamp, Kauai's boggy heart, the Limahuli is the best introduction to a botanical lost world.

There's Pritchardia limahuliensis, a species of loulu - native fan palm - endemic to that single valley. Hawaii as a whole had 22 loulu species; several are now extinct. Their seeds, once dispersed by native birds, are now destroyed by introduced rats.

There's the koki'o ke'oke'o, a delicately scented white hibiscus (Hibiscus waimeae subspecies hannerae) once thought extinct. Botanical garden researchers rediscovered the plant, which can grow 30 feet tall, in a remote part of the Limahuli Preserve in 1976.

Limahuli's signature plant is the alula (Brighamia insignis), a lobelia relative that could have been a Dr. Seuss invention; it's been described as "a cabbage on top of a bowling pin." The alula's natural habitat is the precipitous Na Pali cliffs, where only a few individuals remain. No one has ever seen its pollinator in action; some speculate that it may be the elusive green sphinx moth, or something even more rare, if not extinct. Botanical garden botanists have rappelled down the vertical cliffs to hand-pollinate alula plants in situ. Alula has been successfully propagated by Martin Grantham at San Francisco State University, among others - but is hard to keep alive. An attempted introduction at Kilauea Point is looking unsuccessful. It really misses its cliffs, where it's being displaced by the likes of invasive sanseveria, the familiar houseplant "mother-in-law's tongue."

The islands' 900 or so endemic species are being crowded out by weedy invaders from all over the planet - an estimated 10,000 species. Some escaped from cultivation; others were deliberately planted to provide emergency watershed cover after the original forests were logged off. Even in the remote Alakai, ornamental ginger is muscling in on rare natives.

Limahuli's Invasive Forest Walk documents this hostile takeover: It has intentionally been left to the mercies of exotic autograph trees, yellow strawberry guavas and one of the worst offenders, schefflera. Another familiar houseplant, it's one of Kauai's worst invaders. Locals call it octopus tree because of its crimson tentacular flowers. Ever seen one in bloom? We hadn't, before Kauai.

We'd earlier met a couple of employees of the state agency that deals with invasive plants, on their lunch break in a Lihue city park. Theirs is a herculean job. They told us local nurseries are getting on board, but funding is meager and staffing is skeletal.

With their efforts, those of National Tropical Botanical Garden's explorers and propagators, and of nurseries and gardeners, there might still be a chance to preserve, even restore, one of the world's extraordinary hot spots of plant diversity.