Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Datasheet

Solanum mauritianum
(tobacco tree)

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Datasheet

Solanum mauritianum (tobacco tree)

Summary

  • Last modified
  • 08 November 2018
  • Datasheet Type(s)
  • Invasive Species
  • Pest
  • Host Plant
  • Preferred Scientific Name
  • Solanum mauritianum
  • Preferred Common Name
  • tobacco tree
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Dicotyledonae
  • Summary of Invasiveness
  • The South American tree S. mauritianum has been introduced to Africa, Australasia, India and islands of the Atlantic, Indian and Pacific Oceans. Worldwide, the worst infestations occur in the high rainfall regions of South Africa, where the weed inva...

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Pictures

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PictureTitleCaptionCopyright
S. mauritianum flowers and fruits, prolifically in its introduced range.
TitleFoliage and flowers
CaptionS. mauritianum flowers and fruits, prolifically in its introduced range.
CopyrightR.P. Denny/ARC-PPRI
S. mauritianum flowers and fruits, prolifically in its introduced range.
Foliage and flowersS. mauritianum flowers and fruits, prolifically in its introduced range.R.P. Denny/ARC-PPRI
Ripe fruit of S. mauritianum are favoured by frugivorous birds.
TitleRipe fruits
CaptionRipe fruit of S. mauritianum are favoured by frugivorous birds.
CopyrightP.L. Cambell/ARC-PPRI
Ripe fruit of S. mauritianum are favoured by frugivorous birds.
Ripe fruitsRipe fruit of S. mauritianum are favoured by frugivorous birds.P.L. Cambell/ARC-PPRI
S. mauritianum invading cleared areas in forestry plantations in South Africa.
TitleHabit
CaptionS. mauritianum invading cleared areas in forestry plantations in South Africa.
CopyrightR.P. Denny/ARC-PPRI
S. mauritianum invading cleared areas in forestry plantations in South Africa.
HabitS. mauritianum invading cleared areas in forestry plantations in South Africa.R.P. Denny/ARC-PPRI
The leaf-sucking Gargaphia decoris, a biocontrol agent established in South Africa.
TitleNatural enemy
CaptionThe leaf-sucking Gargaphia decoris, a biocontrol agent established in South Africa.
CopyrightT. Olckers/ARC-PPRI
The leaf-sucking Gargaphia decoris, a biocontrol agent established in South Africa.
Natural enemyThe leaf-sucking Gargaphia decoris, a biocontrol agent established in South Africa.T. Olckers/ARC-PPRI
Extensive leaf chlorosis caused by high population densities of Gargaphia decoris.
TitleNatural enemy damage
CaptionExtensive leaf chlorosis caused by high population densities of Gargaphia decoris.
CopyrightT. Olckers/ARC-PPRI
Extensive leaf chlorosis caused by high population densities of Gargaphia decoris.
Natural enemy damageExtensive leaf chlorosis caused by high population densities of Gargaphia decoris.T. Olckers/ARC-PPRI
Anthonomus santacruzi, a flowerbud weevil proposed for release in South Africa.
TitleNatural enemy
CaptionAnthonomus santacruzi, a flowerbud weevil proposed for release in South Africa.
CopyrightT. Olckers/ARC-PPRI
Anthonomus santacruzi, a flowerbud weevil proposed for release in South Africa.
Natural enemyAnthonomus santacruzi, a flowerbud weevil proposed for release in South Africa.T. Olckers/ARC-PPRI

Identity

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Preferred Scientific Name

  • Solanum mauritianum Scop.

