Alpine pennycress is a charming little plant. Its low-growing rosette of green leaves is topped by leggy stalks bearing clusters of pinkish-white flowers. As they develop, these flowers transform into beautiful flattened seedpods that, in the words of botanist Liz Rylott from the United Kingdom’s University of York, “resemble a British old penny.” But alpine pennycress (Noccaea caerulescens) is notable for far more than its penny disguise. The plant is one of a select group—representing just 0.21 percent of the world’s known vascular plant species—that have evolved the ability to pull impressive amounts of valuable metals out of the soil. Known to scientists as hyperaccumulators, these plants undergird a developing industry that is looking to help secure the vital metals we want without wrecking the planet in the process.

Hyperaccumulators come in all shapes and sizes. Petite alpine pennycress accumulates zinc and cadmium, while shrubby, moth-pollinated Phyllanthus rufuschaneyi—a plant so obscure and narrowly distributed that it doesn’t have a common name—targets nickel. Pycnandra acuminata, a tree native to New Caledonia, has sap so nickel-rich that it “bleeds” a vibrant blue-green and is known as sève bleue, or blue sap, in French. Meanwhile, common buckler-mustard (Biscutella laevigata) collects thallium, and the cobalt wisemany (Haumaniastrum robertii), a plant in the mint family native to the Democratic Republic of the Congo, pulls up copper and cobalt.

In all, researchers have identified plants that hyperaccumulate arsenic, cadmium, cerium, copper, cobalt, lanthanum, manganese, neodymium, nickel, selenium, thallium, and zinc. Many of these are among the so-called critical minerals that are needed to build batteries and other components for electric vehicles, wind turbines, solar panels, and other facets of the green energy transition. They also include the metals that scientists warn could run short and derail global decarbonization efforts.

By pulling these elements out of metal-rich soils, hyperaccumulating plants can become as much as 5 percent metal by weight—a feat that would kill most species. And in the emerging field of phytomining, scientists and industrialists are learning to extract these valuable metals in a way that is much gentler on the landscape than conventional mining.

Right now, the race for critical minerals is sparking environmental destruction and human rights abuses. Cobalt mining, mostly in the Democratic Republic of Congo, has been compared to modern slavery. And concerns over access to critical minerals are stoking geopolitical tensions, including contributing to Russia’s invasion of Ukraine. As demand for these elements increases, high-grade and easily accessible deposits are getting tapped out, sending prospectors scouting for evermore extreme places to mine—like the very bottom of the ocean.

There is plenty of lower-grade ore available to be mined, as well as unprocessed mining waste and metal-polluted soils, but the traditional techniques to extract metals from these sources involve toxic chemicals and environmental destruction across wide areas. Yet harnessing the metals from lower-concentration sources, says Rylott, is exactly where phytomining shines. “Plants are really good at large, dilute problems,” says Rylott, who recently published a scientific paper reviewing how phytomining—originally an offshoot of bioremediation research—has advanced over the past several decades.

Getting the metal out of hyperaccumulating plants is simple in principle: burn the plants and separate the metal from the ash. Surprisingly, the quality of the resulting metal is often more concentrated and purer than that extracted by conventional mining. And the metal doesn’t need as much refining—it may even be in a form that manufacturers can use directly, minimizing the energy and effort required for processing. The leftover organic material can even be repurposed into fertilizer.

But putting that seemingly simple process into practice at industrial scale has proved difficult. Developing the infrastructure to extract metal from large amounts of plant biomass is “the greatest challenge for phytomining,” according to Antony van der Ent, a plant biologist at the University of Wageningen in the Netherlands, and coauthor, along with Rylott, of the phytomining review.

And there are other challenges. Many hyperaccumulators are small, slow-growing plants, says Om Parkash Dhankher, a plant biotechnologist at the University of Massachusetts Amherst. “Many of them are restricted to particular geoclimatic conditions” and are finicky to cultivate, he says. Or, worse, they grow too well, which is what happened when yellowtuft (Odontarrhena chalcidica, formerly known as Alyssum murale), a nickel hyperaccumulator native to the Mediterranean, escaped from an Oregon-based pilot project and turned into an invasive weed.

Even phytomining’s boosters say the technology is likely to remain relatively niche. Aside from the technological hurdles, there simply isn’t enough metal within the reach of plant roots to supply all the world’s needs. “Phytomining cannot replace conventional mining,” Dhankher says.

