Indian mustard

Brassica x juncea
infestation in flower along a rural roadside (Photo: Sheldon Navie)
habit (Photo: Sheldon Navie)
large lower leaves forming a loose basal rosette (Photo: Sheldon Navie)
close-up of mostly hairless stem and leaf stalk (Photo: Sheldon Navie)
close-up of lower leaf (Photo: Sheldon Navie)
close-up of leaf underside (Photo: Sheldon Navie)
bluish-green stems and upper leaves (Photo: Sheldon Navie)
smaller and narrower uppermost leaf (Photo: Sheldon Navie)
elongating flower cluster (Photo: Sheldon Navie)
close-up of bright yellow flowers (Photo: Sheldon Navie)
mature fruit (Photo: Sheldon Navie)
young plants (Photo: Sheldon Navie)
Herb
Alternate
Simple
Yellow
Bluish-green
Green

A short-lived herbaceous plant with upright stems growing up to 1.8m tall. Its leaves are initially borne in a rosette at the base of the plant and are later alternately arranged along the stems. Its lower leaves are relatively large (up to 30 cm long and 15 cm wide) and deeply lobed while its upper leaves are smaller and elongated in shape. Its yellow flowers are arranged in elongating clusters at the tips of the branches. Its elongated fruit (2-6 cm long and 2-5 mm wide) have two compartments and end in a tapering 'beak' 4-10 mm long.

Common names 
Also known as: Indian mustard, brown mustard, Chinese mustard, gai choy, leaf mustard, oriental mustard,
Family 
Brassicaceae
Deciduous 
No
Flowering time 
Spring - Summer
Native/Exotic 
Exotic
Origin 
Native to central and eastern Asia.
Notifiable 
No
Council declaration 
SIL – Special Investigation List
Known distribution 

Widely naturalised in south-eastern Queensland, but mainly found in the southern parts of the region (i.e. in the Moreton and Darling Downs districts). Also scattered in other parts of central and northern Queensland. Widely naturalised in other parts of Australia (i.e. in New South Wales, the southern parts of the Northern Territory, many parts of Western Australia, and south-eastern South Australia). Also naturalised on Norfolk Island, and sparingly naturalised in Victoria and Tasmania.

Habitat 

A weed of crops and fallows, pastures, disturbed sites, waste areas, roadsides, railway lines and riparian vegetation.

Habit 

A short-lived (i.e. annual) herbaceous plant with upright (i.e. erect) stems usually growing 0.3-1 m tall, but occasionally reaching up to 1.8m in height.

Impact and control methods 
Stem and leaves 

Plants usually have several upright (i.e. ascending) branches, mostly towards the top of the plant. Younger stems are hairless (i.e. glabrous) or somewhat hairy (i.e. pubescent) and are either green or bluish-green (i.e. glaucous) in colour. The leaves are initially borne in a rosette at the base of the plant (i.e. basal rosette) and are later alternately arranged along the upright stems. The basal leaves are relatively large (up to 30 cm long and 15 cm wide) and borne on stalks (i.e. petioles) 2-8 cm long. They are deeply lobed, with the uppermost lobe being much larger (i.e. they are lyrate and pinnatifid or pinnatisect). The lower stem leaves are similar, but the leaves reduce in size towards the top of the stems and become less lobed. The uppermost leaves are usually entire, almost stalkless (i.e. sub-sessile) and elongated in shape (i.e. lanceolate or linear). All leaves are green or bluish-green (i.e. glaucous) in colour and sparsely hairy (i.e. hispid).

