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ORTONVILLE, Minn. - David Remucal and his small team of botanists and plant rescuers hopped from granite stone to granite stone under an overcast sky. They traveled single file through prairie grass to the top of a bedrock outcrop in Big Stone National Wildlife Refuge. There, they fanned out and searched the crevasses and cracks, the little indents in the granite, looking for signs of life of one of the few kinds of cactus to ever grow in Minnesota.

The plan to save one of the state's most imperiled species — the ball cactus — is a desperate one. There are only a couple of thousand left in the state, and many of those are in active granite quarries where they will eventually be dug up and killed. Nobody has tried planting or re-establishing wild populations in Minnesota before now.

Ball cactuses have always been relatively rare here, but they were once found throughout the Minnesota River Valley. They only grow in prairies, and even then only on the exposed bedrock and granite beds that jut out of the earth in those prairies. As the prairies have been lost to agriculture and granite outcrops lost to quarries, ball cactuses have almost disappeared from the state.

They grow in spheres to the size of golf balls and cluster together by the dozens. They develop tiny roots with the moss that lives on the stone, embedding in the thin layer of silt and dirt carried there by the wind. For a few days every June they bloom into a brilliant fuchsia flower that attracts scores of visitors, plant lovers and just about every type of pollinator around.

The plant's last stronghold is on the outcrops of a privately owned and active granite quarry a few hundred yards from the Big Stone refuge near here.

Remucal, curator of endangered plants for the Minnesota Landscape Arboretum, has been working with the quarry over the past few years to collect seeds from the cactuses before they are destroyed. The project is paid for with state lottery revenue. He eventually plans to uproot the cactuses, taking them one-by-one from the doomed outcrops of the quarry and replanting them inside the refuge, where they will be better protected. Until then, he is working with the seeds.

The team takes the seed from the quarry and propagates young cactuses at the arboretum where they grow to about blueberry size. Last November, they took about 100 young cactuses and planted them on an outcrop in the refuge.

On Thursday, the rescuers returned to the outcrop for the first time in months to see if any of those they planted survived the year.

"We're crossing our fingers," Remucal said in the days before making the 200-mile trip to the far western border of the state. "With a lot of these plantings in the wild the expectation is that they either don't succeed or they don't do great."

If one-in-four survived the year, he said, he would consider it a success and the new plants would have a decent chance to start reproducing on their own.

The problem is nobody really knows how to replant a wild ball cactus. Is it better, for instance, to plant them near the bottom of a slope where more rain will collect or will they get drowned out? Do they grow best in the thickest silt deposits, or will too many grasses and shrubs crowd them for sunlight? Do they need some shade and shelter from the wind in the crevasses?

The team planted the cactuses just before the weather turned bitterly cold in small groups up and down the slopes of the granite, in and out of the crevasses, in the hope that their survival and growth rates could help provide a blueprint for future plantings.

As Remucal walked up the outcropping Thursday there was reason to hope that the plantings worked, he said.

Conditions were perfect all winter and spring. Just after the blueberry-sized plants were put in the ground a deep snow came and covered them all winter, protecting them from the wind and providing plenty of water for their roots to grow in the spring melt.

But there was also cause to worry. The state has been stuck in a devastating drought since spring. It may have been too dry even for cactus to survive, he said.

Jon Titus, a retired professor and botanist who now volunteers with the U.S. Fish and Wildlife Service, was the first to spot a group of the cactuses: five of them planted in a circle near the bottom of a slope. They weren't just alive. They were plump, green and twice the size they were in November.

"Oh wow," Remucal said as he jumped over. "They're huge! That is so great. That is great."

Farther up the rock there were more plants; again, all were alive. At the top of the outcrop four more young cactuses were alive, their thin needles delicately wrapping around their spherical bodies. Those on top hadn't grown as much as those near the bottom, but they'll face less competition for sunlight and nutrients in the coming years. Inside a crevasse, two had died, but three more were still alive. The team counted and measured more than 20 areas where the cactuses had been planted. Of the 108 that were put in the ground, about 80 had survived their first year on the rock — far beyond Remucal's best hopes.

As volunteers continued counting and measuring the cactuses, Remucal jumped over to another granite outcrop and started scouting places to plant their next wave in the coming months as he was still coming to terms with what the success meant. Nearly four out of five were surviving. Thousands of more seeds have already been collected at the lab in the arboretum. Even if future years aren't as successful the group will be able to keep coming back, supplementing the populations with new plantings in the years to come.

"This is a great sign," he said.

If those year-old cactuses on the outcropping can hang on for another few years, with a little luck in the spring and more deep snow in the winter, they will likely start to reproduce on their own.

That will be the main measure of success, Remucal said. A population that sustains itself. If that happens, Big Stone Refuge could soon be the site of something not seen in Minnesota for more than 100 years — a growing cactus population.