As wildflowers go, Torrey's mountain-mint isn't that striking. The short-stalked plant sports white blooms in late summer, but otherwise would be hard to pick out in a leafy lineup.
"You have to really be on a search to find it," says botanist Cris Fleming of Chevy Chase, who recalls spying some several years ago in a rocky outcrop on a Baltimore County farm.
Even when they're looking for it, though, scientists have a tough time finding Pycnanthemum torrei these days. It's rare - recorded in fewer than 20 places in the world - and likely to get rarer still, as homes, shopping centers, roads and parking lots gobble up more land in Baltimore's sprawling suburbs.
A report issued this month by conservation and smart-growth advocates warns that development in areas such as Baltimore and Washington threatens the survival of hundreds of rare animals and plants - including Torrey's mountain-mint - by destroying or disturbing their habitat.
"We live where the wild things are, and for the wild things, that spells trouble," says John Kostyack, a lawyer with the National Wildlife Federation and co-author of the report.
Nearly a third of the rarest species in the continental United States - about 1,200 plants and animals - live in the nation's 35 fastest-growing large metropolitan areas, according to the report.
At current rates of land consumption, the report projects that the 35 metro areas will build out a combined area the size of West Virginia - using up from 6 percent to 60 percent of their developable land. The report calls for the federal, state, and local governments to protect rare species by preserving their habitats and planning for more compact development.
Nine globally imperiled plants and animals are found around Baltimore. Among them are the sandplain gerardia, a relative of the snapdragon with little pink flowers. It grows in Maryland only on an unusual, prairie-like serpentine barren in Soldiers Delight Natural Area in Baltimore County.
Torrey's mountain-mint, which also favors rocky areas, has been seen in Baltimore, Howard and Frederick counties, though Fleming says the number of sightings has dwindled.
Another is the dwarf wedge mussel, a tiny freshwater shellfish that has been located in the sandy bottom of two creeks in Queen Anne's County and one in St. Mary's County. It is especially sensitive to pollution, including fertilizers, and to mud that might wash into the creek when nearby land is disturbed.
Most known Maryland populations of these and other highly imperiled species are on public lands, where they are generally protected from development. Government biologists set controlled fires at Soldiers Delight to help sandplain gerardia compete against other vegetation.
But conservation advocates point out that there are many more rare plants and animals in Maryland, and though somewhat less in danger of disappearing, many also are threatened by development. Twenty-eight animals and nine plants in Maryland are classified by the federal government as nationally endangered or threatened species, while the state watches out for 152 animals and 455 plants considered rare within the state's borders.
Endangered-species laws protect listed animals from being killed, and that oversight frequently extends to their habitat. While rare plants enjoy less legal protection on private land, laws regulating water pollution and wetlands disturbance help safeguard them.
In Maryland, state biologists review about 3,000 construction plans every year, and suggest changes to the projects in an effort to safeguard all rare species protected by federal or state law.
"We're a pretty regulated state, as far as land alteration," says Glenn Therres, associate director of wildlife and heritage for the Maryland Department of Natural Resources.
But on private land, owners have no obligation to protect rare plants, conservation advocates point out. Even if their habitat is on public lands, endangered species often are vulnerable to indirect effects of nearby development.
"It's not just development right on the site, but development all around," says Fleming.
Botanists and others have raised concerns about a pair of housing subdivisions being built too near to Araby Bog, a rare wetland in Charles County. (Those concerns initially led police to speculate about ecoterrorism in arsons there late last year, but investigators have discounted that theory.)
Sometimes the development threat comes from government. Plans to build a highway bypass around Hampstead in Carroll County were stymied for six years out of concern for the endangered bog turtle, until engineers redrew the proposed route to skirt its habitat.
Botanists also have warned that several rare plants grow along the projected path of the Intercounty Connector highway, which if built would ease commutes between Montgomery and Prince George's counties. DNR's Therres says state officials are working on how to minimize the project's impact.
Sometimes the effects of development are more subtle, with invasive plants or animals crowding out the native species.
"Some of the rare plants that grow at Soldiers Delight used to be found at Robert E. Lee Park," says Fleming, who once worked for the state. "Most of them are no longer there."
The culprit, she says, was European buckthorn, a shrub that apparently spread from yards of nearby homeowners, crowding out the rare plants.
Although relatively few people might notice the disappearance of something as rare and unremarkable as Torrey's mountain- mint, Fleming notes that a potent cancer drug and other medicines have been derived from other, previously unappreciated endangered plants.
"Every species is part of our whole web of life," she says. "They're there for a reason, because they got adapted to that habitat. We don't judge them by how attractive they are."
For more information on endangered species, go to www. baltimoresun.com/species.