For centuries, the wild grasslands and valleys of Minnesota were dotted with a type of cactus, spiky and round, that blooms every spring.

It grows about ankle high, roughly the size of a softball, and sprouts a violet or hot pink/fuchsia flower with a golden center. It survives almost exclusively on top of granite, growing on the large stones and outcroppings that jut out of the state's scattered prairies and wetlands.

Now, arborists warn, it needs saving — quickly. The threatened species has lost all but two of its largest populations in the state. Both of those surviving clusters of cactuses, unfortunately, are in active granite quarries, said David Remucal, curator of endangered plants for the University of Minnesota Landscape Arboretum.

"There's probably not more than a couple thousand left," Remucal said. "Those flowers. ... If you've ever seen a cactus flower, you know there's not a whole lot like it."

Remucal and the arboretum have an unorthodox plan to save the rare plant. Rather than try to protect the private land and granite quarries, they want to try to dig up, move and replant the cactuses inside a protected wildlife refuge.

Many of the replantings may fail, and up to 25% of those moved could die. But there may not be much of a choice if Minnesota is to keep a sustainable population alive, he said. The arboretum will collect enough seedlings to replace those that might die off during the transfer.

Many wouldn't think it, but Minnesota is home to three native cactus species. Two are types of prickly pear, which are relatively common.

The ball cactus, on the other hand, has always been rare and is mainly found in the mountains of Idaho and Montana. Sparse populations of it exist in the Dakotas as well. The fringe of its native range creeps into western Minnesota, where granite is more plentiful.

Granite seems to collect the right amount of silt and dirt in its crevices for the ball cactus to grow roots that are just deep enough to keep it stable during harsh winters and rough winds, Remucal said.

Few other plants can survive on the stone, giving the short cactuses plenty of sunlight.

They typically bloom around mid-June, and the flowers only last a couple weeks. Aside from the granite quarries, one of the only places in Minnesota with the cactus that's open to the public is Big Stone National Wildlife Refuge near Ortonville. The population in the refuge has dwindled over the years, with about 200 left, said Scott Simmons, refuge manager.

The site of them in bloom is always a draw that can bring visitors from around the state and region, he said.

"It's one of the rarest plants in Minnesota and it spits out those showy flowers for a very short amount of time," Simmons said. "Folks out here are very proud to have them in their backyard."

Remucal and the U's arboretum would like to transfer the 2,000 or so cactuses at the private quarries onto the granite outcroppings of Big Stone. It could bolster the refuge's population and keep up needed genetic diversity, Remucal said.

Several would also be brought back to the arboretum in the Twin Cities, where seeds would be collected and saved to replace any plants that die during the transfer or to be planted elsewhere.

"We'll be able to create a couple new populations," he said. "And we'll bring back some because it's all about having backups. The more cacti we can save, the more seed we can produce, so if they don't do well in one spot we can keep trying."

Ball cactus populations are doing relatively well in the Rocky Mountain States. But if the cactuses that have evolved and survived over generations in Minnesota are lost, there's no guarantee they could be replaced by those that live in the mountains, Remucal said.

"When you start moving plants, any plants, hundreds of miles away, you don't know if they'll be able to adapt to the Minnesota environment," he said.

A key legislative committee has recommended giving the arboretum $100,000 from the state's Environment and Natural Resources Trust Fund to complete the project. The funding still has to be approved by lawmakers.

State funding or not, the arboretum is committed to finding a way to save the species, Remucal said.

"It's nice to not just walk away from these endangered species," he said. "So people can see them and we can learn about these plants before they disappear."