Brassica tournefortii
(African mustard)

Pictures

Picture	Title	Caption	Copyright
Title Flowers Caption Brassica tournefortii (African mustard); flowers. USA. Copyright Public Domain/released by the USDA-NRCS PLANTS Database. Original photographer, Patrick J. Alexander.	Flowers	Brassica tournefortii (African mustard); flowers. USA.	Public Domain/released by the USDA-NRCS PLANTS Database. Original photographer, Patrick J. Alexander.
Title Flowers Caption Brassica tournefortii (African mustard); flowering habit. Carmel Mountain Preserve, northern San Diego, California, USA. March, 2009. Copyright Public Domain/released by 'Stickpen', via wikipedia	Flowers	Brassica tournefortii (African mustard); flowering habit. Carmel Mountain Preserve, northern San Diego, California, USA. March, 2009.	Public Domain/released by 'Stickpen', via wikipedia
Title Basal rosette Caption Brassica tournefortii (African mustard); habit, showing basal rosette. Under favourable conditions, the rosette can reach 100cm in diameter. Hedgepeth Hills, Maricopa County, Arizona, USA. February, 2008. Copyright ©Michael J. Plagens-2008/via wikipedia - CC BY-SA 4.0	Basal rosette	Brassica tournefortii (African mustard); habit, showing basal rosette. Under favourable conditions, the rosette can reach 100cm in diameter. Hedgepeth Hills, Maricopa County, Arizona, USA. February, 2008.	©Michael J. Plagens-2008/via wikipedia - CC BY-SA 4.0
Title Leaf Caption Brassica tournefortii (African mustard); close view of leaf. Big Bend of the Colorado State Recreation Area, Nevada, USA. Copyright ©Bonnie Million/National Park Service/Bugwood.org - CC BY-NC 3.0 US	Leaf	Brassica tournefortii (African mustard); close view of leaf. Big Bend of the Colorado State Recreation Area, Nevada, USA.	©Bonnie Million/National Park Service/Bugwood.org - CC BY-NC 3.0 US
Title Seedpods Caption Brassica tournefortii (African mustard); seedpods. USA. Copyright Public Domain/released by the USDA-NRCS PLANTS Database. Original photographer, Patrick J. Alexander.	Seedpods	Brassica tournefortii (African mustard); seedpods. USA.	Public Domain/released by the USDA-NRCS PLANTS Database. Original photographer, Patrick J. Alexander.
Title Seeds Caption Brassica tournefortii (African mustard); seeds. Note scale. USA. Copyright Public Domain - Released by the USDA-NRCS PLANTS Database/Original photographer, Steve Hurst	Seeds	Brassica tournefortii (African mustard); seeds. Note scale. USA.	Public Domain - Released by the USDA-NRCS PLANTS Database/Original photographer, Steve Hurst

Identity

Preferred Scientific Name

• Brassica tournefortii Gouan

Preferred Common Name

• African mustard

Other Scientific Names

• Brassica amblyorhyncha Coustur. & Gand
• Brassica mesopotamica (Spreng.) Bernh
• Brassica sisymbrioides (Fisch. ex DC.) Grossh
• Brassica stocksii Hook.f. & Thomson
• Brassicella cheiranthus sensu Adamson
• Coincya tournefortii (Gouan) Alcaraz & al.
• Eruca erecta Lag.
• Erucastrum minutiflorum Pau & Font Quer
• Erucastrum tournefortii (Gouan) Link
• Sinapis caspica Willd. ex Ledeb.

International Common Names

• English: Asian mustard; long-fruit turnip; Mediterranean mustard; Mediterranean turnip; pale cabbage; Sahara mustard; tournefort’s birdrape; tournefort’s mustard; wild turnip
• Spanish: mostaza; mostaza del desierto; mostaza del Sahara
• French: chou de tournefort
• Arabic: qarras; shiltam

Local Common Names

• Finland: välimerenkaali
• Italy: cavolo di tournefort
• UK: bresychen welw

Summary of Invasiveness

B. tournefortii is a widespread species of mustard, commonly known as African mustard or Sahara mustard. Native to Africa, Asia and Europe, it has spread globally and naturalised in North America, Australia and New Zealand. It is a highly invasive annual herb and is recorded as negatively affecting native species in some US states and Australia. Its fast growth rates enable it to monopolize soil moisture and light and mature before native wildflowers. B. tournefortii is often the dominant species in areas of usually diverse flora. CalEPPC (1999) lists the species as ‘regionally most invasive wildland pest plant’. Some factors may increase its invasive capability, for example in the western Sonoran Desert of California, USA, B. tournefortii quickly invaded areas of natural disturbance where soils were young while older geological surfaces were less vulnerable to invasion. Another study in New South Wales, Australia, found that rabbit mounds enhanced the germination of B. tournefortii seeds. 

