Sisymbrium irio

Pictures

Picture	Title	Caption	Copyright
Title Flowering habit Caption Sisymbrium irio (London rocket); upright flowering habit. East Geelong saltworks, Australia. September, 2004. Copyright ©Robert G. & Fiona J. Richardson - 2004. All Rights Reserved.	Flowering habit	Sisymbrium irio (London rocket); upright flowering habit. East Geelong saltworks, Australia. September, 2004.	©Robert G. & Fiona J. Richardson - 2004. All Rights Reserved.
Title Habit in shallow water Caption Sisymbrium irio (London rocket); habit in shallow water. East Geelong saltworks, Australia. October, 2004. Copyright ©Robert G. & Fiona J. Richardson - 2004. All Rights Reserved.	Habit in shallow water	Sisymbrium irio (London rocket); habit in shallow water. East Geelong saltworks, Australia. October, 2004.	©Robert G. & Fiona J. Richardson - 2004. All Rights Reserved.
Title Inflorescence Caption Sisymbrium irio (London rocket); leaves, showing bronzing. East Geelong saltworks, Australia. Copyright ©Robert G. & Fiona J. Richardson - 2005. All Rights Reserved.	Inflorescence	Sisymbrium irio (London rocket); leaves, showing bronzing. East Geelong saltworks, Australia.	©Robert G. & Fiona J. Richardson - 2005. All Rights Reserved.
Title Fruit capsules Caption Sisymbrium irio (London rocket); fruit capsules. East Geelong saltworks, Australia. October, 2004. Copyright ©Robert G. & Fiona J. Richardson - 2004. All Rights Reserved.	Fruit capsules	Sisymbrium irio (London rocket); fruit capsules. East Geelong saltworks, Australia. October, 2004.	©Robert G. & Fiona J. Richardson - 2004. All Rights Reserved.

Identity

Preferred Scientific Name

• Sisymbrium irio L.

Other Scientific Names

• Norta irio (L.) Britton

Local Common Names

• : desert mustard; rocket mustard
• : ireos; matacandil; oruga leonina; rabanillo amarillo
• Denmark: Esdragon
• Sweden: Ampelskara; Dragon; vallsenap

Summary of Invasiveness

S. irio is an annual or winter-annual, herbaceous, stiffly erect, tap-rooted plant. It first came to prominence as an invasive species, and gained its common name ‘London rocket’ when it became abundant after the Great Fire of London in 1666.

The well-known yellow flowered weed is native to southern Europe, North Africa and temperate Asia but has been carried by migrants to North America, Australasia and South Africa. In North America, S. irio is naturalised in south-western States and in Mexico, where it is often abundant, like elsewhere, in abandoned fields and other neglected areas, as well as in pastures, livestock watering sites, and open deserts. In Australia, it is described as a widespread weed of crops, pastures, roadsides, parks, gardens, lawns, footpaths, disturbed sites and waste areas. It is classed as invasive in Hawaii (PIER, 2014).

The plants produce a large number of seeds which can be introduced to countries accidentally as a contaminant in crop seed or deliberately by migrants.

Taxonomic Tree

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

Notes on Taxonomy and Nomenclature

Sisymbrium irio is one of about 90 species of the genus whose members are found across Eurasia, the Mediterranean, southern Africa, North America and the Andes (Mabberley, 1997). The most common invasive species of the genus are S. irio itself, S. altissimum, S. officinale and S. orientale, all of which have been introduced to and become naturalised in many countries.

It first came to prominence as an invasive species, and gained its common name ‘London rocket’ when it became abundant after the Great Fire of London in 1666 (Clapham et al., 1952)

Description

The following description is adapted from Flora of North America (2013).

