North America, while not known as a plant diversity hot spot, in fact has nearly 4,600 wild relatives of crop plants grown in the United States, scientists say.

Those wild varieties include close relatives of globally important food crops such as sunflowers, beans, sweet potatoes and strawberries, they said.

The findings are good news for plant breeders who've relied increasingly in recent years on the wild kin of domesticated crops as new sources of disease resistance, drought tolerance and other traits, a release from the Crop Science Society of America said Monday.

Unfortunately, many of these "crop wild relatives" are threatened by habitat loss, pollution and climate change, said lead study author Colin Khoury of the International Center for Tropical Agriculture in Cali, Colombia.

An estimated 30 percent of U.S. plant species are now of "conservation concern," he said, and are possibly even more vulnerable because they've tended to be overlooked both by agricultural scientists and the conservation community.

"We always say that crop wild relatives are important and that they're threatened," he said. "I think what this study does is takes those general statements and puts some good evidence and documentation behind them."

"The window for securing these plants so that they're safe and can be used, it's narrowing for sure," Khoury said. "So it's really time to move forward and get these resources protected."