Taxonomic Tree

• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Dicotyledonae
•                     Order: Capparidales
•                         Family: Brassicaceae
•                             Genus: Brassica
•                                 Species: Brassica tournefortii

Notes on Taxonomy and Nomenclature

Brassica tournefortii is a widespread and accepted species of the Brassicaceae family, native to Northern Africa, Asia and Southern Europe (USDA-ARS, 2015). Brassica is a large genus with The Plant List (2013) recording 384 plant names, 39 of which are accepted species names (The Plant List, 2013).

It is commonly referred to as African mustard or Sahara mustard. The Plant List (2013) has 16 recorded synonyms, including a number of varieties.

Description

B. tournefortii is an erect annual herb that has stems that can be from 10 to 100 cm tall, and a well-developed sturdy taproot system. It has a good number of primary stems and a large number of secondary stems that can be as high as 40. The size of the herb can vary considerably depending on soil moisture (Pratap and Gupta, 2009). The lower stems are densely covered with stiff bristles (Graham et al., 2005).

The leaves are green and usually moderately well-developed basal rosette. The lower leaves are large and reduce in size upwards along the stem. During inflorescence only minute bracts are present at the top of the herbs stem (Minnich and Sanders, 2000). The leaves vary from 7-30 cm in length and are pinnately lobed, 8-14 lobes per leaf. The leaves are further toothed with serrate-dentate margins (Pratap and Gupta, 2009).

During inflorescence a typical stem will consist of racemes of 6 to 20 flowers. The racemes become greatly elongated when in fruit. The flowers are a dull yellow in colour and are inconspicuous. Individual flowers are approximately 1.5 cm in width with the petals measuring between 5-7 mm in length. The sepals measure 3 mm in length. The pedicels, when the herb is in flower measure between 4-10 mm, when in fruit the pedicel are elongated to between 10-20 mm in length. The pedicels diverge from the stem at about a 45 degree angle.

The fruit of B. tournefortii is dehiscent silique, typical of fruit of the mustard family, and is about 3.5-6.5 cm long with a diameter of 2-3 mm. The fruit consists of 2 locules. Each locule contains a single row of 7-15 seeds. The fruit ends with an obvious terete beak capsule, 1-2 cm long. The seeds are red and have a globose form with a diameter of 1mm (Minnich and Sanders, 2000). 

Plant Type

Distribution

B. tournefortii is a widespread mustard native to Africa, Asia and Europe. The species has become widely spread and naturalised in North America, Australia and New Zealand (USDA-ARS, 2015).

Specifically, B. tournefortii occurs in the Northern African countries of Algeria, Libya, Egypt, Tunisia and Morocco. It is widely spread across the Middle East and Western and Central Asia, including Oman, Saudi Arabia, Azerbaijan, Uzbekistan, Iraq, Syria and Turkey . It is also native to the European countries of Italy, Greece and Spain (USDA-ARS, 2015).

B. tournefortii has become naturalised in South Africa, Australasia (Australia and New Zealand), the UK, Mexico and the southern parts of the USA (USDA-ARS, 2015).

It has recently been recorded as a new alien species in Chile (Tellier et al., 2014).

Distribution Table

The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

History of Introduction and Spread

In the USA, a sample of B. tournefortii was first collected in 1927 in the Coachella Valley, California. It is believed that the species was accidently introduced with the importation of date palms from the Middle East. This is probable due to the development of the date industry in the Coachella Valley in the early part of the twentieth century (Minnich and Sanders, 2000).

There is little information regarding the introduction of B. tournefortii to other countries. In Australia the earliest recorded sample of the species by AVH (2015) is dated 23 March 1936.

Introductions

Risk of Introduction

B. tournefortii is a highly invasive species thus its spread and further introduction is of high concern. Curtis and Bradley (2015) modelled the current and future climatic suitability for establishment of B. tournefortii in the southwestern USA, concluding that the species presence and abundance may increase by 29% and 28% respectively.

Following spatial analysis and climatic modelling of B. tournefortii,Li et al. (2015) found that that the climate in the invaded range generally predicts the native distribution. 

Habitat

B. tournefortii is commonly found in disturbed sites along roadsides, abandoned fields and waste grounds. Its native habitat is typically areas of wind blown, sandy arid, or semi-arid environments (Minnich and Sanders, 2000). It also inhabits sandy coastlines typically along the Mediterranean coastline (Thanos et al., 1991). During years of high rainfall it also has been found to inhabit areas of silty and rocky soils (Cal-IPC, 2015).

