T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network

Sisymbrium officinale (Hedge mustard)

Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Rosids
Order: Brassicales
Family: Brassicaceae
Genus: Sisymbrium
Species: S. officinale
Binomial name: Sisymbrium officinale
Synonym:  Erysimum officinale
Common names: Hedge mustard, Common Hedge mustard, English watercress, Hairypod, Tumbling mustard, Oriental mustard, Wild mustard, Indian hedge mustard, Oriental rocket mustard, Oriental rocket, Erysimum, Thalictroc

Sisymbrium officinale is a plant in the family Brassicaceae. It is an annual or biennial herb with a rosette or deeply divided leaves with toothed margins and with a much larger rounded terminal lobe that grows to 90cm high. It is a native of Europe and North Africa, and it is now well-established throughout the world. 
Sisymbrium officinale is a common weed of wasteland, roadsides, cultivation and disturbed habitats and is suspected of tainting milk. Apart from problems with competition, hedge mustard can also be a concern in crops such as peas because its tough stem material can clog up harvesters.
In New Zealand it normally it germinates either in spring or autumn. Basal leaves form a deeply divided rosette (a cluster of leaves at the base of a plant often lying flat against the ground). The basal (lower) leaves are up to 10cm long, pinnatisect (cut into lobes on both sides of the midrib to or almost to the midrib) with 3-5 pairs of toothed lobes and a large terminal lobe petiolate (with a leaf stalk). Middle and upper stem leaves are smaller, with or without a short petiole, much less divided, alternate (1 leaf per node). The whole plant often appears grey-green in appearance.

The stem is tall, erect, wiry and with very short internodes. It is usually short-haired, sometimes glabrous. 
The small pale yellow terminal flowers are in racemes (a simple inflorescence in which the flowers are stalked) with four yellow to pale yellow petals that are 2-4mm long, in the shape of a cross. The inflorescence has no bracts. There are 4 free sepals that are 2mm long, 4-6 stamens, the inner four being longer than the outer pair. 
The fruits are a conically shaped siliqua (a dry dehiscent fruit three times as long as broad) 1-2cm long, without a beak, held close to the stem on a short stout pedicel (stalk) 1-2mm long. It is dehiscent (opens at maturity to release the contents) with 2 valves, each with several seeds which are about 1.5mm long.

Spreading flower clusters.

A young flower cluster.

A deeply-lobed leaf.

The underside of a leaf.

The roughly hairy stems with purple patches at the nodes.

Thanks to Wikipedia for text and information: https://creativecommons.org/licenses/by-sa/3.0/