To save an exceptionally rare wildflower, eight acres of brush will be burned, under tight controls, in the Sayville National Wildlife Refuge.

Otherwise, officials say, shade from spreading shrubs will doom the delicate sandplain gerardia — now the only federally listed endangered plant species in New York.

“The shrubs are encroaching on it pretty badly,” said Michelle Potter, manager of the Long Island National Wildlife Refuge Complex, which includes Sayville.

In March, the refuge burned 33 acres to protect the threatened plant. Last week’s rain delayed the planned eight-acre burn, which was rescheduled for a day between Nov. 7 and Nov. 20, depending on weather conditions.

Coastal grasslands were created by American Indians burning forests to grow crops or improve hunting, conservationists say. Europeans preserved them by grazing livestock.

Since then, countless acres of grasslands, from Maryland to Massachusetts, have been lost, largely to development.

Sandplain gerardia, a relative of the snapdragon known for its post-summer pink blossoms, favors the sandy loam found by the coast. The Sayville refuge is about two miles from the Great South Bay.

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Stuart Lowrie, a botanist for The Nature Conservancy on Long Island, said the “very small, unassuming” wildflower deserves the same protection as more showy species because the future of humanity could depend on biodiversity.

“We never know what we might need,” he said.

Andrew M. Greller, biology professor emeritus at Queens College, noted that unlike snapdragons most people are familiar with, which have curled petals, the sandplain gerardia’s are more flat and open, which makes it easier for pollinators. “This is a plant that attracts insects, so it’s colorful and it’s modified for insect pollination,” he said.

Potter said New York has one of the largest remaining stocks of sandplain gerardia, albeit at fewer than 1,000 plants; Long Island might be home to as much as half.

Periodically, controlled burns are scheduled in the Sayville refuge outside of wildlife hibernation and mating seasons, officials said. Fire breaks keep the flames from spreading, and firefighters from the U.S. Fish and Wildlife Service are deployed.

Nearly 3,000 nearby residents must be notified, along with businesses, schools, fire officials, Suffolk police and the Long Island Rail Road.

Certain conditions must be met the morning of the burn. For example, wind must be between 5 to 15 mph, and blow from the west, northwest or south, so the smoke can “lift and disperse,” Potter said.