East Lyme ― Native plants will be required in any landscaping submitted as part of a site plan starting Friday, though uncertainty remains about what that means.

An amendment to zoning regulations approved by the Zoning Commission last week specifies “native plants shall be used in all landscape plans.” No plants listed on the Connecticut Invasive Plant List will be allowed.

The regulation change was approved despite acknowledgment by some members that the language was too vague to be effective.

Resident Lindsay Rush stood up during the public hearing preceding deliberations to identify herself as a professor of science in support of using native plants in developments going forward.

But the way it’s written, she said using a single native plant “in a sea of non-natives” could satisfy the requirement.

A similar regulation in Newtown specifies at least 15% of shrubs and 25% of perennials can be non-native to the Northeast. Pollinator Pathway East Lyme founder and president Marjorie Meekhoff said that town’s regulations served as the basis for her suggested changes here in East Lyme.

Members also scrapped another part of the proposed amendment that would have updated outdoor lighting requirements to conform with the latest guidance from The Illuminating Engineering Society of North America. The recommendations stem from the international dark-sky movement to eliminate light pollution.

The commission voted 4-2 to approve the landscaping regulation without the lighting portion “in the interest of getting something done with this,” according to member Norm Peck III when he made the motion.

Newly-seated members Gary Pivo and Nancy Kalal, the dissenting votes, had asked for more time to come to a decision.

“I’d like to hear from a landscape architect on this, someone who’s an actual expert,” Pivo said. “While I’m very sympathetic to this, I’m just worried we’re being a bit oversimplified.”

Kalal said the commission hadn’t addressed Rush’s concerns that the language was too vague.

But member Michael Foley, appointed to a vacant seat prior to the election, shared Peck’s urgency.

“That’s a small enough change. I think that could be amended later,” he said.

e.regan@theday.com