Pennycress: From Common Weed to a Valuable Biofuel Crop

Pennycress, a mustard-family weed that has colonized roadsides and grain fields across North America and Eurasia for centuries, is being rapidly transformed into a dedicated oilseed crop for biofuel production. Its seeds contain roughly 36% oil by weight, and that oil can be converted into renewable jet fuel and biodiesel with a carbon footprint substantially lower than petroleum-based alternatives.¹ What makes the story more interesting than a simple feedstock swap is how the plant’s biology aligns with a gap in American agriculture: pennycress grows during the winter months when Midwest fields would otherwise sit bare.

What Makes Pennycress Oil Useful for Fuel

The dominant fatty acid in pennycress seed oil is erucic acid, a very-long-chain monounsaturated fat that typically makes up about 31 to 37% of the total oil.² Linoleic and alpha-linolenic acids make up most of the remainder. This fatty acid profile is not ideal for food use (erucic acid is restricted in edible oils in many countries), but it turns out to be a reasonable starting point for hydroprocessing into renewable jet fuel and diesel. The long carbon chains in erucic acid are well suited to the cracking and isomerization steps that convert plant oils into drop-in hydrocarbon fuels.

One standout property of pennycress-derived biodiesel is its behavior in cold weather. Ethyl esters made from pennycress oil have a cloud point around −15°C, which is dramatically better than most other biodiesel feedstocks.³ Cold flow is one of the chronic headaches of biodiesel: soybean-based biodiesel, for instance, starts to gel at temperatures that pennycress blends handle without issue. Blending pennycress biodiesel with ultra-low-sulfur diesel showed highly linear correlations between blend ratio and key properties like viscosity, density, and energy content, with cold flow barely affected by the blend ratio. That predictability makes pennycress blends easier to integrate into existing fuel infrastructure.

Even modified “low erucic acid” pennycress varieties, developed to make the meal safer for animal feed, retain respectable cold-weather fuel performance. Biodiesel from these low-erucic lines has a cloud point around −6.8°C, which is still lower than canola or soybean biodiesel.⁴

How It Fits Into Existing Farmland

Pennycress is a winter annual. Seeds planted in the fall germinate before winter, survive under snow, resume growing in early spring, and are harvested by late May or early June. This life cycle maps neatly onto the fallow window in the corn-soybean rotation that dominates Midwest agriculture. The idea is not to replace corn or soybeans but to slip pennycress in between them, turning unproductive winter months into an additional harvest.

Field trials in Minnesota tested this concept in relay-crop and double-crop systems. Total oilseed production (pennycress plus soybeans together) consistently exceeded what soybeans alone would yield, though the soybean portion sometimes took a hit. At some sites, soybean yields dropped by 20 to 47% when winter oilseeds were included, while at one site soybeans were unaffected.⁵ The tradeoff depended heavily on local conditions, with water availability standing out as a key driver of pennycress productivity and downstream effects on soybeans.⁶

Separate trials confirmed that the optimal cropping strategy varied by environment. Pennycress yields tended to be greatest when the winter oilseed was harvested late rather than early, and the total oilseed yield of the combined system outperformed monoculture soybeans while providing ecosystem services on top.⁷ Not every approach works everywhere, though. When pennycress was interseeded directly into standing corn or soybeans (rather than planted after harvest), its own yields were low and it reduced relay-soybean yields by 13 to 32%, leading researchers to recommend against that particular method in the upper Midwest.⁸

Environmental Payoffs Beyond Fuel

The environmental case for pennycress goes well beyond carbon displacement. Bare winter fields in the Midwest are a major source of nitrogen runoff, which feeds the hypoxic “dead zone” in the Gulf of Mexico. Pennycress, growing actively during those months, pulls nitrogen out of the soil before spring rains can wash it away. In a four-year Illinois study, soil porewater nitrate-nitrogen at 45 cm depth dropped by 53% under pennycress compared to fallow plots.⁹ Even when pennycress itself received fertilizer, the reduction was still 34%. After termination, the top 30 cm of soil retained roughly a quarter less nitrate than fallow ground. Across four years of planting, the nutrient reduction held with no broad negative effect on overall soil characteristics.

Pennycress rotated with sweet corn in a separate set of trials reduced residual soil nitrate by about 42% more than fallow treatments, and life-cycle modeling of pennycress-inclusive cropping systems showed lower eutrophication potential and lower global warming potential compared to standard rotations.¹⁰

Weed suppression is another bonus. In relay-cropping trials, pennycress reduced weed biomass by 97 to 100%, far outperforming camelina’s 85 to 87% reduction.⁵ That level of suppression could reduce herbicide needs in the following growing season, though that downstream effect has not been well quantified yet.