Berry et al. (2014) found that in the western Sonoran Desert of California, USA, B. tournefortii quickly invaded areas of natural disturbance where soils were young while older geological surfaces were less vulnerable to invasion. Another study in central-western New South Wales, Australia, found that rabbit mounds enhanced the germination of B. tournefortii seeds. The mounds were characterised as disturbed and degraded soil surfaces, suggesting that an increased abundance of B. tournefortii in the area can be attributed to the soil disturbance caused by rabbits (Eldridge and Simpson, 2002).

Habitat List

Hosts/Species Affected

Australian Oilseeds Federation (2015) reported that B. tournefortii can contaminate canola oil crops, reducing yield through competition, and compromising oil quality. 

Host Plants and Other Plants Affected

Growth Stages

Biology and Ecology

Genetics

The chromosome count for B. tournefortii was reported to be 2n=20 (Jepson Flora Project, 2014).

B. tournefortii has been hybridized with cultivated Brassica napus (rapeseed) to establish cytoplasmic male sterility B. napus (Liu et al., 1996). Phoma Lingam (black leg disease of Brassica crops) resistance has been shown to be transferred from B. tournefortii to the hybrid plants (Liu et al., 1995). In addition, due to B. tournefortii’s drought resistant genes it has been identified as a possible donor for hybridization with cultivated brassicas (Pratap and Gupta, 2009).

Reproductive Biology

B. tournefortii is an autogamous species with virtually one hundred percent fruit set. A well-developed plant will produce between 750 and 9000 seeds (Minnich and Sanders, 2000). Seeds may remain viable for up to three years (USDA, 2015). It has been reported that the seeds of B. tournefortii can also remain viable after extended submergence (Bangle et al., 2008).

In the Mediterranean region it is reported that seed germination is optimal between 15-25°C (Thanos et al., 1991), compared with 16-35°C in southwest USA (Bangle et al., 2008). Germination is light sensitive, and can be inhibited when exposed to light (Thanos et al., 1991). Malusa et al. (2003) found that seeds lying on the surface did not germinate due to photo-inhibition.

The gel like coating on the seeds waterproofs them and makes them sticky when wet. This enables the seed to survive and remain dormant for a number of months (Holman and Gardener, 2006).

Physiology and Phenology

B. tournefortii is a rapid growing annual, which germinates in the autumn, flowers and fruits in the winter and senesces in the spring. In California, seed germination occurs as a response to rains as small as 4 cm, the plant then grows vigorously within two or three months. The fast growth enables early establishment. In the Sonoran Desert it has been reported that the abundance of B. tournefortii increases with higher winter rainfall. It has been noted that hot dry spells cause B. tournefortii to prematurely flower and fruit (Minnich and Sanders, 2000).

Minnich and Sanders (2000) state that the plant population size can vary from year to year. In the Sonoran Desert it has been reported that population abundance is higher in winters of high rainfall compared with winters of low rainfall (Minnich and Sanders, 2000).

Associations

Sanchez-Flores et al. (2008) report that B. tournefortii shows association with microphyllous desert scrub, grassland, and sarcocaulescent desert scrub through land cover characterization.    

Environmental Requirements

B. tournefortii is suited to arid and semi-arid sandy desert conditions; however, it inhabits a wide variety of disturbed environments (USDA, 2015). Minnich and Sanders (2000) found that it is becoming more common in the semi-arid coastal areas of California. They noted that it is particularly common in areas of wind blown sediments.

B. tournefortii favours sandy disturbed soils, and can tolerate soil salinity (ASDM, 2015). It requires very low soil nutrient levels, and is able to grow in extremely poor soils and sand dunes (Dremann, 2005). Plants for a Future (2015) report that B. tournefortii prefers well-drained yet moist soils and that it cannot grow in the shade. It can be found at elevations as high as 1000 m though is abundant below 305 m (Minnich and Sanders, 2000). Malusa et al. (2003) found that B. tournefortii in the Mohawk dunes, Arizona, preferred areas of greatest moisture. In the Coachella Valley, California, B. tournefortii favours years of higher precipitation, biomass abundance drops in years of low precipitation (Barrows et al., 2009).

Following spatial analysis and climatic modelling of B. tournefortii,Li et al. (2015) found that that the climate in the invaded range generally predicts the native distribution. Therefore, suggesting that either there has been little local adaptation to climate occurring since introduction or the biological interaction experienced in the invaded range has not driven the species to occupy climatic conditions much different from its native range.

