Understanding the Pennycress Plant
Pennycress, scientifically known as Thlaspi arvense, is a winter or summer annual plant belonging to the mustard family (Brassicaceae). Originating from Eurasia, it has become a common and widespread weed in disturbed soils throughout temperate regions globally. The plant's distinctive, coin-like seedpods and pungent odor when crushed make it relatively easy to identify. Historically, it was mainly known for its weedy nature and occasional use as a wild edible. However, thanks to targeted agricultural research and selective breeding, its potential is being re-evaluated for numerous modern applications, primarily as a cash cover crop.
Identifying Pennycress
To correctly identify pennycress, look for these key features:
- Growth Habit: A hairless, erect annual herb growing between 1 to 2 feet tall.
- Leaves: Basal leaves are spatula-shaped and form a rosette that often withers as the plant matures. Stem leaves are alternate, narrow, and clasp the stem with ear-like lobes.
- Flowers: Tiny white flowers with four petals, characteristic of the mustard family, form dense clusters at the tips of stems.
- Seedpods: The most recognizable feature is the large, flat, round seedpod (silicle) with a prominent notch at the tip. The pods can reach up to half an inch in diameter and resemble old-fashioned pennies or silver dollars.
- Odor: When crushed, the leaves emit a distinct, pungent, sometimes garlicky, odor.
The Transformation from Weed to Cash Crop
For many years, pennycress was a problem for farmers, known for its ability to infest fields and compete with commercial crops. Its seeds can remain viable in the soil for up to 20 years, making it a persistent nuisance. The agricultural industry has, however, seen a dramatic shift in its perception and use. Projects like the Forever Green Initiative at the University of Minnesota and companies like CoverCress Inc. have domesticated pennycress, enhancing its traits for agricultural benefits.
By breeding new varieties, researchers have developed winter annual pennycress (now often called CoverCress™) that can be planted in the fall after the main harvest and harvested in the spring. This innovative approach allows farmers to grow three crops in a two-year cycle, adding a new revenue stream and intensifying land use.
The dual-purpose nature of pennycress is a key driver for its rising popularity. While providing a harvestable crop, it offers the ecosystem services of a traditional cover crop, such as:
- Erosion Control: Its root system holds soil in place during the off-season, protecting against wind and water erosion.
- Nutrient Scavenging: It absorbs leftover nutrients, like nitrogen and phosphorus, preventing them from leaching into waterways and improving water quality.
- Weed Suppression: It provides ground cover that suppresses the growth of other, more aggressive spring weeds.
- Pollinator Support: The early spring flowers provide an important source of nectar for pollinators when few other food sources are available.
Diverse Uses of Pennycress Seeds and Oil
Biofuel Production
The high oil content of pennycress seeds (up to 40%) has made it a prime candidate for biofuel production. Research has shown that pennycress oil can be converted into biodiesel and sustainable aviation fuel (SAF). The resulting biofuel has excellent cold-weather performance compared to other options, and growing it as a cash cover crop avoids direct competition with traditional food crops, a major concern with other biofuel feedstocks.
Other Industrial Applications
Beyond biofuel, the oil has potential for biodegradable packaging and industrial lubricants. The remaining seed meal, after oil extraction, is a source of high-protein animal feed, once bred for low glucosinolate content.
Edible and Floral Uses
Historically and for foragers, pennycress has had a few specific uses:
- Edible Leaves and Pods: Young, tender leaves can be added sparingly to salads for a peppery kick. The immature green seedpods can also be eaten. However, older leaves become pungent and are best avoided.
- Mustard Substitute: The seeds can be ground to create a mustard spice.
- Floral Arrangements: The distinctive silvery, coin-like seedpods and branching stems are valued in dried floral arrangements and bouquets.
Comparing Pennycress and Lookalikes
When foraging or gardening, it is important to correctly identify pennycress to avoid lookalikes, particularly Shepherd's Purse. The most reliable distinguishing features are the seedpods and overall plant structure.
| Feature | Pennycress (Thlaspi arvense) | Shepherd's Purse (Capsella bursa-pastoris) |
|---|---|---|
| Seedpod Shape | Flat, round, with a notch at the tip. | Flat, triangular or heart-shaped. |
| Seedpod Size | Larger (10–15 mm wide). | Smaller (up to 9 mm wide). |
| Seedpod Quantity | Contains multiple seeds per pod. | Contains only two seeds per pod. |
| Flower Stalks | Branched, with leaves clasping the stem. | Mostly leafless and unbranched. |
| Odor | Distinctive garlicky odor when crushed. | No specific odor when crushed. |
Potential Risks and Cultivation Considerations
While domesticated varieties are being developed, wild pennycress presents some risks, especially to livestock. The plant contains glucosinolates, which can be toxic if consumed in large quantities. This can also taint the milk of cows that have grazed on it, giving it an unpleasant flavor. For this reason, grazing is often not recommended in areas with significant pennycress growth. In gardens, its prolific seeding and long seed viability can make it a persistent weed, though it can be controlled with hand-pulling or mulching before seed set. For farmers cultivating it as a cash crop, ongoing research focuses on managing dormancy and preventing weed traits.
Conclusion: A Weed with Unprecedented Potential
Pennycress, a plant once primarily known as an agricultural pest, is now a symbol of sustainable innovation. Through dedicated research and genetic improvement, it has transitioned from a discarded roadside weed into a promising cash cover crop with numerous applications. Its journey highlights how even the most overlooked plants can hold significant value for the future of sustainable agriculture, biofuel production, and environmental health. With its ability to produce oil-rich seeds on fallow cropland while also improving soil quality, pennycress is a testament to the untapped potential that exists in the natural world. Continued research and commercial adoption will likely see pennycress play an increasingly important role in regenerative farming practices for years to come. The work of the University of Minnesota Forever Green Initiative exemplifies this promising path toward a more sustainable future.
