Rumbling along the bumpy, dusty former sugar cane haul roads of Kauai's south shore, we pull up to a vantage point overlooking Lawai-kai (Lawai Bay) where crumbling red ochre-colored cliffs rise to dark green coffee fields. We advance slowly past giant agave, cacti, and euphorbia in the arid landscape when suddenly, a break in the overgrowth reveals a view of Lawai-kai, literally "waters by the sea."
This is where the tour group I am leading first encounters the dilemma facing the 1,100 or so remaining native Hawaiian plants. Unique in the botanical world, Hawaii's natives evolved in isolation with little or no defense against the thousands of aggressive exotic species introduced after Captain Cook's arrival in 1778.
"Ooohh," coos the group, as the tram stops beneath the shade of a ficus tree. Below, a stream winds beneath a small bridge, emptying into aquamarine waters where small waves break evenly on the beach fronting the Allerton Garden, one of five gardens that make up the National Tropical Botanical Garden (NTBG).
Allerton Garden was started in 1938 by Robert Allerton, a wealthy Chicago landscape designer and world traveler. Purchasing 67 acres of sugar land for $50,000, Allerton, with the help of his partner John Gregg, transformed a dusty valley into a verdant hideaway with tropical plants from around the world.
When I moved to Kauai five years ago from Japan, I never expected to work as an NTBG guide but, as they say, "you don't choose the garden, the garden chooses you." Now it is my job to summarize eons of history of the world's most remote island chain that is home to many of the world's rarest and most endangered plants.
It's a typical Hawaiian morning with cool trade winds blowing and sunlight dancing on the sea while a passing shower has left a rainbow arcing over the valley. Garden visitors from around the world admire the vista framed by flowering cacti that spill into Lawai Valley.
"None of these are native Hawaiian plants," I say, explaining that most plants associated with Hawaii – hibiscus, gingers, pineapple, and palms come from other parts of the tropical world.
"Not even those?" asks a man from Baltimore, indicating gracefully swaying coconut palms far below on the beach.
Hawaii does have native palms, called pritchardia or loulu palms, but the coconuts were brought by Polynesians, probably from the Marquesas Islands and Tahiti, starting around 1,600 years ago.
The group nods as they learn that all of the 27 recognized Polynesian-introduced plants were of the utmost importance either as food (taro, breadfruit, bananas), for medicine (mountain apple, noni, awa), for ceremonial purposes, or everyday uses such as dyes, nets, baskets, housing, clothing, candles, tools, and toys.
Descending into Lawai Valley, we pass the NTBG Conservation and Horticulture Center with its new nursery. It is here that many of the plants get their start and where much of the NTBG mission of conservation, research, and education is fulfilled.
Approaching the border of McBryde and Allerton Garden, we pause beside two wooden planters where I point to a small tree with charcoal-colored bark and oval curved leaves called Kanaloa kahoolawensis, one of the last two known specimens left on the planet. It's part of NTBG's mission to save such critically endangered plants.
With two-thirds of the world's vascular plants growing in the tropics, NTBG is one of hundreds of organizations that collaborate on a global scale to protect and preserve plants and their habitats for a healthier planet.
"And that?" asks a man, pointing to the second planter. It's the alula, found only on Kauai. Like many Hawaiian plants, its numbers have declined to dangerously low numbers. But through the efforts of NTBG and others, the plant has been successfully propagated and has actually experienced a modest comeback.
"Hawaii has more endangered plants than anywhere else on earth," says NTBG Director Chipper Wichman, "making us a hot spot for conservation and a truly invaluable national resource to preserve the nation's tropical flora."
Our tour proceeds through the Allerton Garden, the most ornamental and formal of the NTBG garden sites. A network of dirt pathways and lava rock stairs lead us through a mosaic of living "rooms" composed of junglelike foliage: oversized heliconia, giant anthurium, and dazzling epiphytic orchids that cling stubbornly to shady monkeypod trees.
Trails weave through towering gingers, past rushing waterways and neatly groomed tropical corridors of green hues, exotic textures, and forms. Java finches twitter in gracefully arching gnarled kiawe (mesquite) trees while green-striped bamboo creaks eerily in the breeze.
The group has now reached the expansive green lawn beside the Allertons' former beachside estate, the palms we'd looked down on earlier now soaring above. Nearby, members of the NTBG Conservation Department transplant rare endemic plants as part of a coastal restoration project.
We pause here, watching as the battle for the survival of Hawaii's native flora is quietly waged, one plant at a time.
• To learn more about the National Tropical Botanical Garden visit www.ntbg.org