Annual wallrocket (Diplotaxis muralis)

Synonyms: Sisymbrium murale, Brassica muralis

Common Names: Wall rocket, mustard rocket

Description:

Annual wallrocket (Diplotaxis muralis) is a small, yellow-flowered annual plant in the mustard family, native to Europe and northern Africa [1][2]. It was carried to North America in the 1800s ? partly in ship ballast and crop seed ? and spread along railways and roads, and it now grows as a weed of disturbed, open ground [2]. MISIN tracks it as a non-native species to map where it occurs; it is mainly a weed of roadsides, waste places, and cultivated ground rather than a plant that takes over healthy natural areas [1][2].

Habit:

Annual wallrocket is a low, weedy herb, usually only a few inches to about 2 feet tall (5?60 cm), often branching and sprawling [1]. Most of its leaves form a low cluster near the base of the plant, and they are lobed or toothed along the edges [1]. From spring through fall it produces small yellow flowers with four petals arranged in a cross ? the classic mustard-family flower [1]. The flowers give way to slender, upright seed pods about ? to 1? inches long (15?40 mm) with a short beak at the tip [1]. It is easiest to spot during the growing season when it is in flower and fruit on bare, dry, disturbed ground [1][2].

At-a-glance cues:

1. Small yellow flowers with four petals in a cross shape (mustard family) [1]
2. Most leaves in a low cluster at the base, lobed or toothed [1]
3. Slender, upright seed pods about ? to 1? inches (15?40 mm) long with a short beak [1]
4. A low, branching weed of dry, open, disturbed ground ? roadsides, railways, waste places, gardens [1][2]

Leaves:

1. Mostly in a low cluster (basal rosette) near the base of the plant, with fewer up the stem [1]
2. About ? to 3? inches (20?90 mm) long [1]
3. Edges lobed to toothed, sometimes nearly smooth; blades elliptic to spoon-shaped [1]

Stems:

1. Herbaceous (soft, not woody), in an annual or sometimes biennial plant [1][2]
2. Erect to spreading and branching, ranging from a couple of inches to about 2 feet tall (5?60 cm) [1]
3. Soft, herbaceous base ? unlike the firm, woody base of the perennial wall-rocket [1]

Flowers:

1. Small and yellow, with four petals arranged in a cross and six stamens [1]
2. Borne in elongating clusters at the stem tips [1]
3. Bloom from spring through fall [1]
4. Each flower has both male and female parts (perfect) [1]

Fruit and seeds:

1. Fruit is a slender, upright pod (silique) about ? to 1? inches (15?40 mm) long with a short beak at the tip [1]
2. Each pod holds two rows of seeds in each chamber [1]
3. The plant reproduces and spreads only by seed [1][2]

Habitat:

Annual wallrocket grows in dry, open, sunny, disturbed places ? roadsides, railway edges, waste ground and refuse piles, rocks, walls, gardens, and sandy soils ? and it occasionally turns up in crops and pastures [2]. It is native to central and southern Europe and northern Africa, and also occurs across parts of Asia [1][2]. It was introduced to North America in the 1800s, where it has naturalized as a weed; its spread was helped along by railways and by seed carried in ship ballast and contaminated crop seed [2]. It favors already-disturbed bare ground rather than intact natural plant communities [1][2].

Reproduction:

Annual wallrocket spreads only by seed [1]. Its seeds move in disturbed soil, on vehicles, tools, and footwear, in contaminated crop and grass seed, and ? as its history shows ? along transport corridors such as roads and railways [2]. It is an annual or biennial: a plant sprouts, flowers, sets a crop of seed, and dies within a year or two [1][2].

Because it lives and dies by its seed, the key to control is stopping seed from forming ? pull or cut plants before the slender pods ripen, and keep bare, disturbed ground to a minimum so seedlings have nowhere to take hold [1][2].

Impact and Damage:

Annual wallrocket is not poisonous to people or pets ? it is a relative of the edible salad rocket (arugula) [1]. Its significance is as a weed rather than a hazard. It establishes on disturbed, open ground and can compete with crops, garden plants, and pasture, making it a nuisance in cultivated and waste areas [2]. In natural areas its effect is limited and local: it colonizes already-disturbed, bare, or sandy spots ? roadsides, trail edges, and clearings ? rather than crowding out healthy stands of native plants [1][2]. Its main importance there is as a widespread non-native weed and an indicator of disturbed ground [1][2].

Similar species:

Annual wallrocket is one of several yellow-flowered mustards that are mixed up with one another. The low, mostly-basal lobed leaves, soft (non-woody) base, and slender short-beaked pods are the best clues.

Perennial wall-rocket (Diplotaxis tenuifolia) is the closest look-alike ? a very similar yellow-flowered relative. It is a longer-lived perennial with a firm, somewhat woody base and longer fruit stalks, while annual wallrocket is a soft-based annual or biennial [1].

Wild mustard (Sinapis arvensis), also called charlock, is a common yellow-flowered mustard weed of fields and waste ground. It is generally taller and bristly-hairy, with leafier stems rather than annual wallrocket's low rosette of leaves [1].

Yellow rocket (Barbarea vulgaris) is another yellow-flowered mustard of fields, roadsides, and damp ground. It has glossy, dark-green deeply lobed leaves and forms denser clusters of flowers, and tends to grow in moister sites than annual wallrocket [1].

Field mustard (Brassica rapa) is a taller yellow-flowered mustard weed of farm fields with clasping upper leaves that wrap the stem ? a feature annual wallrocket lacks [1].

Monitoring and rapid response:

Signs to watch for:

1. A low, branching weed with small yellow four-petaled flowers on dry, disturbed, or sandy ground [1]
2. A low cluster of lobed or toothed leaves at the base of the plant [1]
3. Slender, upright seed pods about ? to 1? inches long with a short beak, through the growing season [1]
4. Plants along roadsides, railways, waste ground, gardens, and field edges [2]

What you can do:

1. Hand-pull or hoe plants ? they are shallow-rooted and come up easily, especially when young and the soil is moist [1]
2. Remove plants before the pods ripen to stop seed from forming, and bag any seeding plants rather than leaving them on site [1][2]
3. Keep bare ground covered with mulch or healthy plantings so seedlings have nowhere to establish [1][2]
4. Clean soil and seed off tools, mowers, and vehicles before moving between areas [2]
5. Natural area crews can pull or hoe plants in disturbed spots before they set seed, focus on stopping seed production, and limit unnecessary soil disturbance that opens ground for it [1][2]

When to call a professional:

1. Large infestations in crop fields, pastures, or along rights-of-way where hand removal cannot keep up [2]
2. Persistent re-infestation from a built-up seed bank or a nearby seed source [1]
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. Native Plant Trust, Go Botany. Diplotaxis muralis (annual wall-rocket). gobotany.nativeplanttrust.org
2. Botanical Society of Britain & Ireland (BSBI). Diplotaxis muralis (Annual Wall-rocket). bsbi.org
3. USDA NRCS PLANTS Database. Diplotaxis muralis (L.) DC. (DIMU). plants.usda.gov

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