The Franciscan manzanita - described by some as San Francisco's unicorn - thrives in a kind of botanical witness protection program.

Only one specimen of the low-growing shrub exists anywhere in the wild; until recently, it was believed to be extinct, having fallen victim generations ago in this city's battle between nature and development.

Today, the manzanita occupies a 7-square-foot patch of hillside in a 1,500-acre national park known as the Presidio of San Francisco. There is no sign attesting to its presence. It is not marked on any map. Coast live oak trees guard the weedy lot where California icons, serpentine rock and bright orange poppies, keep the modest bush company.

Park officials speak proudly of the manzanita, its ecological import, its improbable, now-you-see-it-now-you-don't story. Do not, however, ask them where it grows in their outpost at the foot of the Golden Gate Bridge. They will not tell you. Secrecy, and a nursery rich with seeds and rooted cuttings, are cornerstones of the Presidio's plan to reintroduce the rare plant.

But some here worry that federal park rules are not enough to protect a species that already disappeared on them once. The Wild Equity Institute is pushing the U.S. to list the Franciscan manzanita as an endangered species; in June the group sued to get the agency to act.

Because, as executive director Brent Plater likes to say, "it's hard to get more endangered than only one left in the wild."

The manzanita's scientific name is Arctostaphylos franciscana; aficionados of the plant, with its narrow, pointed leaves and bell-shaped flowers, call themselves arctophiles. In the first half of the 20th century, their ranks included some of the most famous botanists in California - women and men whose efforts to protect their passion were brazen, although ultimately unsuccessful.

Botanists believe manzanitas have been evolving for 15 million years. But by the 1920s, the habitat of the Arctostaphylos franciscana had shrunk to just three patches of rapidly developing San Francisco: Mount Davidson and two aging cemeteries.

Laurel Hill Cemetery, the final resting place of Gold Rush pioneers, was the last place the Franciscan manzanita grew in any abundance. In her 1939 classic "Flowering Shrubs of California," horticulturist Lester Rowntree rued the fact that the cemetery was "being regarded impatiently by the folk to whom any land is just so many building lots."

"If they can they will eradicate it as a cemetery and that will be the last of an old San Francisco record," she wrote, "and certainly the last of Arctostaphylos franciscana."

Rowntree was one of many botanists who dug up manzanita specimens and spirited them away. If the plant was doomed in the wild, these renegades figured, they could at least be kept alive in botanical gardens. One night Rowntree sneaked into the cemetery, ripped the plant out and drove it off to her home in Carmel. As she would tell a friend later, "I garnered it ghoulishly in a gunnysack."

Others, like Alice Eastwood, who was the first to describe the species, stood in front of bulldozers in a last-ditch effort to keep development at bay. Today, the old cemetery has been covered over with tony boutiques, pricey houses and tennis courts.

"It's a very special plant, only seen in San Francisco," said Peter Ehrlich, unofficial arctophile and official forester with the Presidio Trust. "That's what led to the emotional outbursts. Finding it. Losing it. It almost takes on mythical status."

The Franciscan manzanita became extinct in the wild in 1947.

At least that's what everyone thought.

But on Oct. 16, 2009, botanist Daniel Gluesenkamp was driving home to San Francisco from a climate change conference in Sonoma. Others at the event had waxed eloquent about complex engineering solutions and adaptation strategies. Gluesenkamp pushed for the most basic of fixes, he recalled, "things like saving the rare plants today. Find them where they are today and protect them."

Just after crossing the Golden Gate Bridge, he said, "something caught my eye. Just a flash of a glimpse. And it looked like a manzanita, in a site where they'd kind of removed some trees from behind it." The shrub was on a traffic island in the middle of a busy highway, part of a billion-dollar-plus construction project aided by federal stimulus funds.

Gluesenkamp, who is executive director of the Calflora database of Golden State plants, drove by three times, trying to get a better glimpse. He eventually called Lew Stringer, an ecologist at the Presidio Trust, who raced across the highway and officially identified the plant.

When he thinks back to his discovery, Gluesenkamp doesn't recall instant elation but, rather, a little bit of dread. The last thing he wanted, he said, was to have environmentalists blamed for derailing an important job-creating infrastructure project.

As it turns out, that didn't happen. Caltrans, which is in charge of the so-called Doyle Drive construction project, had ample money in the budget for environmental mitigation. On a rainy January night in 2010, the manzanita and its 21,000-pound root ball were dug up - a risky proposition with a nearly $200,000 price tag - and moved to the secret site where it grows today.

Shortly before the manzanita was moved, the Wild Equity Institute filed an emergency petition to get the plant protected under the Endangered Species Act. In a letter of response, federal officials said they did not see that "an emergency situation exists for the San Francisco manzanita."

Instead, the Fish and Wildlife Service said it would consider a possible listing under a normal timetable. Nearly two years have passed, and the agency has yet to make a final determination.

Which is why environmentalists have sued. Sarah Swenty, a spokeswoman with fish and wildlife's Sacramento office, said "people are working on it and doing the best they can to move it forward in a timely fashion." But workloads are heavy and resources scarce.

That is what worries Plater.

The longer the listing process drags on, "the probability of successfully saving these species is reduced," he said. "The race against extinction is a race against time."