AT THE END OF A NARROW, RUBBLE-STREWN alley off Howard Road in Anacostia, the mean streets of Southeast give way to 20 acres of paradise. Doves and mallards take wing at a visitor's approach, and thousands of tropical plants -- some of them among the world's rarest -- flourish in meticulously tended greenhouses.

This is the U.S. Botanic Garden's Poplar Point Nursery, which serves as a growing area not only for plants used to landscape the Capitol and other federal buildings but also for rare specimens seized by the U.S. Customs Service.

"These are Renanthera imshootiana, an endangered species from Thailand," says Collections Supervisor Rob Pennington, displaying a potted orchid bearing a delicate reddish-orange flower. "It's a violation of CITES regulations to ship them here, so they were seized in Los Angeles." CITES is the acronym for the Convention on International Trade in Endangered Species. Nationwide 48 facilities are authorized to care for confiscated plants, but Poplar Point gets a major share because of the horticultural expertise of its employees.

"We have about 3,200 confiscated plants here now, including these orchids from Indonesia," Pennington says. There are more than 100 of them -- apparently thriving in small plastic pots. "They're nice and green now," he says, "but they were almost dead when we got them. It's a miracle that they came back at all."

Poplar Point is also home to hundreds of seized cacti and cycads -- primitive, palm-like plants that hail from the time of dinosaurs. Included among the cycads are three specimens of Encephalartos lehmanni.

"These are from South Africa and very rare," Pennington says. "They were seized at Los Angeles International Airport about three years ago, and we've been growing them ever since. Cycads are slow growers -- these are only three feet tall, but they're about 25 years old."

There are rarer specimens still.

"This Aristolochia macroura looks like a weed to most people," jokes Pennington, pointing to a scrawny, ivy-like vine. "It's really a choice specimen, though. It's extinct in the wild, so we're lucky to have one."

Then there's the Pittosporum boninensis, a drab-looking shrub -- but with two curious twists.

"There are only eight of these left in nature," says Pennington. "And what makes it even more interesting is that it's from Chichi Jima in the Bonin Islands, where George Bush's plane crashed in World War II."

Alas, Poplar Point itself is on the soon-to-be-extinct list. Metro's Ana-costia subway station, part of the Green Line, will be constructed on the site within the next year or two.

"We'll be moving everything to a new, state-of-the-art facility near D.C. Village this fall," Pennington laments. "It should be an improvement in many ways, but I'll still miss Poplar Point. It has a lot of charm."