A Spring Lifeline for Pollinators

Pennycress blooms in early spring, a period when very little else is flowering in agricultural landscapes. That timing makes it a potentially important food source for bees and other pollinating insects emerging from winter. Field observations recorded maximum insect visitation rates of about 67 insects per minute on pennycress flowers, comparable to canola and far higher than winter camelina.¹¹ Cumulative nectar production over the 2014 bloom period amounted to roughly 13 kg of sugar per hectare for pennycress. That is lower than canola or camelina in absolute nectar terms, but pennycress blooms earlier, filling a temporal gap when almost nothing else is available.

Multi-site surveys confirmed that pennycress is reliably attractive to beneficial insects across a wide geographic range, with average seasonal visitation rates of about 1.6 to 5.3 insects per minute depending on site and weather conditions.¹² The mix of insect visitors varied by location and temperature, but the overall pattern held: pennycress flowers draw pollinators during a time when they need food most.

Breeding the Weed Out of Pennycress

Wild pennycress has traits you do not want in a crop. Its seeds shatter easily (dropping to the ground before you can harvest them), its seed coat is thick and fibrous, it accumulates high levels of glucosinolates (bitter, potentially toxic compounds), and as noted, the oil is heavy in erucic acid. All of these are manageable in a weed but disqualifying in a commercial oilseed.

Researchers have tackled these problems using CRISPR gene editing, essentially performing a compressed version of the domestication process that turned wild grasses into wheat and corn over millennia. A recent study combined CRISPR-induced mutations that reduced seed glucosinolate content by 75% (by targeting transcription factors called MYB28 and MYC3), lowered erucic acid to levels comparable with canola, and reduced seed fiber content, all with minimal impact on seed yields.¹³ The result is what researchers call a “double-low” pennycress, echoing the terminology used for canola (which itself was bred from high-erucic rapeseed decades ago).

A parallel effort combined traditional mutant selection with gene editing to produce varieties marketed under the CoverCress brand, achieving low erucic acid and lower fiber through two independent pathways.¹⁴ These modified varieties represent different routes to the same destination: a pennycress seed that is useful not just for fuel but also yields a meal safe enough for animal feed.

What Happens to the Leftover Meal

After oil extraction, about two-thirds of the seed remains as a protein-rich meal. Wild-type pennycress meal contains around 31% crude protein, not far behind canola meal’s 36%. But it also carries much higher levels of erucic acid, glucosinolates, and crude fiber than canola meal, all of which limit how much can be mixed into animal feed.¹⁵ Feeding trials with broiler chickens found that wild-type pennycress meal could be included at up to about 8.5% of the diet before growth performance dropped off. Above 10%, feed intake and weight gain declined noticeably.

The gene-edited “golden pennycress” varieties, with their reduced fiber, erucic acid, and glucosinolates, could substantially raise that ceiling. Improved meal from these varieties has been characterized as a potentially valuable protein feedstuff for livestock, though the feeding trials to pin down exact inclusion limits in various species are still underway.¹⁶ Getting the meal right matters for economics: the value of co-products can make or break a biofuel crop’s profitability, as soybean growers already know from soybean meal’s outsized contribution to farm revenue.

Beyond animal feed, pennycress is also being explored as a plant-based protein source. The seed functions as a cover crop, oil feedstock for biofuel, and a novel protein source, and early extraction work suggests the protein has properties worth investigating for food or industrial applications.¹⁷

The Carbon Math

Life-cycle analysis gives pennycress-based renewable jet fuel a global warming potential of about 35 to 49 kg CO₂-equivalent per gigajoule of fuel, which is lower than jet fuel made from similar oilseeds and substantially lower than the petroleum jet fuel baseline.¹⁸ That range places pennycress-derived fuel comfortably within the thresholds required to qualify as an advanced biofuel and as biomass-based diesel under the U.S. Renewable Fuel Standard.¹⁹

A big reason the carbon numbers look good is that pennycress does not displace food crops on existing farmland. It grows during months when the land would be idle, so there is no indirect land-use change to account for. That is a chronic problem for biofuels made from corn or soybeans, where diverting grain to fuel can trigger additional land clearing elsewhere, eroding or even reversing the carbon benefit. Pennycress sidesteps this issue by design.

