Creeping yellowcress (Rorippa sylvestris)

Synonyms: Sisymbrium sylvestre, Nasturtium sylvestre

Common Names: Yellow fieldcress, keek

Description:

Creeping yellowcress (Rorippa sylvestris) is a low, yellow-flowered perennial in the mustard family, native to Europe and southwest Asia [3][4]. It spreads by creeping white underground roots ? and by tiny root fragments ? which makes it very hard to get rid of once it takes hold [2][3]. MISIN tracks it because it is a tenacious weed of wet and disturbed ground that often arrives hidden in the roots of nursery plants such as hostas and daylilies [2].

Habit:

Creeping yellowcress is a low, branching perennial, usually under about a foot tall, with stems that often sprawl at the base before turning upward [3]. Its leaves are deeply cut into lobed, toothed segments, giving them a feathery, divided look, and they are largest toward the base of the plant [1][3]. In late spring and summer it produces elongated clusters of small, bright-yellow, four-petaled flowers, each about a quarter inch across, followed by slender pods that angle up and out from the stem [1][3]. Below ground is the key feature: white, fleshy, horizontally creeping roots that send up many new plants [2].

It is easiest to spot in late spring and summer, when the yellow flowers and slender pods are present on damp, disturbed ground [1]. Year-round, the giveaway is the white, spreading underground roots ? unlike its native yellowcress relatives, which grow from a single taproot [2].

At-a-glance cues:

1. Small, bright-yellow, four-petaled flowers in elongated clusters, late spring?summer [1][3]
2. Deeply lobed, toothed, feathery leaves, largest toward the base [1][3]
3. Slender seed pods (about ? inch) angling up and out from the stem [1]
4. White, fleshy, horizontally creeping underground roots that sprout new plants [2]

Leaves:

1. Arrangement: alternate along the stem [3]
2. Shape: deeply cut (pinnately lobed) into toothed segments, giving a feathery look; lower leaves largest, up to several inches long [1][3]
3. Margin: lobed and toothed [1][3]
4. Surface: smooth (hairless) [3]

Stems:

1. Habit: a herbaceous (non-woody) perennial, usually under about a foot tall, the stems often sprawling at the base then turning upward and branching [3]
2. Roots: white, fleshy, horizontally creeping underground roots that produce many new plants ? the defining feature [2]

Flowers:

1. Color: bright yellow [1][3]
2. Shape: small (about ? inch / 4?5 mm across), with four petals, the petals about twice as long as the sepals [1][3]
3. Arrangement: in elongated clusters at the ends of branching stems [1]
4. Bloom time: late spring through summer [1]

Fruit and seeds:

1. Fruit type: a slender pod (silique), about ? inch (10?25 mm) long, angling up and out from the stalk [1][3]
2. Seeds: many tiny seeds per pod [3]
3. Dispersal: by seed, and ? most importantly ? by creeping roots and small root fragments that each grow into a new plant [2]

Habitat:

Creeping yellowcress is native to Europe and southwest Asia and was introduced to North America, where it is now widely naturalized [3][4]. It is thought to have arrived with imported herbaceous perennials ? especially hostas and daylilies ? with root fragments tangled in the nursery stock [2].

It is a plant of wet and disturbed ground. Look for it on muddy or grassy ditch and pond margins, in soggy meadows and floodplains, on river and lake shores, in poorly drained spots, and in gardens, nursery fields, and other disturbed, damp sites [1][3].

Reproduction:

Creeping yellowcress spreads two ways, and the underground one is what makes it such a problem. It sets seed in slender pods, but its main mode of spread is by white, fleshy roots that creep sideways underground and push up new plants ? and even a root fragment less than an inch long can grow into a new plant [2]. This is exactly how it reaches new gardens: small root pieces ride along in the soil and roots of nursery plants like hostas and daylilies, then sprout where those plants are planted [2].

Because of those creeping roots, digging and tilling can backfire by chopping the roots into fragments that each resprout ? which is why simple physical removal often makes infestations worse rather than better [2][3]. For control, the key points are to remove every root piece when plants are still small, to avoid tilling an infested area, and to inspect new nursery plants before planting them [2].

Impact and Damage:

For homeowners and gardeners, creeping yellowcress is a stubborn landscape weed rather than a health hazard. It is not known to be toxic to people or pets. The trouble is how hard it is to remove: it regrows from root fragments left in the soil, and it often arrives unnoticed in the roots of new nursery plants, then spreads through a bed or lawn [2][3].

For natural area stewards, creeping yellowcress is a persistent invader of wet, open ground. Its creeping roots let it form spreading patches in soggy meadows, floodplains, ditches, and shorelines, where it can crowd out other low plants, and it is widely described as extremely difficult to eradicate once established [3]. Because it moves so readily in soil and nursery stock, preventing its arrival and catching new patches early are the most effective steps [2][3].

Similar species:

Creeping yellowcress can be mistaken for native yellowcresses with the same small yellow flowers. The way to separate them is below ground: creeping yellowcress has white, horizontally spreading roots, while the native species grow from a single taproot [2].

Marsh yellowcress (Rorippa palustris) is a native yellowcress of the same wet places and is worth keeping rather than removing. It is told apart by its single white taproot ? it lacks the creeping, spreading underground roots of creeping yellowcress ? and by its shorter, plumper seed pods [2][3]. Very young plants of the two can be nearly impossible to tell apart until the roots develop [2].

Monitoring and rapid response:

Signs to watch for:

1. Low, branching plants with feathery, deeply lobed leaves on damp, disturbed ground [1][3]
2. Elongated clusters of small, bright-yellow, four-petaled flowers in late spring and summer, with slender pods [1]
3. White, fleshy, horizontally creeping roots when you dig at the base [2]
4. New plants appearing in a bed after planting nursery-grown hostas or daylilies [2]

What you can do:

1. Dig out plants while they are still small, carefully lifting and removing every piece of the white creeping root ? fragments left behind regrow [2]
2. Avoid rototilling an infested area, which chops the roots into pieces that each sprout a new plant [2][3]
3. Bag and dispose of all dug material rather than composting it or leaving it on the soil [2]
4. Inspect and, if possible, wash the roots of new nursery plants (especially hostas and daylilies) before planting, and watch those spots for sprouts [2]
5. Smother a patch by covering it with cardboard or heavy mulch through a full growing season where digging is impractical [2]
6. For natural areas, crews can target small outlier patches first, remove all root pieces over repeat visits, and avoid moving infested soil to new sites [2][3]

When to call a professional:

1. Large or well-established patches where hand-digging cannot keep up with the creeping roots [2][3]
2. Sites where it keeps returning from root fragments despite removal [2][3]
3. Wet meadow, ditch, or shoreline sites where work may need special care and permits [3]
4. 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. Rorippa sylvestris (L.) Besser. plants.usda.gov
2. North Carolina State Extension Gardener Plant Toolbox. Rorippa sylvestris (Creeping Yellowcress). plants.ces.ncsu.edu
3. Native Plant Trust, Go Botany. Rorippa sylvestris (creeping yellow-cress). gobotany.nativeplanttrust.org
4. Plants of the World Online (POWO), Royal Botanic Gardens, Kew. Rorippa sylvestris (L.) Besser. powo.science.kew.org

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