Despite these limitations, several phytomining startups have already begun commercial operations. Botanickel, for instance, is combining two different nickel phytomining projects—one with O. chalcidica in Greece, and another using P. rufuschaneyi in Malaysia—with the aim of producing partially plant-derived stainless steel. (Antony van der Ent serves as an advisor to the company.) GenoMines, a French firm, is using a genetically engineered plant in the daisy family and soil probiotics to farm nickel in South Africa.

To date, most phytomining work has focused on nickel, a high-value metal needed in large amounts to make batteries, stainless steel, and other materials.

Of the 721 known hyperaccumulating plant species, more than 500 take up nickel. For them, as with all complex evolved traits, it’s a matter of survival. Around the world, geological differences in the makeup of the earth mean that some soils—like those made of serpentine or ultramafic rocks—are naturally rich in nickel. For most plants, a heavy dose of nickel is deadly. But hyperaccumulators evolved the ability to absorb the metal into their tissues, turning otherwise toxic soil into an opportunity to thrive. Some scientists think hyperaccumulators’ high concentrations of bodily nickel even help protect them from pathogens and hungry insects.

In 2024, the U.S. Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E) announced seven grants totaling US $9.9 million over the next several years to develop nickel phytomining technology that could unlock a domestic supply of the metal from the more than 40,000 square kilometers (15,000 square miles) of serpentine soils that pepper the landscape in California and Oregon, and along the Pennsylvania-Maryland border.

One ARPA-E grant went to a team that includes Rupali Datta, a plant biologist at Michigan Technological University. She and her collaborators are investigating the role of soil chemistry and microbes in maximizing the phytomining potential of several known hyperaccumulators as well as vetiver grass (Chrysopogon zizanioides), a fast-growing species she’s previously used to clean up lead pollution. Meanwhile, Metalplant, a Delaware-based company, is collaborating with the Connecticut-based biotech firm Verinomics on a grant to genetically engineer *O. chalcidica. *Metalplant is already successfully using the species to mine nickel in Albania where it is native, but the company is hoping to tweak it to boost its nickel uptake and prevent it from becoming invasive when planted in North America.

Dhankher’s own phytomining efforts got a $1.3 million boost from the ARPA-E program. He aims to develop a genetically engineered version of Camelina sativa, a fast-growing member of the mustard family that is already widely grown in the United States for biofuel, so that it can become a better nickel accumulator. “The target is to create these plants that can accumulate 1 to 3 percent nickel,” Dhanker says. An advantage of C. sativa is that in some areas phytominers could grow three crops a year. If the plants accumulate at least 1 percent of their body mass as nickel, Dhanker says they could produce up to 25,000 kilograms of useful metal per square kilometer of soil each year (around 145,000 pounds per square mile). A typical electric vehicle battery contains about 30 to 50 kilograms (66 to 110 pounds) of nickel.

Nickel aside, phytomining also shows promise for collecting other minerals, especially cobalt, thallium, and selenium, Rylott and van der Ent wrote in their recent review. And the technique could even be used to target rare earth elements, a group of important metals that are common in the Earth’s crust but are mostly found at very low concentrations. For now, rare earth mining—an industry controlled almost entirely by China, with cascading effects on global trade relationships and supply chains—is expensive, energy intensive, and environmentally destructive. But if phytomining opens a new way to secure rare earth elements, says Lydia Bridges, a geochemist and senior sustainability consultant with Minviro, a company that helps mining operations measure and mitigate their environmental impact, “that would be pretty incredible.”

Though none have yet been commercially developed, scientists have identified a few natural hyperaccumulators of rare earth elements. Using plants to mine for rare earth elements would be “a huge step towards critical mineral security and, hopefully, sustainability,” Bridges says. But she adds a note of caution: “We do need to be a bit careful of environmental burden shifting.” While a welcome innovation, phytomining—of rare earth elements or anything else—is not an environmental panacea.

Growing hyperaccumulators at scale brings the same environmental woes as any other industrial crop, van der Ent points out: pesticide and fertilizer runoff, overdrawn water, and the loss of local biodiversity to a single-species operation. And while some outcrops of metal-rich soils host little life, others underpin fragile ecosystems, with, for example, metal-tolerant insects having evolved to live on hyperaccumulator plants.

But what phytomining could do is produce some metal while also remediating degraded land, sequestering carbon, and serving as the fuel for energy production or the raw material for biochar fertilizer, syngas, and other chemical creations. It could be one of many small but commercially viable enterprises that make for a more sustainable world. And along the way, it’s expanding our understanding of the endless and surprising feats that plants—even the pocket-sized alpine pennycress—are capable of.