An Inconvenient Plant

In a highly unusual move, Michael Chassé, the Presidio's rare-plants coordinator, has agreed to lead a reporter to the site of the very last genetic individual of the once-abundant Raven's manzanita — a location Presidio officials have long kept cloaked in secrecy.

A tall, wiry man with a ready smile, Chassé is outfitted in a brown fleece, thick green cotton pants, and heavy boots, giving him the appearance of a 40-year-old Boy Scout. He mounts a well-used bicycle and pedals expertly up a series of hills, dodging go-karts and choking on the greasy fumes of passing vehicles before veering off the beaten path. Chassé ditches his bike and ascends the side of the bluff, classifying every last bit of vegetation in sight: There's a bee plant! There's a sticky monkey flower — "and it's blooming!" And there's poison oak. In fact, there's a lot of poison oak.

The path to the manzanita soon begins to resemble a game of high-stakes hopscotch: Leap left at the gaping coyote burrow, right at the sun-bleached can of New Coke, and, when possible, avoid the walls of poison oak on all sides (the hopscotch game is fitting; the plant's namesake, Peter Raven, was a boy when he discovered it). Finally, Chassé vaults into a clearing blessedly free of the ubiquitous poison oak and grins — "Well, here we are." And yet there seems to be nothing to see. Apparently, when approaching the Raven's manzanita, you don't look up or even maintain eye level. You look down — way down.

The mythical endangered plant you'd hack through the jungle to behold in a Hollywood adventure film would be a 12-foot tiger-striped behemoth with orchid-like flowers as wide as dinner plates and tureen-sized pitchers capable of digesting large rodents.

Raven's manzanita, however, stands roughly shoulder-high to a Barbie doll. Past battles with a fungal pathogen have left it with several unsightly brown patches. Just inches off the ground, its dime-sized, round leaves ripple in the constant Pacific wind while its delicate, pearl-white flowers dangle like inverted wine glasses. Its gnarled red branches are no thicker than pick-up sticks. It's not what you would call ... majestic. When viewed from afar, it's rather unremarkable — except for the fact that it's the last of its kind.

Two hundred years ago, the manzanita and other low-lying native plants thrived in the Presidio's sandy dunes. Even in the late 19th century, large trees were as difficult to locate in San Francisco as parking spaces are today; it wasn't until 1883 that Major William Jones initiated the planting of the Presidio's 100,000 trees. It wasn't aesthetically motivated: The tall, heavily wooded stands of Monterey pine, Monterey cypress, and blue gum eucalyptus would, Jones declared, "make the contrast from the city seem as great as possible, and indirectly accentuate the idea of the power of the government." They also obscured the base's big guns.

For the sun-loving manzanita and its ilk, however, the trees were essentially a death sentence.

But now scientists and preservationists like Chassé hope to restore the Raven's manzanita and other native plants in the park to their previous glory. How? In large part, by axing thousands of tall, nonnative trees on 75 of the park's 1,480 acres.

And there's the rub. For the Presidio's most vocal neighbors and aficionados, beauty is only bark-deep. The park management's 30-year, $23 million plan calling for the removal of the trees in favor of dune restoration benefiting dozens of small, threatened plants has touched off a war on the former military base. In San Francisco, you can landmark a "historic tree" — but no one has ever thought to designate a historic bush. Maybe that's because city dwellers tend to be more emotionally attached to trees (some scientists, in fact, ponder whether humans' love of trees is hard-wired into our collective memories from the days we swung from them). In any event, local tree lovers opposed to thinning the Presidio's forests have gone so far as to accuse restorationists of carrying on the work of the Nazis.

Meanwhile, even ardent advocates of Raven's manzanita admit its long-term recovery is a long shot: No plant species has yet been revived from its last genetic individual.

So, if the last Raven's manzanita falls in the forest, would San Franciscans make a noise?

These days, a boy as obsessed with plants as Peter Raven was would probably have his phone tapped by the Drug Enforcement Administration. In 1951, however, the nation's priorities were different — the Red Menace overwhelmed the green one — and so the 14-year-old spent hours traipsing about the Presidio collecting samples.

In the years since, Raven's plant obsession has not waned. He has become, according to scientists contacted for this story, "the most revered man in the English-speaking world of botany" or, more concisely, "God." Securing a 20-minute phone interview with Raven, now the director of the Missouri Botanical Garden in St. Louis, required more than a dozen phone calls and e-mails to several assistants — and the minute the 71-year-old hung up the phone, he hopped a flight to Israel for a members-only botanical garden tour of the herbage of the Holy Land.

But with all of his accolades (and, it seems, deification), Raven knows you never forget your first species.

"It was a cool, sunny day like you often get in winter," he recalls. "I would head into the Presidio on weekends, looking for plants. I would come in at Baker Beach and collect on the bluffs. And I went up the hillside — and there was this plant. I knew it was a manzanita, but I didn't expect to see a manzanita there of any kind. People know the distribution of things pretty well, and manzanitas just weren't known there."

Yet it turned out the plant Raven had just stumbled across wouldn't be known anywhere else. The generations of ecologists and gardeners who have tended the manzanita "mother plant" — which is estimated to be more than 100 years old — since Raven's discovery have been won over by its sheer tenacity. While its forebears couldn't survive San Francisco's housing boom in the 20th century, the final bush is a plant that knows how to cheat death.

In 1958, oblivious Army landscapers undertaking a construction project halted their bulldozers only 20 yards from the manzanita. Thirty years later, a crew of Army lumberjacks felling large pines shading the mother plant nearly landed a tree on it. In rainy years, the plant develops a fungal infection called black smut that often kills 40 percent of its leaves and branches. And, in 1999 and 2000, it was swarmed by hordes of ravenous insects.

"It was like, 'Aaaaaah! The Raven's manzanita is being attacked!'" recalls Kirra Swenerton, the seed ecologist at the Presidio's native plant nursery.

When a horde of tussock moth caterpillars descended upon the plant not long ago, frenzied Presidio employees were relegated to picking off every last one by hand. "There's just the one [manzanita] left, and it's so vulnerable," Swenerton says. "And for that species to go extinct under our watch, in a national park — I mean, where else would you expect people to take better care of it? Oh, I was freaked out."

While the mother plant has escaped death, it has hardly lived a fruitful life. No Raven's manzanita seedlings have ever been discovered in the park.

Shortly after the Army nearly bulldozed the plant in 1958, numerous cuttings were taken. These were planted and cultivated into living insurance policies; roughly a dozen "clones" exist within about 100 yards of the mother plant, in addition to specimens at Tilden Park and UC Berkeley. As the name indicates, clones are genetically identical to the original — the sole genetic individual is the mother plant, leaving the species vulnerable to disease and changing conditions. Scientists can replicate Raven's manzanitas like so many photocopies, but without genetic variability a species cannot evolve. In the long run this, too, is a death sentence.

Botanists have long pegged the Raven's manzanita an "obligate outcrosser," requiring another genetic individual to pollinate it. With none in existence, decades of scientific reports gauged the species' hope of recovery as low.