Bird's-foot trefoil (Lotus corniculatus)

Synonyms: Lotus caucasicus, Lotus corniculatus var. arvensis, Lotus corniculatus var. major, Lotus ambiguus

Common Names: bird's-foot deervetch, eggs and bacon, cat's clover, crowtoe, ground honeysuckle

Description:

Bird's-foot trefoil (Lotus corniculatus L.) is a low, sprawling perennial in the pea family, brought to North America from Europe, Asia, and North Africa as a forage and erosion-control plant [1][2]. It has since escaped into roadsides, old fields, and prairies, where it forms dense mats that crowd out native plants [3][4]. MISIN tracks it because it is hard to remove once established and can take over open natural areas.

Habit:

Bird's-foot trefoil grows as a low, sprawling mat of bluish-green, clover-like leaves, with stems that trail along the ground and rise up at the tips, usually 6 to 24 inches tall [6]. In summer it produces small, flat-topped clusters of bright yellow, pea-like flowers, sometimes streaked with red [4][6]. Its most reliable clue comes after the flowers fade: slender seed pods form in clusters that splay outward like the toes of a bird's foot ? the trait that gives the plant its name [4]. It is easiest to spot from June through August, when the yellow flowers stand out along roadsides and in open fields [4].

At-a-glance cues:

1. Clusters of slender brown seed pods that splay out like the toes of a bird's foot [4]
2. Bright yellow, pea-like flowers in small flat-topped clusters, sometimes streaked red, blooming May through August [4]
3. Each leaf has five leaflets ? three at the tip and two more down near the stem [6]
4. Low, sprawling stems that are nearly square in cross-section and root where they touch the ground [6]

Leaves:

1. Arranged alternately along the stem [6]
2. Compound, with five leaflets ? three at the tip and two smaller ones near the base of the leaf stalk [6]
3. Leaflets oval to spoon-shaped, with smooth (untoothed) edges and a pointed tip [6]
4. Bluish-green in color, roughly ? to ? inch long [6]

Stems:

1. Herbaceous (not woody); a perennial that resprouts each year from a deep taproot [6]
2. Low and sprawling to ascending, rising at the tips and rooting where the nodes touch the ground [6]
3. Nearly square or angled in cross-section [6]
4. Mostly smooth, sometimes slightly hairy; much-branched from the base [6]
5. Typically 6 to 24 inches long [6]

Flowers:

1. Bright yellow and pea-like, about ? inch long, sometimes tinged or streaked with red [4][6]
2. Borne in flat-topped clusters of 3 to 12 flowers at the end of a long stalk [6]
3. Bloom from May through August [4]
4. Perfect flowers (each has both male and female parts) [6]

Fruit and seeds:

1. Slender pods about 1 inch long, ripening from brown to nearly black [4]
2. Borne in clusters that splay outward like the toes of a bird's foot ? the plant's signature feature [4]
3. Each pod holds up to about 25 seeds and splits open to fling them out [4]
4. A single plant is a heavy seed producer ? roughly 375,000 seeds per pound, which build a long-lived seed bank in the soil [3]

Habitat:

Bird's-foot trefoil is native to temperate Europe, Asia, and North Africa [1][2]. It was introduced across North America for livestock forage and to hold soil along roadsides, and it now grows in most of the United States and in Canada [1][8]. It spreads into roadsides, old fields, prairies, and other open, disturbed ground [3][4]. The plant thrives in full sun and handles a wide range of soils ? dry or poorly drained, acidic or limy ? though it does poorly in deep shade and cannot survive long flooding [3].

Reproduction:

Bird's-foot trefoil spreads mainly by seed. Seeds travel on mowers and other equipment, in moving water, on animals, and on shoes and clothing ? so the plant often arrives along mowed roadsides and trails [4]. Its sprawling stems can also root where they touch the ground, letting a single plant creep outward and form a wider mat [6].

The plant is a heavy seed producer ? about 375,000 seeds per pound ? and many seeds are "hard," staying dormant in the soil for years before sprouting, which builds a stubborn seed bank [3]. For control, timing matters: the pods form and ripen through the summer, so removing plants before the pods develop is the best way to stop new seed [4]. Because it was planted on purpose for forage and erosion control, it can also spread from nearby plantings into natural areas [8].

