CLEMSON, S.C. — In the distance, beside a brick house in a tidy subdivision, the trees rose above a wooden fence, showing off all that had made the Bradford pear so alluring: They were towering and robust and, in the early spring, had white flowers that turned their limbs into perfect clouds of cotton.

But when David Coyle, a professor of forest health at Clemson University, pulled over in his pickup, he could see the monster those trees had spawned: a forbidding jungle that had consumed an open lot nearby, where the same white flowers were blooming uncontrollably in a thicket of tangled branches studded with thorns.

“When this tree gets growing somewhere, it does not take long to take over the whole thing,’’ said Coyle, an invasive species expert. “It just wipes everything out underneath it.’’

Beginning in the 1960s, as suburbs sprouted across the South, clearing land for labyrinths of cul-de-sacs and two-car garages, Bradford pears were the trees of choice. They were easily available, could thrive in almost any soil, and had an appealing shape with mahogany-red leaves that lingered deep into the fall and flowers that appeared early in the spring.

The trees’ popularity soared during a transformational time, as millions of Americans moved in pursuit of the comfort and order that suburban neighborhoods were designed to provide. “Few trees possess every desired attribute,’’ the gardening pages of The New York Times declared in 1964, “but the Bradford ornamental pear comes unusually close to the ideal.’’

Yet for all that promise, the trees wound up an unwieldy menace, one that has vexed botanists, homeowners, farmers, conservationists, utility companies, and government officials in a growing swath of the country across the East Coast and reaching into Texas and the Midwest.

In South Carolina, the fight has intensified. The state is in the process of barring the sale and trade of the trees, becoming the second to do so. Coyle, who tracks plants and insects that have intruded into South Carolina and tries to limit their damage, has organized “bounty’’ programs, in which people who bring in evidence of a slain tree get a native replacement in return.

The downsides of the Bradford pear were subtle at first. Its white flowers, as pretty as they were, emitted a fetid odor that smells almost fishy. But as the trees aged, more and more negatives emerged. They had a poor branch structure, leaving them prone to snapping and toppling in storms, sending limbs onto power lines, sidewalks, and the roofs of homes they were supposed to beautify.

But the most far-reaching consequence emerged as pear trees began colonizing open fields, farmland, river banks, and ditches, and rising between the pines along the highways from Georgia up through the Carolinas, edging out native species and upending ecosystems. The trees grow rapidly, climbing to as high as 15 feet within a decade. (They can ultimately reach 50 feet high and 30 feet wide.)

“You can’t miss it,’’ said Tim Rogers, general manager of a company that sells plants and supplies to landscaping companies. “It’s everywhere.’’

The Bradford pear is a cultivar of the callery pear, meaning it is a variety produced by selective breeding — in this case, devising a tree that did not have the thorns of some other varieties and was unbothered by pests.

But like the familiar plot of science-fiction stories, the creation that seemed too good to be true was, indeed, too good to be true. The Bradford pear had been billed as sterile, but that was not exactly right. Two Bradford pears cannot reproduce, scientists said, but they can cross-pollinate with other pear trees, and their seeds are spread widely by birds.

It is the resulting callery pear growth that alarms scientists: These trees spread rapidly, have thorns that are 3 to 4 inches long and cluster close together, disrupting life for insects and other plants.

“It’s a food desert for a bird,’’ Coyle said, noting that the trees do not sustain caterpillars and other herbivorous insects. “There’s nothing to eat there.’’

The callery pear, which is native to East Asia, was originally brought to the United States by federal researchers who sought a species that resisted blight and could be bred with the European pear to bolster fruit production. But scientists recognized its potential as an ornamental tree, spurring the development of the Bradford pear.

The tree’s popularity was largely concentrated in the Southeast and the mid-Atlantic coast. But it has been planted across the country, dotting lawns and the entrances to subdivisions and shopping malls.

“There are some places where I’ve seen entire campuses planted with this one tree,’’ said Nina Bassuk, a professor and director at the Urban Horticulture Institute at Cornell University. “If you’re there in April, it’s just this sea of white.’’ But then, she added, “Bradfords became a problem.’’ Aging trees were falling apart, she said, and “we started noticing them in places where they weren’t planted.’’

Officials in South Carolina added the Bradford pear to its State Plant Pest List this year and initiated a ban that goes into effect Oct. 1, 2024. Ohio is the only other state that has taken similar measures, with the callery pear, with a ban beginning in 2023. Delaware enacted more sweeping legislation this year that bars the selling, importing, or planting of any invasive species.

In other states, efforts to ban the trees have faced resistance from the plant industry, researchers said, given how much nurseries rely on their hardiness in using it as rootstock.