Climate

Latitude/Altitude Ranges

Air Temperature

Rainfall

Rainfall Regime

Soil Tolerances

Soil drainage

• free

Soil reaction

• acid
• alkaline
• neutral
• very alkaline

Soil texture

• heavy
• light
• medium

Special soil tolerances

• infertile
• saline
• shallow
• sodic

Natural enemies

Notes on Natural Enemies

There is little information on natural enemies of B. tournefortii. Suazo et al. (2012) concluded that harvester ants in the Mojave Desert, Arizona, might act as seed predators. Harvester ants carried B. tournefortii seeds to their nests and as plant density was lower near the ant’s nest it was concluded that the ants were seed predators rather than seed dispersers (Suazo et al., 2012). 

Means of Movement and Dispersal

B. tournefortii spreads exclusively via seed dispersal. The main methods of dispersal include both natural transmission and vector dispersal (USDA, 2015).

Natural Dispersal

B. tournefortii seeds have been reported to be dispersed by both wind and water (USDA, 2015). Evidence shows that seeds can be dispersed by the tumbleweed effect. When the plant dies and dries out it can easily break off and tumble in the wind across the landscape spreading the dried seeds to new locations (USDA, 2015).

It has also been observed that B. tournefortii seeds can remain viable when submerged for long periods, thus can float across bodies of water (Bangle et al., 2008). Powell (2005) found seeds that had been underwater in Lake Mead, Arizona, for 11 weeks remained viable and germinated.

Vector Transmission

B. tournefortii seeds are known to be carried and dispersed by animals. When seeds become wet a sticky gel forms. This enables the seed to adhere to passing animals and be carried long distances (Minnich and Sanders, 2000). Furthermore, USDA (2015) reports that rodents cache and move the seeds far from their original source. Powell (2005) observed in Lake Mead National Recreation Area, Arizona, that rodents carried seeds into the open desert to their burrows, some distance from the original B. tournefortii infestation. San (2010) reported that as well as rodents, ants are a potential seed disperser in the Lake Mead area.

Accidental Introduction

B. tournefortii was first recorded in the USA in 1927 in the Coachella Valley, California. It is believed to have been accidently introduced when date palms were imported from the Middle East in the early part of the twentieth century (Minnich and Sanders, 2000). B. tournefortii is now abundant across parts of California and Arizona (USDA, 2015). The movement and seed dispersion has occurred along roadsides when seeds adhere to vehicles and road maintenance equipment (Minnich and Sanders, 2000). Consequently seeds have been dispersed over long distances.

Pathway Causes

Pathway Vectors

Impact Summary

Economic Impact

The Australian Oilseeds Federation (2015) reported that B. tournefortii can reduce canola yield through competition. In addition the similar seed size can result in crop contamination and impact the oil quality.

Environmental Impact

Impact on Habitat

B. tournefortii biomass increases the fuel load for wildfires (Minnich and Sanders, 2000), creating a fire hazard in an ecosystem previously unaffected by fire and where native species are not adapted to survive fire (Barrows, 2010).

Impact on Biodiversity

In southwestern USA a rapid invasion of B. tournefortii has been observed to be having negative consequences for native wildflowers. B. tournefortii is fast growing and its early phenology makes it a highly invasive species that results in the suppression of native wildflowers, shifting the composition of desert flora (Minnich and Sanders, 2000; Barrow et al. 2009). Holt and Barrows (2014) observed that in areas of dense B. tournefortii growth, native annuals grew taller in order to compete for light under the canopy of B. tournefortii. Consequently the native plants produced fewer flowers and seeds due to the plants energy being focused on height growth. This resulted in a 90% reduction in the reproductive success of the native flora and subsequently leading to a depleted seed bank of the native wildflowers.

Its suppression of natives results in B. tournefortii being the dominant species in areas of usually diverse flora. In 2005 it was approximated that three quarters of wildflower areas in California and Arizona were invaded by B. tournefortii (ASDM, 2015). B. tournefortii has a similar affect on native herbaceous plants in Australia (Weeds of Australia, 2015).

There is little information regarding the impact of B. tournefortii on fauna. It has been reported that the high oxalic acid content of B. tournefortii may be toxic to the desert tortoise (Gopherus spp.) and other desert herbivores (Holman and Gardener, 2006). Barrows et al. (2009) have noted the Coachella Valley fringe-toed lizard (Uma spp.) had a negative response to the abundance of B. tournefortii. 