Preferred Common Name

  • tobacco tree

Other Scientific Names

  • Solanum auriculatum Ait.
  • Solanum carterianum Rock.
  • Solanum erianthum D. Don.
  • Solanum tabacifolium Vell.
  • Solanum verbascifolium var. auriculatum (Ait.) Kuntze

International Common Names

  • English: earleaf nightshade; woolly nightshade
  • Spanish: ajicon (Cuba); prendedera (Cuba)
  • French: tabac marron
  • Portuguese: fona-de-porco (Azores); tabaqueira (Azores)

Local Common Names

  • Australia: tree tobacco; wild tobacco
  • Brazil: capoeira-branca; couvetinga; cuvitinga; fumeira; fumo-bravo
  • Cook Islands: rua 'va 'va
  • Cuba: tabaco cimarrón
  • New Zealand: flannel weed; keosine plant; tobacco weed
  • South Africa: bugtree; bugweed; groot bitterappel; luisboom; nbongobonga
  • Tonga: pula
  • USA/Hawaii: pua nana honua

EPPO code

  • SOLER (Solanum erianthum)
  • SOLMR (Solanum mauritianum)

Summary of Invasiveness

Top of page The South American tree S. mauritianum has been introduced to Africa, Australasia, India and islands of the Atlantic, Indian and Pacific Oceans. Worldwide, the worst infestations occur in the high rainfall regions of South Africa, where the weed invades natural forests, forestry plantations, riparian zones, urban open space and various disturbed areas. The weed's invasiveness is aggravated by extensive levels of fruiting and secondary distribution of the plant via seed dispersal by frugivorous birds. Negative attributes include displacing native vegetation, hindering commercial forestry activities, harbouring agricultural pests, poisoning livestock and providing health risks for humans. The plant is declared as a noxious weed in several countries. S. mauritianum is considered to be moderately invasive in the Cook Islands, but considerably more so in Australia, New Zealand and Tonga and is a declared weed (Category 1) in South Africa and a Class B noxious weed in New Zealand.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Spermatophyta
  •             Subphylum: Angiospermae
  •                 Class: Dicotyledonae
  •                     Order: Solanales
  •                         Family: Solanaceae
  •                             Genus: Solanum
  •                                 Species: Solanum mauritianum

Notes on Taxonomy and Nomenclature

Top of page The name Solanum mauritianum Scopoli is universally accepted for this weed which, despite its species name, is not native to Mauritius but to northeastern Argentina, southern Brazil, Uruguay and Paraguay (Roe, 1972). The plant belongs to the subgenus Brevantherum, one of several subgenera of Solanum (D'Arcy, 1972). Synonyms for this plant include Solanum auriculatum Ait., Solanum carterianum Rock., Solanum tabacifolium Vell. and Solanum verbascifolium var. auriculatum (Ait.) Ktze (Lorenzi, 1991; Kissmann and Groth, 1997). The plant is very closely related to other South American species like Solanum erianthum D. Don, Solanum granuloso-leprosum Dun., Solanum riparium Pers. and Solanum verbascifolium L. However, these species may well comprise geographical forms of a widespread and variable species complex (Neser, 1984), particularly since some share the same synonyms (Lorenzi, 1991; Kissmann and Groth, 1997). For example, although S. erianthum (= S. auriculatum, S. tabacifolium, S. mauritianum) and S. granuloso-leprosum (= S. verbascifolium var. auriculatum (Ait.), S. verbascifolium f. granuloso-leprosum (Dun.) Hassl.) are both listed as very similar, but distinct, species, some botanists regard them as synonyms of S. mauritianum, particularly since hybrids between these and S. mauritianum have been reported (Kissmann and Groth, 1997).