Annual or biennial; glabrous or sparsely pubescent. Stems erect, branched proximally and distally, (1-)2-6(-7.5) dm, glabrous or sparsely pubescent at least basally. Basal leaves not rosulate; petiole (0.5-)1-4.5(-6) cm; blade oblanceolate or oblong (in outline), (1.5-)3-12 (-15) cm × (5-)10-60(-90) mm, margins runcinate to pinnatisect; lobes (1-)2-6(-8) on each side, oblong or lanceolate, smaller than terminal lobe, margins entire, dentate, or lobed. Cauline leaves similar to basal; distal-most blade smaller, to 2 cm wide, margins entire or 1-3-lobed. Fruiting pedicels divaricate or ascending, slender, much narrower than fruit, (5-)7-12(-20) mm. Flowers: sepals erect, oblong, 2-2.5 × 1-1.5 mm; petals oblong-oblanceolate, 2.5-3.5(-4) × 1-1.5 mm, claw 1-1.5 mm; filaments 2.5-4 mm; anthers ovate, 0.5-0.9 mm. Fruits (divaricate to ascending, young fruits overtopping flowers), narrowly linear, straight or slightly curved inward, slightly torulose, slender, (2.5-)3-4(-5) cm × 0.9-1.1 mm; valves glabrous; ovules 40-90 per ovary; style 0.2-0.5 mm; stigma prominently 2-lobed. Seeds 0.8-1 × 0.5-0.6 mm.

Maximum height of the plant can range from 50-80 cm or taller. 

Plant Type

Distribution

S. irio is native to southern Europe, North Africa and temperate Asia but has been carried by migrants to North America, Australasia and South Africa, where it has naturalised and become a well-known, yellow-flowered weed of waste and neglected areas. Its transport to the far corners of the globe has either been by accidental movement of seeds (sometimes as a contaminant of crop seeds, agricultural produce, etc.) or by deliberate transport of seeds since the plant has been used for herbal medicines and food. 

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

S. irio seems to have appeared in both North America and Australia in the early 1900s, but how it reached either place remains unknown (Robbins, 1940; Wilken and Hannah 1998; Council of Heads of Australasian Herbaria, 2013). Possible pathways include its deliberate introduction as a herb, or accidental introduction as a contaminant of crop seed. 

Introductions

Risk of Introduction

The risk of introduction to the few countries where S. irio is neither native nor naturalised is quite high, either as seed deliberately taken there by migrants or accidentally as a contaminant in crop seed. Modern phytosanitary precautions ought to prevent such occurrences but regulations are not strongly enforced in all countries. 

Habitat

In its native environment S. irio can be found in abandoned fields, waste places, roadsides and orchards. According to Wilken and Hannah (1998), it can be found in much the same disturbed habitats where it has become naturalised. In North America, for example, where it is found in western States and Mexico, it occurs in abandoned fields, waste places, vacant lots, off-highway vehicle staging areas, orchards, pastures, livestock watering sites, roadsides and open deserts (Parker 1972, Rollins, 1993; Wilken and Hannah, 1998; DeFalco and Brooks, 1999; Guertin, 2003). It tends to grow best where its seeds can germinate undisturbed by shade or vegetation and where plants can grow with limited competition.

In Australia, where it is widely naturalised in southern, central and eastern Australia, it inhabits pastures, roadsides, parks, gardens, lawns, footpaths, disturbed sites and waste areas and is also a widespread weed of crops (Weeds of Australia, 2013).

Habitat List

Hosts/Species Affected

Marshall et al. (2000) report that invasion by S. irio competes with or displaces native annual plant species (in North America and possibly elsewhere).

Biology and Ecology

Genetics

2n = 14, 28, 42, 56 (Khooshoo, 1955; Guertin, 2003), although Flora of North America (2013) states 2n=14. Khooshoo (1955) reported from India that: ‘S. irio Linn. is a polytypic winter annual which grows throughout the Panjab plains. It occurs in diploid, triploid, tetraploid, hexaploid and octoploid races. All these races can be considerably modified in response to varying amounts of moisture and sunlight.’

