Florida is under invasion by a rapidly spreading foreign army that threatens to change the face, and even the climate, of the region. Many of the invaders were invited, to help improve the economy or beautify the state, then turned on their hosts.

More than 400 foreign plant species have taken root here, including the Australian melaleuca and Indian ficus that are spreading alarmingly, and the Brazilian pepper tree and African castor bean, poisonous to humans and animals.The danger to the Everglades is so serious that government biologists say Florida's famous river of grass may disappear within a lifetime.

"It is going to be very hard for any botanist in the future to tell what is native and what isn't," says Julia Morton, a University of Miami biologist who must drive two hours north along the high-speed Florida's Turnpike to see native flora. "Exotic plants are multiplying and becoming so widespread they are taking over."

Ironically, the most destructive species were introduced decades ago by well-meaning experts who did not understand the region's delicate ecosystem.

The melaleuca tree was planted in the Everglades 80 years ago in hopes of creating a lumber industry in what was seen as a useless wasteland.

Its economic potential proved elusive. Instead, the thirsty tree from arid regions of Australia soaks up the water, muscles out water-dependent species not used to competition, and the chemicals in its bark prevent all but the hardiest birds from even landing on it.

"Ten years ago in the east Everglades we found only 20 melaleuca trees," says botanist Robert Doren, vice president of the state's Exotic Pest Plant Council. "Now it has invaded 500,000 acres of the park, and 50,000 acres are essentially pure stands of melaleuca. Within our lifetime it could dominate the park - and a lifetime isn't very long."

The resultant damage has economic as well as environmental implications. Any major change in the Everglades will affect surrounding waters, drying up Miami's drinking water and sabotaging the shrimp, lobster and fishing industries in the Keys and Florida Bay.

One major factor contributing to the spread of the plant pests is Florida's rapid development. "Most of the plants that are a problem do best in disturbed areas. You take a naturally balanced area, then you build canals, roads, farms, and bring in a new plant with no natural predators," Doren says.

One ornamental plant that may haunt Florida's future is the ficus, a rapidly growing tree that can break up streets and sidewalks and take over whole yards.

Beside melaleuca and ficus, biologists generally agree Brazilian pepper and Australian pine present the major tree threats to Florida.