Description

Top of page The morphology of S. mauritianum has been described by several authors (Symon, 1981; Hinze, 1985; Lorenzi, 1991; Kissmann and Groth, 1997; Henderson, 2001). The plant is a shrub or small tree 2-4 m (up to 12 m) tall, branched above to form a rounded canopy. It is spineless and all parts (except older stems) are densely pubescent with sessile to long-stalked stellate hairs (trichomes), which are loose and floccose on young growth. The leaves are simple, alternate and elliptic and are more densely trichomate (and hence paler) on the lower surfaces. Leaves are up to 300 mm long and 120 mm wide on young vigorous growth, but are usually around 180 mm long and 70 mm wide on mature stems. The leaf margin is entire, the apex acuminate and the base cuneate and often oblique. The petioles are 30-90 mm long, each with 1-2 smaller auriculate leaves in the axils. These auriculate leaves are sessile, rounded, and sometimes absent from weak or distal shoots. When crushed, leaves produce an odour similar to that of diesel fuel. The flowers are perfect, actinomorphic and numerous in branched corymbs. The peduncles are up to 150 mm long to the first fork, with the pedicels 2-3 mm long. The calyx tube is short (2-3 mm long), while the lobes are narrowly triangular and 2-3 mm long. The corolla has a lilac blue to purple colour, with a pale star-shaped area at its base, and is stellate, 15-25 mm in diameter. There are five stamens inserted low on the corolla tube, with the filaments around 1 mm long and the oblong anthers 2-3.5 mm long and opening by terminal pores. The ovary is densely pubescent, with the style pubescent in the lower part and 5-7 mm long, and the stigma green and terminal. The green berries ripen to a dull yellow fruit which are succulent, globose, 10-15 mm in diameter and pubescent at least in early stages. The fruit are borne in compact terminal clusters. The seeds are numerous, flattened, 1.5-2 mm long, with the testa minutely reticulate and are self-compatible.

Plant Type

Top of page Broadleaved
Perennial
Seed propagated
Shrub
Tree
Vegetatively propagated
Woody

Distribution

Top of page The native range of S. mauritianum is considered to be north eastern Argentina, southern Brazil, Uruguay and Paraguay, although the plant has now also been introduced to Africa, Australasia, India and islands of the Atlantic, Indian and Pacific Oceans (Roe, 1972).

Distribution Table

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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.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasivePlantedReferenceNotes

Asia

IndiaRestricted distributionIntroduced Invasive Roe, 1972
JapanPresentIntroducedOhnishi and Katsuyama, 2011

Africa

CameroonPresentIntroduced Invasive Missouri Botanical Garden, 2003
ComorosPresentIntroduced Invasive Missouri Botanical Garden, 2003
KenyaPresentIntroduced Invasive Copeland and Wharton, 2006
MadagascarWidespreadIntroduced Invasive Roe, 1972; Jaeger and Hepper, 1986
MauritiusWidespreadIntroduced Invasive Roe, 1972; Jaeger and Hepper, 1986
RéunionWidespreadIntroduced Invasive Roe, 1972
South AfricaWidespreadIntroduced1862 Invasive Jaeger and Hepper, 1986; Henderson, 2001
SwazilandWidespreadIntroduced Invasive Henderson, 2001
UgandaPresentIntroduced Invasive Missouri Botanical Garden, 2003

North America

USAPresentPresent based on regional distribution.
-CaliforniaPresentIntroduced Invasive
-FloridaPresentIntroduced Invasive
-HawaiiPresentIntroduced Invasive

Central America and Caribbean

CubaPresentIntroduced Invasive Oviedo Prieto et al., 2012

South America

ArgentinaRestricted distributionNative Not invasive Natural Roe, 1972
BrazilWidespreadNative Invasive Lorenzi, 1991
-BahiaRestricted distributionNative Invasive Lorenzi, 1991
-Espirito SantoWidespreadNative Invasive Lorenzi, 1991
-Mato Grosso do SulRestricted distributionNative Invasive Lorenzi, 1991
-Minas GeraisWidespreadNative Invasive Lorenzi, 1991
-ParanaWidespreadNative Invasive Lorenzi, 1991
-Rio de JaneiroWidespreadNative Invasive Lorenzi, 1991
-Rio Grande do SulWidespreadNative Invasive Lorenzi, 1991
-Santa CatarinaWidespreadNative Invasive Lorenzi, 1991
-Sao PauloWidespreadNative Invasive Lorenzi, 1991
EcuadorPresentMissouri Botanical Garden, 2003
ParaguayWidespreadNative Not invasive Roe, 1972
PeruPresentMissouri Botanical Garden, 2003
UruguayWidespreadNative Not invasive Natural Roe, 1972

Europe

PortugalPresentPresent based on regional distribution.
-AzoresPresentIntroducedRoyal Botanic Garden Edinburgh, 2003