Flowers and fruits 

The yellow flowers are arranged in elongating clusters at the tips of the branches (i.e. terminal racemes) and are borne on stalks (i.e. pedicels) 5-20 mm long. These flowers have four narrow sepals (3.5-7 mm long and 1-1.7 mm wide) and four larger petals (6.5-13 mm long and 5-7.5 mm long) with rounded tips. They also have six stamens, consisting of stalks (i.e. filaments) 4-7 mm long and yellow anthers (1.5-2 mm long), and an ovary topped with a rounded stigma. Flowering occurs mostly during spring and early summer (i.e. from September to December). The elongated fruit resembles a pod (i.e. it is a siliqua) and is borne in an upright (i.e. ascending) or spreading position. These fruit (2-6 cm long and 2-5 mm wide) have two compartments, each containing 6-15 seeds, and end in a tapering 'beak' 4-10 mm long. They turn from green to pale brown or straw-coloured as they mature. The seeds are egg-shaped (i.e. ovoid) or almost rounded (1-2.5 mm long), have a finely pitted (i.e. minutely reticulate) surface, and are brown or grey in colour. Fruit are present mainly during summer (i.e. from December to January).

Reproduction and dispersal 

This species reproduces only by seed, which are often spread in contaminated agricultural produce. They may also be dispersed by wind, water and human activities (e.g. by roadside slashers and in contaminated soil).

Similar species 

Indian mustard (Brassica × juncea) is similar to canola (Brassica × napus), wild turnip (Brassica tournefortii), turnip weed (Rapistrum rugosum), charlock (Sinapis arvensis) and Buchan weed (Hirschfeldia incana). These species canbe distinguished from eash other by the following differences: Indian mustard (Brassica × juncea) has mostly hairless (i.e. glabrous) stems and pale yellow or bright yellow flowers with moderately large petals (6.5-13 mm long). Its fruit very are elongated in shape (2-6 cm long and 2-5 mm wide) with a relatively short beak (4-10 mm long) at the tip. These fruit are borne on moderately long stalks (i.e. pedicels), 7-20 mm long, and are held in an upright (i.e. ascending) or spreading position.canola (Brassica × napus) has hairless (i.e. glabrous) stems and pale yellow or bright yellow flowers with relatively large petals (11-18 mm long). Its fruit are very elongated in shape (4.5-11 cm long and 2.5-4 mm wide) with a long beak (5-30 mm long) at the tip. These fruit are borne on long stalks (i.e. pedicels), 15-30 mm long, and are held in an upright (i.e. ascending) or spreading position.wild turnip (Brassica tournefortii) has bristly hairy (i.e. hispid) lower stems and pale yellow or whitish flowers with relatively small petals (5-8 mm long). Its fruit are very elongated in shape (3-7 cm long and 2-3 mm wide) with a long beak (8-20 mm long) at the tip. These fruit are borne on moderately long stalks (i.e. pedicels), 10-30 mm long, and are held in an upright (i.e. ascending) or spreading position.turnip weed (Rapistrum rugosum) has bristly hairy (i.e. hispid) stems and bright yellow flowers with moderately large petals (6-10 mm long). Its fruit are short and somewhat rounded in shape (6-10 mm long) with a short beak (3-6 mm long) at the tip. These fruit are borne on short stalks (pedicels), 2-5 mm long, and are held close (i.e. appressed) to the flowering stem.charlock (Sinapis arvensis) has bristly hairy (i.e. hispid) stems and bright yellow flowers with moderately large petals (9-12 mm long). Its fruit are very elongated in shape (2.5-5.5 cm long and 2-4 mm wide) with a long beak (10-15 mm long) at the tip. These fruit are borne on relatively short and thick stalks (i.e. pedicels), 3-7 mm long, and are held in an upright (i.e. ascending) or spreading position. Buchan weed (Hirschfeldia incana) has bristly hairy (i.e. hispid) lower stems and pale yellow flowers with relatively small petals (6-8 mm long). Its fruit are elongated in shape (7-17 mm long and 1-2 mm wide) with a short thick beak (3-6 mm long) at the tip. These fruit are borne on short thick stalks (i.e. pedicels), 2-4 mm long, are held close (i.e. appressed) to the flowering stem. It is also relatively similar to hedge mustard (Sisymbrium officinale), Indian hedge mustard (Sisymbrium orientale), London rocket (Sisymbrium irio) and African turnip weed (Sisymbrium thellungii). However, none of these species have an elongated 'beak' at the tip of their fruit.