Story highlights The Franciscan manzanita is a flowering shrub found only on San Francisco peninsula

It has been believed extinct since 1947

A highway construction project removes trees covering the plant; passing biologist notices it

The plant and its 11-ton root ball are relocated; feds put shrub on endangered list

A flowering California shrub thought to be extinct in the wild for almost seven decades was added to the federal endangered species list Wednesday after a sharp-eyed biologist spotted the plant on a highway median while driving off the Golden Gate Bridge.

The last known Franciscan manzanita (Arctostaphylos franciscana) was discovered in 2009 during a highway construction project, and after genetic tests confirmed the species, the state spent $109,000 on a crane to move the plant and its 12.5-ton root ball to another site so the $1 billion project could continue, federal and state officials said.

The low-growing coastal shrub was relocated to another area in the Presidio of San Francisco, a 1,491-acre national park next to the Golden Gate Bridge, federal officials said.

The evergreen is estimated to be more than 50 years old and was growing a few feet from traffic along the Doyle Drive roadway, also designated as U.S. Highway 101, which connects the bridge and San Francisco, officials said.

The plant lay hidden under eucalyptus and other trees, officials said.

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When the trees were cleared, the manzanita became visible for the first time in decades and was spotted by biologist Daniel Gluesenkamp, director of habitat restoration for Audubon Canyon Ranch, who was driving home from speaking at a climate change conference, according to federal officials and the Wild Equity Institute.

Gluesenkamp noticed the unusual plant while driving 40 mph in heavy traffic, and he confirmed his suspicions about the plant's identity when he returned to the site a few days later, the institute said. The manzanita was last seen in the wild in 1947 when a botanist stood in front of earth-moving equipment and saved what was then believed to be the last known wild specimen from a construction site, the institute said. The botanist sent the plant to a botanical garden.

The manzanita found in 2009 had grown to a healthy size: Its roots stretched 20 feet wide and sank 18 inches into the soil, officials said.

The plant's bright green leaves are smooth, flat and wider toward the tips. The shrub likes open bedrock outcrops and reaches 3 feet in height, displaying pinkish flowers from January to April. It reproduces from seed after a fire or other disturbance, and the seeds are eaten and dispersed by raccoons, coyotes, foxes, deer, rodents, quail and turkey, the wildlife service said.

The agency is now proposing about 318 acres of federal and state parkland in San Francisco and the surrounding county be designated as critical habitat for the shrub, said U.S. Fish and Wildlife Service spokeswoman Sarah Swenty.

The plant is known only to exist on the San Francisco peninsula area and prefers serpentine soil, a low-nutrient area that allows it to out-compete non-native plants, officials said.

"Genetic diversity in plants is really important, as in animals as well," Swenty said. "When you lose a link in the chain, there are unknown consequences that you can't see.

"This plant has been used to prevent erosion on our hillsides in the San Francisco area, so it is certainly of benefit to people as well as plants," Swenty added.

The Wild Equity Institute said protecting the long-lost plant under the Endangered Species Act closes "one of our coldest conservation cases."

The institute petitioned the federal government to put the plant -- "a subtly charming flowering shrub," the group says -- on the endangered species list, the organization said. The Center for Biological Diversity and the California Native Plant Society co-petitioned for the protections, the institute said.