Impact and Damage:

All parts of bird's-foot trefoil can be harmful if eaten in large amounts [5]. The plant contains cyanogenic compounds (chemicals that release cyanide when leaves or stems are crushed or chewed), which pose a low but real risk to grazing pets and livestock; serious poisoning is rare, and some plants carry little of these compounds [7][5]. Handling the plant is not dangerous, but keep large quantities away from animals that might graze on it.

In gardens and open ground, bird's-foot trefoil forms dense mats that shade and crowd out other plants, so it can take over a lawn edge, meadow, or planting bed [4]. In natural areas it is most damaging in prairies, where those same mats push out native wildflowers and grasses and degrade habitat [3][4]. It is especially hard to manage with prescribed fire ? burning actually increases its seed germination, helping it rebound after a burn that was meant to control it [3]. As a member of the pea family, it also adds nitrogen to the soil, which can shift conditions in favor of other weeds [3].

Similar species:

Several low-growing, yellow-flowered legumes are mistaken for bird's-foot trefoil. The surest way to tell it apart is its cluster of slender seed pods splayed like a bird's foot, paired with leaves that have three leaflets at the tip and two more near the stem [4][6].

Black medic (Medicago lupulina) is a common lawn look-alike with the same low, sprawling habit, but its tiny yellow flowers sit in tight little round heads rather than open flat-topped clusters, and it forms small coiled black pods instead of splayed bird's-foot pods [6].

Yellow sweetclover (Melilotus officinalis) shares the yellow pea-like flowers but stands tall and upright, often 3 to 6 feet, with flowers in long slender spikes rather than flat clusters, and it gives off a sweet hay smell when cut [6].

Hop clover (Trifolium campestre) also has small yellow flowers, but they sit in rounded heads that turn papery and brown as they age ? like tiny dried hops ? and it has true three-part clover leaves without the extra pair of leaflets near the stem [6].

Big trefoil (Lotus pedunculatus) is a close cousin with nearly identical bird's-foot pods, but it grows in wetter ground, has hollow stems, spreads by underground runners, and usually carries more flowers per cluster [3].

Monitoring and rapid response:

Signs to watch for:

1. Bright yellow, flat-topped flower clusters in open, sunny spots from late spring through summer [4]
2. Low, sprawling mats of bluish-green, clover-like leaves crowding out lawn or meadow plants [6]
3. Clusters of slender seed pods splayed like a bird's foot in late summer [4]

What you can do:

1. For small patches, dig out the whole plant ? including the deep taproot ? with a garden fork when the soil is moist [5]. Do this before the pods form in summer so the plant cannot set seed [4].
2. Bag and dispose of any plants that already carry pods, rather than composting them, so seeds do not spread [4].
3. In lawns, mowing close (under 2 inches) and repeatedly over several years gradually weakens it [5].
4. For natural area crews: target small, outlying patches first before they grow together, and plan repeat visits across the season ? one removal is rarely enough because of the long-lived seed bank [3][4].

When to call a professional:

1. Large or well-established infestations, especially in prairies, where the plant resists hand-pulling and where prescribed burning can make it worse [3]
2. Roadside or right-of-way populations that need coordinated, larger-scale treatment
3. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. USDA NRCS Plants Database. Lotus corniculatus L. plants.usda.gov
2. Plants of the World Online (Kew). Lotus corniculatus L. powo.science.kew.org
3. IUCN Global Invasive Species Database. Lotus corniculatus. iucngisd.org
4. Minnesota Department of Natural Resources. Birdsfoot trefoil (Lotus corniculatus). dnr.state.mn.us
5. King County Noxious Weeds (Washington). Birdsfoot trefoil identification and control. kingcounty.gov
6. Penn State Extension. Lawn and Turfgrass Weeds: Birdsfoot Trefoil (Lotus corniculatus L.). extension.psu.edu
7. Scriber JM. "Cyanogenic glycosides in Lotus corniculatus: their effect upon growth, energy budget, and nitrogen utilization of the southern armyworm." Oecologia. semanticscholar.org
8. University of Minnesota Extension. Birdsfoot trefoil. extension.umn.edu

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