Somewhere in the Presidio — exactly where, the National Park Service isn’t saying — a life-and-death struggle is playing itself out.

It’s a tale of secrecy and of survival. It’s also a tale of sex. Just because the sex is between plants doesn’t make it dull.

The struggle is over nothing less than the fate of an entire species, in this case a rare plant called the Franciscan manzanita. That’s a plant so rare that it was long thought to be extinct in the wild. There’s only one surviving specimen of it in the wild, and it lives a lonely life in a corner of the Presidio, in a sort of botanical witness-protection program.

The Franciscan manzanita used to be common in San Francisco, before developers began digging it up to make way for temporal things like houses, apartments and stores. Unlike such big-ticket endangered species such as condors and elephants, the Franciscan manzanita is a humble, ground-covering bit of greenery. Thousands of people have driven near the last surviving wild specimen, in its secret location, without caring about it in the slightest.

Its defenders say that’s not the manzanita’s fault.

“That one plant is a symbol of the extraordinary biodiversity of San Francisco,” said Lew Stringer, associate director of natural resources for the Presidio Trust.

In 1947, when botanists thought the last Franciscan manzanitas were being bulldozed during development at the old Laurel Hill Cemetery area on Lone Mountain, they preserved clippings that ended up at the Tilden Park botanical garden in the Berkeley hills.

But it turned out that the Franciscan manzanitas from Laurel Hill weren’t the last ones in the wild after all. In 2009, a passing biologist with an eye for manzanitas found one growing in the Presidio near the Doyle Drive reconstruction project. The biologist, Daniel Gluesenkamp, said at the time that it was “like (finding) a unicorn.”

The next year, biologists spent $175,000 moving the plant to its new home, and then planted clippings from it at another secret site a half mile to the west.

The 2009 manzanita and its clippings cannot reproduce on their own. The clippings from the 1947 manzanitas cannot reproduce on their own, either.

But put the two of them together, as they say in the matchmaking business, and look out.

This winter, park service and Presidio Trust botanists got the idea to do just that. They brought 170 clippings of the Lone Mountain manzanitas from their foster homes at the Tilden Park botanical garden and two other gardens and transplanted them alongside the wild Franciscan manzanita. There was no formal announcement, in order to protect the secret site from rare-plant fanatics and their garden shears.

The rest will be up to the birds and bees, mostly bees.

When nature takes its course with human reproduction, the results are evident in nine months. With manzanita reproduction, Stringer said, it’s different. It could take years for the transplanted manzanita clippings to grow into proper plants and then pollinate with the surviving plant and its transplanted clones.

“The Franciscan manzanita was considered extinct in the wild for seven decades,” said Michael Chassé, biologist for the National Park Service. “The plant was saved and is now protected, but it cannot reproduce without ‘mates.’”

On Wednesday, Chassé returned to the secret spot with one last Tilden clipping, to replace one planted last month that had since died. He cradled the precious clipping — actually, a small twig with precisely seven leaves on it — as if it were plutonium.

After squirting the soles of his shoes with alcohol to kill any mold spores that could threaten the well-being of his clippings, Chassé hopped a fence, sidestepped some nonendangered poison oak and scampered down a path to a windswept hillside overlooking — well, said Chassé, better not say what it’s overlooking.

“Very few things are uniquely San Franciscan,” he said, digging a small hole for it. “There’s the Golden Gate Bridge. And there’s this plant.”

Chassé added, “It’s not often you get the chance to bring something back from the brink of extinction.”

The world of rare San Francisco manzanitas is a curious thing. The clippings from the 2009 Franciscan manzanita are located only 100 yards or so from the only remaining example of an entirely different manzanita — the Raven’s manzanita. A casual bystander would assume they were the same manzanita. But a manzanita wouldn’t.

The Franciscan manzanita has small pores, called stomates, on the bottom of its leaves that are visible through a magnifying glass. The Raven’s manzanita’s stomates are considerably smaller, visible only through a microscope.

However, it just might be possible for the Franciscan manzanita and the Raven’s manzanita to get together some day, too, if the two plants hybridize. Not every species can do it, but a manzanita can. And if a manzanita can survive real estate developers, biologists say, it must be a tough cookie.

“It’s a nuance you find in the world of manzanitas,” Stringer said. “The manzanita can make ‘mules.’ It might work.”

The Franciscan manzanita and the Raven’s manzanita may be rare, but manzanitas aren’t. There are 106 species of them worldwide, almost all of them found in California. The species includes small trees and flat ground-hugging shrubs that evolved 15 million years before the first human was buried at Laurel Hill, botanists say.

With any luck, the clippings will flourish, become pollinated and then produce tiny apple-like berries (“manzanita” means “little apple” in Spanish) with seeds inside — seeds that could become more manzanitas. If that happens in sufficient numbers, Chassé said he will gladly reveal to the general public where the manzanitas are. But that’s a long way off.

And it may take centuries to find out if the two manzanita species have managed to get together and form an entirely new, genetically distinct species. The manzanitas, however, have nothing else on their schedule.

And if all this doesn’t work and the Franciscan and Raven’s manzanitas go extinct, what then?

“For most people, it wouldn’t change the world,” Stringer said. “But it would be a loss, just the same.”