Threatened Species

Social Impact

B. tournefortii leaves and young shoots are edible and its seeds can be used to obtain oil (PFAF, 2015). In India and Tibet, B. tournefortii is cultivated on a small scale as an oil crop (Hammer et al., 2013).

Risk and Impact Factors

• Proved invasive outside its native range
• Has a broad native range
• Abundant in its native range
• Highly adaptable to different environments
• Is a habitat generalist
• Pioneering in disturbed areas
• Highly mobile locally
• Fast growing
• Has high reproductive potential
• Has propagules that can remain viable for more than one year
• Reproduces asexually
• Has high genetic variability

• Ecosystem change/ habitat alteration
• Modification of fire regime
• Monoculture formation
• Negatively impacts agriculture
• Negatively impacts animal health
• Reduced amenity values
• Reduced native biodiversity
• Threat to/ loss of native species

• Competition - monopolizing resources
• Competition - shading
• Competition - smothering

• Highly likely to be transported internationally accidentally
• Difficult to identify/detect as a commodity contaminant
• Difficult/costly to control

Uses

B. tournefortii is not widely cultivated for use. However, it is used as a small-scale oil crop in north west India and western Tibet (Hammer et al., 2013).

Uses List

Human food and beverage

• Oil/fat
• Vegetable

Similarities to Other Species/Conditions

B. tournefortii can be confused with other yellow flowering mustards in the field, including Hirschfeldia icana (shortpod mustard), Brassica nigra (black mustard), B. juncea (Indian mustard) and B. napus (rapeseed) (BCC, 2015). B. tournefortii can be distinguished from other yellow flowering mustards by its pale, dull in comparison, small yellow flowers and the stiff white bristles on the herbs lower stems. Also the fruit of B. tournefortii is relatively elongated with a long beak (Di Tomaso and Healy, 2007).

In the USA, the Sahara Mustard and Volutaria Eradication Task Force (2015) have noted a few native desert plants that co-occur and are similar in appearance to B. tournefortii. These include Descurainiapinnata (tansy mustard), Guillenia lasiophylla (California mustard) and Camissonia californica (false mustard). Identification and differentiation is important for the control and eradication of B. tournefortii in these native habitats.

Prevention and Control

B. tournefortii can not be effectively controlled in one year. Multiple management methods need to be applied over multiple years in order to effectively control a B. tournefortii invasion. Effectiveness of control increases by using a combination of methods (USDA, 2015).

A study on seed production by Trader et al. (2006) found that seed production of individual plants can be higher in plots with lower densities. Therefore, control measures that reduce density but do not clear the entire area of plants may result in an increase in net seed production from those individuals that have not been removed.   

Cultural Control and Sanitary Measures                      

Early detection and removal is vital to inhibiting the spread of B. tournefortii. Education and public awareness regarding B. tournefortii’s invasiveness, and identification at different life stages, will lead to the public aiding prevention and control by reporting new infestations. In addition land users should be discouraged to use vehicles and machinery, and graze livestock in infested areas in order to mitigate the spread of seeds (USDA, 2015).

Physical/Mechanical Control

Hand weeding is the most common method of control (Holt and Barrows, 2014). However it is only effective where an infestation has been detected in the early stages, it is not a feasible option for large scale infestations of B. tournefortii (Barrows, 2010). The entire plant should be removed, bagged and disposed of off site (USDA, 2015). Abella et al. (2013) showed that physical treatment worked best in the early stages of B. tournefortii growth and seed development.

Biological Control

The use of biological control may not be suitable due to B. tournefortii being closely genetically related to a number of important agricultural crops such as broccoli (Brassica oleracea), canola (Brassica spp.) and cabbage (Brassica oleracea). Finding a bio-control that would not attack the cultivated species may be difficult (Holt and Barrows, 2014).

Chemical Control

Chemical control, such as herbicides, are an effective control against B. tournefortii. Unlike physical control it can be effective once the plant has reached the seed developmental stages of its lifecycle (Abella et al., 2013). Herbicide treatment when used in ecosystems such as Mojave Desert or Coachella Valley may cause a negative impact on the surrounding native wildflowers. However, the early phenology of B. tournefortii provides a window for selective control using herbicides without affecting the native annual wildflowers. Early treatment of B. tournefortii would reduce its abundance and allow native wildflowers to germinate and establish (Holt and Barrows, 2014). Chemical control may be best suited when B. tournefortii infests agricultural crops.

Monitoring and Surveillance

Recent studies, e.g. Sankey et al. (2014), have used high spatial resolution to detect presence, cover and biomass of B. tournefortii.

References

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Contributors

27/01/2016 Original text by:

Madeleine Florin, Consultant, UK 

Distribution Maps