It will be illegal to sell nearly three dozen types of plants and trees in Maine if a new rule banning invasive terrestrial plants is adopted by the state.

The rule would ban certain types of plants that were imported to the state for ornamental or other purposes, but have since proved to spread quickly, choke out native species and disrupt entire ecosystems.

Proposed regulations have been developed for more than a decade and Maine would be among the last New England states to implement a banned plant list. The rule is not a solution to the state’s invasive plant problem, but it can make a difference, said Laura Zitske, a wildlife biologist with Maine Audubon.

“I don’t think anybody believes this is going to stop the spread of all invasive species. There is a lot out there,” she said.

“It is an important step in what is a tough battle and it certainly is a piece of the puzzle that is important to address.”

The proposed rule would make it illegal to buy, sell, import, export or grow 33 plants considered invasive, likely invasive or potentially invasive. Dealers that already have prohibited plants would be excused from the restriction until the end of 2017. Violating the rule could carry a fine of up to $500. The Department of Agriculture, Conservation and Forestry held a public hearing in December and is reviewing comments before finalizing the rule.

Many nurseries and landscapers stopped carrying listed plants years ago, but popular species are still carried by vendors across the state, said State Horticulturist Gary Fish.

During inspections this year, he found many examples of Norway maple, burning bush and Japanese barberry, three species listed on the invasive list, Fish said.

The horticulture industry in Maine started discussing the need to regulate invasives in 2006. Since then, Vermont, New Hampshire, Massachusetts and Connecticut have all implemented rules restricting invasive plants, according to Fish.

Rulemaking was prolonged in part because the stakeholder group reviewing the issue wanted to make completely sure plants added to the list were proven invasives in the state, Fish said. Maine made it illegal to bring invasive aquatic plants into the state in 1999.

“We wanted to make sure this was a true list that would not have an impact on nurseries in a difficult economic climate,” Fish said. The committee developing the rule reviewed 38 species and 33 met the criteria it established to prove a plant was invasive.

Some listed species, like multiflora rose, Japanese knotweed and Asiatic bittersweet, are well-known scourges battled fiercely by land trusts and conservation groups. Others, like Norway maple, an aggressive invasive that looks like native sugar maple, are not as familiar but equally damaging, said Jake Pierson, of Pierson Nurseries in Biddeford and president of the Maine Landscape and Nursery Association.

His business, like many others, stopped selling invasives years ago and the landscaping association supports a ban on some species.

“I think on the whole, the industry has done a very good job of educating people for why they shouldn’t buy them, but that didn’t necessarily stop them from buying them mail order,” Pierson said.

“Now we have scientific work and a legal piece to dissuade purchases,” he added.

The rule includes a five-year review and amendment of the banned plant list. People can petition the department to change the list on the basis of scientific evidence that a particular plant is or is not invasive.

While Pierson said that section of the rule is promising for nursery owners, Jeff O’Donal from O’Donal’s Nursery in Gorham doubts the department will consider exemptions for varieties of plants already on the list.

His company used to sell thousands of dollars’ worth of plants like autumn olive and honeysuckle, but has since stopped carrying the invasives even though customers still ask for them and can buy them from competitors, O’Donal said.

He now carries types of burning bush and Norway maple that can’t reproduce enough to be considered an invasive but thinks he’ll be stopped from selling them since the plants are on the banned list, O’Donal said. He doubts a committee set up to review his petition to the state will grant an exception for the plants.

“What I am afraid of is that they will choose the easy way out,” O’Donal said.

Despite his problem with the regulation, O’Donal thinks prohibiting some plants is a good idea.

“It is certainly time to do something,” he said. “We are surrounded by states with similar rules. This discussion has been going on too long.”