So you want to add a native plant to your garden. A dark purple lupine would be the obvious choice, right? Wrong. How about a pink one?

Nope.

“Our native lupine is gone,” said Lois Stack, ornamental horticulture specialist for the University of Maine Cooperative Extension.

The native died out more than a decade ago, but the tall, spiky import from the Pacific Northwest became synonymous with Maine long before that. Because it is found in the wild, people assume it’s native, said Stack, a leader in the Cooperative Extension’s movement to help preserve the state’s landscape.

The movement has gained a following in the last 10 years, as Maine’s population has spread out. According to the 2000 Census, people who used to live in the city have moved to the suburbs, buying a few acres, often in formerly wooded subdivisions from which they’ve carved out yards and gardens.

“As people migrate into Maine and people accumulate more wealth, there are more constructed landscapes in Maine,” Stack said.

This isn’t necessarily a bad thing, she said, unless you’re dealing with invasive plants, which can overpower plants that occur naturally here. But just because something is exotic doesn’t mean it’s invasive.

“I would never advise people to not buy plants that are not native to Maine,” Stack said. “There are all kinds of wonderful plants that are out there, and 90 percent of the plants introduced have been great in the landscape. But some of these exotic plants, that means non-native, have become invasive problems in Maine.”

Eurasian milfoil, an aquatic plant, is perhaps the best-known of the invasives, making headlines for its potential to choke lakes and ponds. Another tall, spiky purple plant comes in a close second: the prolific purple loosestrife, which can produce 3 million seeds in a single season, and which can reproduce from the tiniest root fragment. The seeds are spread in the state’s waterways.

“Maine has been really fortunate in being up in the corner of the country and most of the watersheds are completely within the border of Maine,” Stack said.

But there are plenty of invasive plants that spread without the aid of water. Plants that are sold in nurseries because they are decorative. Plants that people see in the woods. Plants like Oriental bittersweet, which lures in wreath-makers and Martha followers each fall with its beautiful red berries in golden shells, or the ubiquitous burning bush, known for its deep crimson foliage in the fall.

These plants aren’t going to take over your yard, but birds eat their seeds and berries and scatter them all over. In the wild, they can overpower native species . And plants from the genus Ribes, including currants, gooseberries and alpine cherries, have long been banned in the state because they are an alternate host for a disease that affects white pine.

“I think we all love Maine for what it is and we all want Maine to keep its charm and its personality, and yet we are part of what is changing Maine,” Stack said. “One way that all of us, in our own back yards, can help keep Maine looking like Maine is to plant native Maine plants.”

That doesn’t mean cutting out exotic species. It means incorporating well-suited species into a cultivated landscape. It means choosing a native plant over an exotic with similar characteristics.

“One of the ways to decide on a new plant for a landscape is to opt for the native rather than the exotic,” Stack said. “A sugar maple will provide just as much shade as a Norway maple.”

Native isn’t always the way to go, though. Dale Pierson, a Biddeford nurseryman who specializes in wetland varieties, sells the fast-spreading speckled alder “all the time.” Many of the landscapers he deals with are re-creating habitat as required by law when developers fill and build on a wetland site, and the alders work well in this situation. But they’ll choke a field or a garden.

“Just because something is native doesn’t mean it’s not going to take over your yard,” Pierson said. “Native certainly is beneficial, but at the same time, there is a wide range of plants that are introduced that also are beneficial. They don’t misbehave.”

Among the indigenous plants that don’t misbehave, Pierson said, lowbush blueberry is a favorite. There are some, such as hobblebush, that succeed in the wild but don’t propagate in a greenhouse. And plants that normally are used to replace wetlands on developed parcels, such as the silky dogwood, are gaining favor as backyard plants, which presents its own problems.

“One of the problems we see is because the natives are becoming more in demand, there will be some available, but there will be a whole bunch of small ones, and some people want big ones,” Pierson said. “Instead of using it for this common wetland kind of thing, people want to plant one in their back yard, and they don’t’ want to wait for something [to mature] in their back yard.”

As the demand for native plants has increased, so has the number of nurseries providing them. The Cooperative Extension recently published a list of sources throughout Maine, which will probably grow as time goes on.

Often, the recommended native plants are superior to similar exotics, such as the sugar maple, with its glorious autumn foliage, or the creeping juniper, a Bar Harbor cultivar that has become the industry standard. In its native plants bulletin, now available online, the Cooperative Extension only recommends the best of the best, Stack said.

“They’re not just native, they’re not just in the woods, they’re good candidates for a developed landscape.”

The bulletin “Gardening to Conserve Maine’s Landscape: Plants to Use and Plants to Avoid” is available online at http://www.umext.maine.edu/publications/homegarden.htm.