Black medic (Medicago lupulina)

Synonyms: Melilotus lupulinus, Trifolium lupulinum, Medicago lupulina var. willdenowii

Common Names: Hop clover, yellow trefoil, nonesuch, black medick

Description:

Black medic (Medicago lupulina) is a low, sprawling, clover-like plant in the pea family, native to Europe, temperate Asia, and North Africa [1][2]. It was brought to North America in the 1700s as a forage and soil-building plant and is now a common weed of lawns, gardens, and disturbed ground, especially on dry, compacted, low-fertility soil [2][4]. MISIN tracks it because it spreads readily by seed and forms patches in thin turf and bare ground, though it is a minor nuisance weed rather than a serious threat to natural areas [2].

Habit:

Black medic is a low, trailing plant that hugs the ground, with stems that sprawl out from a central taproot [3]. Its leaves look much like clover ? three small oval leaflets ? but with a tell-tale difference: the middle leaflet sits on a short stalk of its own, and each leaflet has a tiny point at its tip [2][3]. From late spring through summer it carries small, round clusters of tiny bright-yellow flowers [2]. As the flowers fade, each cluster is replaced by a tight bundle of small seed pods that coil up and turn black when ripe ? the source of the name "black medic" [2]. It is easiest to recognize in summer, when the yellow flower clusters and, later, the little black coiled pods are present [2].

At-a-glance cues:

1. Low, sprawling, clover-like plant with three small oval leaflets [2][3]
2. Middle leaflet on a short stalk of its own, and each leaflet tipped with a tiny point [2][3]
3. Small, round clusters of bright-yellow flowers, late spring through summer [2]
4. Tightly coiled seed pods that turn black when ripe [2]

Leaves:

1. Arrangement: alternate, compound with three leaflets (trifoliate), like clover [2]
2. Leaflets: small and oval, the middle one on a short stalk of its own; each tipped with a tiny point [2][3]
3. Margin: finely toothed near the tip [2]
4. Surface: dark green, with fine hairs [2]

Stems:

1. Habit: low, sprawling annual (sometimes a short-lived perennial), trailing along the ground, to about 1.5 feet long [2]
2. Surface: light green to reddish-green, covered in fine white hairs [2]
3. Roots: grows from a taproot; as a legume, it fixes nitrogen in root nodules [2][3]

Flowers:

1. Color: bright yellow [2]
2. Shape: tiny pea-like flowers packed into small, round clusters about 1/4 inch across (15 to 20 flowers each) [2]
3. Arrangement: clusters on short stalks from the leaf joints [2]
4. Bloom time: late spring through summer [2]

Fruit and seeds:

1. Fruit: each flower cluster becomes a dense bundle of small, kidney-shaped pods that coil tightly and turn black when ripe [2]
2. Each pod holds a single seed [2]
3. Reproduction is by seed only; a plant can set many seeds [2]
4. Seeds spread in soil, in crop seed, on mowing equipment, and on shoes and animals [2]

Habitat:

Black medic is native to Europe, temperate Asia, and North Africa [1][2]. In North America it is not native; it was introduced in the 1700s as a forage and soil-improving plant and is now widespread across the continent [2][4]. It grows in open, sunny, disturbed ground and is most common in dry, compacted, low-fertility soil ? lawns, gardens, roadsides, railways, cropland, pastures, and waste areas [2]. In lawns it often signals thin, under-fertilized turf, since it competes well where grass is weak [2].

Reproduction:

Black medic spreads only by seed, and a single plant can set many [2]. The seeds move in soil, mixed with crop seed, and on mowing equipment, shoes, and animals, so it turns up readily in disturbed ground and thin lawns [2]. As a legume, it pulls nitrogen from the air through its roots, which lets it thrive on poor soils where grasses struggle [2][3].

It usually behaves as an annual ? sprouting, flowering, and setting seed in one season ? though it can persist a little longer in mild spots [2][3]. It flowers and sets seed through the summer [2]. For control timing: pull plants or cut the flower clusters before the pods ripen and blacken, so they cannot reseed [2].

Impact and Damage:

Black medic is mainly a lawn and garden nuisance rather than a health hazard ? it is not toxic. In turf it forms low, sprawling patches that crowd out thin grass and look weedy, and it is most troublesome on dry, compacted, or under-fertilized lawns [2]. It can also turn up as a minor weed in gardens, crops, and disturbed ground [2].

Its broader effect on natural areas is limited; it is a weed of lawns, fields, and disturbed places rather than a strong invader of intact habitats [2]. As a nitrogen-fixing legume it can even add nitrogen to poor soil, and it has been grown as a forage and cover plant ? so in some settings it is more nuisance than threat [2].

Similar species:

Black medic is most often confused with clovers and with yellow woodsorrel, which share its low, three-leaflet look.

Hop clover (Trifolium dubium) is the closest match, a small lawn clover with the same little round clusters of yellow flowers. Tell them apart by black medic's tiny coiled black pods and the small stalk and point on its middle leaflet, which hop clover lacks [2].

White clover (Trifolium repens) has the same three-leaflet clover look but bears white (not yellow) flowers, and its leaflets are stalkless and lack black medic's tiny tip point [2].

Yellow woodsorrel (Oxalis stricta) also grows low with three leaflets and yellow flowers, but its leaflets are heart-shaped (notched at the tip) and its flowers have five separate petals rather than black medic's tight clover-like clusters [2][3].

Monitoring and rapid response:

Signs to watch for:

1. Low, sprawling, clover-like patches with small round clusters of yellow flowers in summer, especially in thin or dry lawns [2]
2. Three oval leaflets with the middle one on a short stalk and a tiny point at each tip [2][3]
3. Tight bundles of small coiled pods that turn black when ripe [2]

What you can do:

1. Pull plants by hand, especially after rain when the soil is soft and the taproot lifts more easily; do it before the pods ripen and blacken [2]
2. Cut or mow off the flower clusters before they set seed [2]
3. Crowd it out by keeping turf dense and healthy ? mow higher, fertilize thin lawns, and ease soil compaction with aeration, since black medic favors weak, dry, low-nitrogen turf [2][3]
4. Bag and trash plants that already have ripe pods rather than composting them [2]
5. For garden beds and larger patches, repeat removal through the season and over the next year to catch new seedlings [2]

When to call a professional:

1. Widespread infestations across large lawns or fields where hand methods cannot keep up [2]
2. 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. Plants of the World Online (POWO), Royal Botanic Gardens, Kew. Medicago lupulina L. powo.science.kew.org
2. University of Wisconsin?Madison Division of Extension. Black Medic, Medicago lupulina. hort.extension.wisc.edu
3. Penn State Extension. Lawn and Turfgrass Weeds: Black Medic (Medicago lupulina L.). extension.psu.edu
4. USDA NRCS PLANTS Database. Medicago lupulina L. plants.usda.gov

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