Reproductive Biology

The tap-rooted herbaceous plant reproduces entirely by seed. Wilken and Hannah (1998) suggest that S. irio, like other colonising mustards, is self-compatible and self-pollinated, as suggested by its small flowers. It has been estimated that a large plant can produce 9500 seeds or more (Guertin, 2003). Seeds are dispersed when the fruit splits, dropping the seeds to the ground beneath the parent plant.

Physiology and Phenology

In Australia, the seed germinates from autumn to winter and the plant grows without forming a rosette, branching freely from the base to form a bushy appearance. The flowers appear from the tops of the stems in late winter to early spring. As the fruits mature the stem elongates and new flowers are added to the cluster at the top (Herbiguide, 2013).

In California, Guertin (2003) reports that the seeds of S. irio germinate from October to March (autumn through to spring) and the plants mature from April to May. In contrast in Arizona, plants flower from December to May but in moist cultivated fields they can flower all summer (Parker, 1972; Guertin, 2003): usually plants disappear as temperatures rise.

In Pakistan, this species is known to flower between March and May (Flora of Pakistan, 2013).

Ray et al. (2005) studied the factors affecting the emergence of S. irio, one of the very few studies on its germination. They determined that 100 seeds weighed 8.5 mg ± 0.05 SE. Germination was tested at 5 ^oC, 15 ^oC and 25^oC and found to be best at 15^oC, although some seeds germinated at the other temperatures. When seeds were buried at different depths in the soil, emergence was greatest (almost 50%) for seed buried at 2 mm, followed by depths of 1 mm and 3 mm. The same authors tested the interactions between temperature and soil moisture requirements for germination and found that seeds emerged between temperatures of 5^oC and 30^oC but that maximum emergence was predicted to take place at soil moisture tensions of – 0.01 to 11.2MPa and between 15^oC and 20^oC. The authors suggested that their data could be useful in developing models of S. irio emergence and thus a predictive model of beet curly top virus occurrences; since the sporadic nature of the outbreaks of the virus in New Mexico may be related to the timing of S. irio emergence.

Although relatively little information seems to be available on the germination of S. irio, more is known about the germination of the closely related S. officinale, and this may give a guide to that of S. irio. In S. officinale both light and nitrate are needed for germination, with the nitrate supplied exogenously or present endogenously in the seed (Hilhorst and Karssen, 1988). Bouwmeester and Karssen (1993) found that buried seeds of S. officinale showed seasonal changes in dormancy, with dormancy being reduced in periods of low temperature and induced in periods of high temperature, with temperature apparently the only factor influencing these changes. However, light, nitrate or desiccation all stimulated germination of exhumed seeds. The roles of light and nitrate in the germination and dormancy of S. officinale seeds was also examined by Hillhorst (1990a; 1990b).

Longevity

The plant itself is an annual or winter annual without any means of vegetative reproduction. The seeds seem to be able to survive in low numbers in the seed bank. Gomaa (2012) found vegetative plants growing on reclaimed land in the Eastern Desert of Egypt and also recovered 7.3 seeds m^-2 from the top 5 cm of the soil. DiTomaso et al. (2013), report that the seeds can survive for up to about 10 years in the soil.

Associations

Like most plants inhabiting waste spaces, cultivated land, pastures and roadsides, S. irio is found growing in association with many other species. Such associations vary widely between countries and also between individual habitats.

Environmental Requirements

S. irio seems to be capable of growing under a wide range of conditions, provided that its seeds can germinate in full sun and without the hindrance of overlying vegetation.

Climate

Notes on Natural Enemies

Ray et al. (2005) reported that S. irio can be a primary overwintering host of the beet leafhopper (Circulifer tenellus) and of the beet curly top virus in southern New Mexico.

S. irio is capable of sustaining populations of the tarnished plant bug Lygus lineolaris, an increasingly important cotton pest, especially during the late season overwintering period of the pest (Esquivel and Mowery, 2007).

DiTomaso et al. (2013) noted that like other mustards S. irio can harbour (and be affected by) diseases and pests that attack related species in the same Brassicaceae family. 