The hydroprocessing pathway converts pennycress oil into several products: renewable jet fuel (the main target), green diesel, naphtha, and liquefied petroleum gas. The meal can itself be used as boiler fuel for the processing facility, reducing external energy inputs.²⁰ This kind of internal energy recycling further improves the overall carbon arithmetic.

Economic Reality for Farmers

The environmental story is compelling, but farmers need to get paid. Early economic assessments have been sobering. In Minnesota relay-cropping trials, net income from adding pennycress to a soybean system was rarely different from monoculture soybeans.²¹ The extra oilseed production was often offset by reduced soybean yields and the cost of planting, managing, and harvesting the winter crop. The researchers concluded that improvements in net income are likely needed before the ecosystem benefits of oilseed cover crops are fully realized by growers.

More recent economic modeling paints a somewhat brighter picture, particularly when management is optimized. A study evaluating different corn maturity hybrids in a corn-pennycress-soybean rotation found annualized net benefits ranging from $315 to $945 per hectare. Choosing earlier-maturing corn hybrids, which free up the field sooner for pennycress planting, improved returns by up to 40% compared to full-season corn.²² Silage rotations produced greater net benefits than grain rotations at all sites, largely because earlier corn removal allowed more pennycress seed production. These results suggest that economic viability depends less on pennycress itself than on how cleverly the whole rotation is managed.

One missing piece in most economic analyses so far is valuation of ecosystem services. If carbon credits, water-quality payments, or cover-crop incentive programs assign a dollar value to nitrogen capture, erosion prevention, and pollinator support, the economics could shift substantially. Several states and federal programs already offer cover-crop payments, and pennycress qualifies for many of them.

The Soybean Cyst Nematode Problem

Any crop inserted into a soybean rotation has to be evaluated for its interaction with soybean cyst nematode, the most damaging biological pest in U.S. soybean production. Unfortunately, pennycress is an alternative host for SCN. Greenhouse studies confirmed that the nematode can reproduce on pennycress roots, though it is a less suitable host than soybean, with low reproduction factor values.²³ The concern is that maintaining even low-level nematode populations over winter, when the field would otherwise be inhospitable to SCN, could keep pest pressure higher going into the soybean growing season.

Breeding for SCN resistance in pennycress is underway. A standardized screening assay identified 15 pennycress lines rated as moderately resistant to one common nematode type, and eight lines moderately resistant to another.²⁴ No highly resistant lines have been found yet, but the moderately resistant germplasm identified so far could serve as the starting point for developing SCN-resistant cultivars. For sustainable adoption of pennycress in soybean rotations, solving this problem is not optional.

Scaling to a National Supply Chain

The aviation industry has committed to increasing sustainable aviation fuel production dramatically over the coming decades, but meeting those targets requires feedstocks that can scale without competing for food-crop land. Pennycress, along with camelina and carinata, is being evaluated as part of a diversified winter-oilseed strategy. Supply-chain optimization modeling has examined where processing facilities and biorefineries should be located to minimize logistics costs, taking into account regional crop production forecasts and infrastructure constraints.²⁵ The analysis highlights a critical bottleneck: even with favorable agronomy, scaling up requires grain handling capacity, oil extraction plants, and refinery infrastructure that does not yet exist at the volumes needed.

There is also a regulatory dimension to gene-edited pennycress varieties. Environmental risk assessments have flagged the possibility that fitness-related traits introduced through new genomic techniques could increase the spread and persistence of modified pennycress plants.²⁶ Pennycress is already a widespread weed, and varieties bred for higher yield or stress tolerance could potentially become harder to control if they escape cultivation. The irony of domesticating a weed is that making it a better crop might also make it a better weed. Managing that risk through stewardship protocols, seed containment, and careful trait selection will be part of the commercialization story as gene-edited varieties move toward wide deployment.

Seed Dormancy and Why It Matters for Planting

One quirk of pennycress biology that agronomists have had to work around is its seed dormancy behavior. Freshly harvested pennycress seeds can exhibit primary dormancy, meaning they will not germinate right away. This dormancy typically breaks within about a month of dry storage. But if fully after-ripened seeds are then soaked at low temperatures (around 6°C), they can enter a deep secondary dormancy that is much harder to break.²⁷ For farmers, this means planting timing and seed storage conditions matter. Seeds that sit through a cold, wet period before planting could end up locked in dormancy, leading to poor stand establishment. Understanding these germination triggers has been part of the groundwork needed to turn a plant that evolved to spread on its own schedule into one that germinates reliably when a farmer wants it to.