London rocket (Sisymbrium irio)
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London rocket is a highly competitive winter annual broadleaf plant. In California it is found in primarily in the lower two thirds of the state but has also been reported in upper central valley to about 2600 feet (800 m).
Roadsides, fields, orchards, vineyards, gardens, and other disturbed sites.
Cotyledons (seed leaves) are oval, about 1/13 to 1/4 of an inch (2–6 mm) long, hairless, and on stalks that are equal in length to the blade. The first leaf is oval, a bit larger than the cotyledon, has smooth edges or a few weak teeth, and is on a long stalk. The next few leaves resemble the first, but have shallow-toothed edges. Leaves are alternate to one another along the stem.
Plants exist as rosettes until they develop flowering stems at maturity.
Stems are erect, mostly branch near the base, and usually grow to about 2 feet (60 cm) tall. Leaves are nearly hairless. Rosette leaves vary from deeply lobed to being separated fully into leaflets (compound) in the lower part. Lower leaves can grow to about 6 inches (15 cm) long. Upper leaves are somewhat oblong, mostly with two basal lobes angled away from the base, stalkless, smaller than the lower leaves, and do not clasp the stem. Sisymbrium mustards like London rocket and tumble mustard have simple hairs, rather than the branched hairs of flixweed. Flixweed has very finely divided leaves whose leaflets are also finely divided once or twice again. However, most Sisymbrium species have undivided, lobed leaves or leaves divided into leaflets that may be lobed, but are not divided again.
Flowering takes place from January to May. Flowers are pale yellow, rarely white, narrowed at the base, and roughly 1/10 to 1/6 inch (3–4 mm) long. Small clusters of flowers grow at the stem tip.
Fruits consist of long, thin, tubular seed pods, that are flexible, straight or slightly curved, roughly 1 to 1-1/2 inches (3-4 cm) long, and about 1/25 of an inch (1 mm) wide.
Seeds are oblong and less than 1/25 inch (1 mm) long.
London rocket reproduces by seed.