Means of Movement and Dispersal

Natural Dispersal

At maturity, Guertin (2003) reports that the stem of S. irio can break off at ground level causing the plant to be blown by the wind, scattering its seeds. However, DiTomaso et al. (2013) imply that this only occurs with the related species S. altissimum (commonly called ‘tumbleweed’) and not with S. irio.

Vector Transmission

Drezner et al. (2001) reported that S. irio is dispersed primarily by birds and mammals.

Accidental Introduction

Seeds of S. irio may be transported as a contaminant of crop seeds, wool or grain. For example, in Belgium the species is rare but increasing and has been found as a ‘wool alien’ (a contaminant of wool imported for processing), a ‘grain alien’ (contaminating imported grain) and also as a weed in containers with olive trees from southern Europe (Hoste and Verloove, 2009; Manual of the Alien Plants of Belgium, 2013). The species is also mentioned as a wool alien in Britain (Salisbury, 1964).

Modern phytosanitary precautions ought to reduce these sources of imported seeds, but are unlikely to prevent them altogether.

Intentional Introduction

Deliberate carriage of seeds or plant material across international land borders is a possibility as parts of the plants may be used for food or as medicinal herbs. 

Pathway Causes

Pathway Vectors

Impact Summary

Economic Impact

S. irio appears to be mostly a weed of disturbed, open habitats and there it is one of a raft of weedy species occurring along roadsides, in parks and gardens, and in waste places. However, it does occur as a pasture weed in Australia, and at least one report implicates it in the poisoning of cattle there (McKenzie et al., 2009). In light of that, Al-Mujalli et al. (2013) investigated the effects of the species on goats in areas of Saudi Arabia where this species grows, and where camels, sheep and goats are raised. They concluded that feeding on S. irio could result in ‘some derangement in blood cells and biochemical constituents’ and the authors detected slight disturbances in the physical activities of the goats, but considered that further tests were needed to investigate the effects.

Ray et al. (2005) expressed concerns that S. irio may be a primary overwintering host of the beet leafhopper (Circulifer tenellus) in southern New Mexico, as well as of the beet curly top virus which the leafhopper transmits to Chile pepper (Capsicum annuum) crops. It can also host the tarnished plant bug (Lygus lineolaris), a cotton pest, in cotton-growing areas of the southern United States.

Environmental Impact

Impact on Habitats

Cal-IPC (2013) suggests that S. irio may impact on fire regimes in North America by increasing fuel loads, but adds that this is only likely to occur where alien grass species have already altered the fire regime so its additional contribution will be only slight. S. irio plants produce large amounts of biomass early in the season and so may usurp soil water before native North American species reach peak development (Cal-IPC, 2013).

Impact on Biodiversity

DiTomaso et al. (2013) noted that S. irio can replace native annuals in wildland settings in California.

Cal-IPC (2013) considers it possible that the desert tortoise (Gopherus agasizii), native to the Mojave desert and Sonoran desert of the southwestern United States and northwestern Mexico and the Sinaloan thornscrub of northwestern Mexico, may suffer negative physiological effects from consuming S. irio, but this is at present only conjecture.

Risk and Impact Factors

• Proved invasive outside its native range
• Has a broad native range
• Pioneering in disturbed areas
• Fast growing
• Has high reproductive potential

• Competition - monopolizing resources

• Difficult to identify/detect as a commodity contaminant

Uses

Economic Value

Al-Qudah and Abu Zarga (2010) examined the chemical constituents of S. irio growing in Jordan and found it to be a rich source of flavonoids and glucosinates, but whether any of these have any commercial value is yet to be tested.

Social Benefit

According to Bailey and Danin (1981) the stems, leaves and flowers of S. irio are used as food by the Bedouin in Sinai and the Negev, and the leaves (presumably) are used as a tobacco substitute. Chopra et al. (1956) found that the seeds are expectorant, restorative and a stimulant. They are used for the treatment of asthma, and can be used as a stimulating poultice. An infusion of the leaves is used in treating affections of the throat and chest. 

Uses List

Medicinal, pharmaceutical

• Traditional/folklore

Similarities to Other Species/Conditions

S. irio is similar to other species of Sisymbrium such as S. officinale and S. orientale, but both species differ from S. irio in having the fruiting pedicels (the stalk below each individual fruit capsule) about the same width as the fruit capsule and a denser pubescence on the stems and leaves (Wilken and Hannah, 1998). S. officinale has short, appressed fruiting pedicels and beaked fruits that are 8-20 mm long, whilst S. orientale has a basal rosette of leaves, pubescent ovaries and young fruits and mature fruits that are 35-100 mm long. 

Prevention and Control

Physical/Mechanical Control

Herbiguide (2013) recommends removing isolated plants (presumably before they set seed and thus multiply). DiTomaso et al. (2013) say that hand pulling is a viable control method if the population is small and isolated, but is time-consuming and is not recommended for large or widespread infestations. Cultivation is effective provided it is done before seed production. Apparently solarisation can be effective in areas with hot summers.

Biological Control

DiTomaso et al. (2013) say that no microbial pathogens or insect biocontrol agents are available for the control of S. irio.

Chemical Control

Herbiguide (2013) recommends the use of diflufenican for controlling S. irio, and this can be used selectively in lupins, clovers and some other crops. Glyphosate gives effective control and can to some extent reduce seed production but also kills all other vegetation it touches.

DiTomaso et al. (2013) suggest a range of herbicides for control of S. irio, some of which are selective to grasses whilst others will kill all green vegetation. Herbicides that can be used include 2,4-D, aminocyclopyrachlor + chlorsufuron, aminopyralid + metsulfuron, dicamba, glyphosate, chlorsulfuron, metsulfuron-mehtyl, sulfometuron, imazapic, imazapyr, propoxycarbazone-sodium, rimsulfuron, sulfosulfuron, and hexazinone. As with the use of any weed-killer, it is important to read the package carefully before starting any weed control operation as some require special precautions to be taken.

Control by Utilization

Grazing is an effective control method if it is early enough to prevent seed production. DiTomaso et al. (2013) recommend using sheep rather than cattle because sheep graze closer to the ground. They also point out that meat and milk can be tainted if cattle graze large quantities of mustard-type plants. 

Gaps in Knowledge/Research Needs

Little published information surrounds seed germination, seed longevity and growth rates of the seedlings or the plants. Further studies on its impacts on crops or associated species are also needed. 

References

Alien plants of Belgium, 2013. Manual of the alien plants of Belgium. National Botanic Garden of Belgium. from http://alienplantsbelgium.be/

Al-Mujalli AM; Fouda TA; Hussein HA, 2013. Effects of London rocket (Sisymbrium irio) on goats' health: clinical and laboratory studies. Bulgarian Journal of Veterinary Medicine, 16(1):48-52. http://tru.uni-sz.bg/bjvm/BJVM-March%202013%20p.48-52.pdf

Al-Qudah MA; Abu Zarga MH, 2010. Chemical constituents of Sisymbrium irio L. from Jordan. Natural Products Research, 24(5):448-56.

Bailey C; Danin A, 1981. Bedouin plant utilization in Sinai and the Negev. Economic Botany, 35(2):145-162.

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Wilken D; Hannah L, 1998. Sisymbrium irio (Brassicaceae) London Rocket. Santa Barbara Botanic Garden, for Channel Islands National Park. Sisymbrium irio (Brassicaceae) London Rocket. California, USA: Santa Barbara Botanic Garden, Channel Islands National Park, 4 pp. http://sbsc.wr.usgs.gov/research/projects/swepic/factsheets/Sisymbrium_spp.pdf

Contributors

17/11/2013 Original text by:

Ian Popay, consultant, New Zealand, with the support of Landcare Research

Distribution Maps