Oceania

AustraliaPresentPresent based on regional distribution.
-QueenslandRestricted distributionIntroduced Invasive Van Dyck, 1979; Symon, 1981
Cook IslandsPresentIntroduced Invasive Space & Flynn, 2003
FijiPresentIntroduced Invasive
French PolynesiaPresentIntroduced Invasive
Micronesia, Federated states ofPresentIntroduced Invasive Space et al., 2000
New CaledoniaPresentIntroduced Invasive Swarbrick, 1997
New ZealandWidespreadIntroduced1883 Invasive McGregor, 1999; Withers et al., 2002
Papua New GuineaWidespreadIntroduced Invasive Chadhokar, 1978
Solomon IslandsPresentIntroduced Invasive Swarbrick, 1997
TongaIntroduced, establishedIntroduced Invasive ISSG, IUCN SSC Invasive Species Specialist Group; Space and Flynn, 2001

History of Introduction and Spread

Top of page S. mauritianum was possibly introduced to Africa, Madagascar, Mauritius and India via the Portuguese trade routes in the early 16th century (Roe, 1972, 1979). In South Africa, the plant was first noted in KwaZulu-Natal Province around 1862 (Wright, 1904) and had become more widespread by 1881, culminating in its proclamation as a noxious weed in 1937 (Olckers and Zimmermann, 1991). The plant has since spread to most parts of South Africa, where it is particularly problematic in the eastern, higher rainfall regions of the country (Henderson, 2001). In New Zealand, S. mauritianum was first recorded in 1883 (Allan, 1940) but is now widely established in the northern areas of the North Island, with a restricted coastal distribution in the northern parts of the South Island (McGregor, 1999). The plant may have been promoted as an ornamental in New Zealand and in other parts of the world and its spread has also been influenced by native birds.

Risk of Introduction

Top of page The risk of further spread to countries where the weed is not currently naturalized does not appear to be high, because the plant is not normally spread via natural (non-biotic) means, agricultural practices nor accidental introduction. The greatest risks are probably posed by deliberate introductions for ornamental or commercial purposes. In South Africa, S. mauritianum is a declared weed (Category 1) stipulated under the Conservation of Agricultural Resources Act, while in New Zealand it is listed as a Class B noxious weed.

Habitat

Top of page S. mauritianum is adapted to a wide range of habitats, but is particularly prevalent in high-rainfall areas. In South Africa, the weed is mostly abundant in summer rainfall areas, but is also present in regions typified by winter and bimodal (spring and autumn) rainfall (Wells et al., 1986; Henderson, 2001). In South Africa, the plant occurs in a range of climatic conditions, from Mediterranean to coastal subtropical to high altitude temperate climates. Although the plant seems able to survive in most soil types, it thrives in soils that have high water retention. The weed is shade-tolerant to a certain degree and is particularly invasive in natural forests (particularly along the margins), forestry plantations, riparian zones and watercourses, savannas, roadsides, urban open space and any other disturbed areas (e.g. along the course of electricity pylons etc.) (Henderson, 2001). In Hawaii, the weed is naturalized on slopes and ridges in disturbed wet forest.

Habitat List

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CategorySub-CategoryHabitatPresenceStatus
Terrestrial
 
Terrestrial – ManagedCultivated / agricultural land Present, no further details Harmful (pest or invasive)
Managed forests, plantations and orchards Present, no further details Harmful (pest or invasive)
Disturbed areas Present, no further details Harmful (pest or invasive)
Rail / roadsides Present, no further details Harmful (pest or invasive)
Urban / peri-urban areas Present, no further details Harmful (pest or invasive)
Terrestrial ‑ Natural / Semi-naturalNatural forests Present, no further details Harmful (pest or invasive)
Natural grasslands Present, no further details Harmful (pest or invasive)
Riverbanks Present, no further details Harmful (pest or invasive)
Wetlands Present, no further details Harmful (pest or invasive)
Littoral
Coastal areas Present, no further details Harmful (pest or invasive)

Hosts/Species Affected

Top of page S. mauritianum does not normally invade agricultural land. However, in South Africa, the plant is a major problem in commercial forestry plantations where it competes with seedlings of Pinus species and inhibits their growth (Hinze, 1985). In South Africa, the plant is mostly regarded as an environmental weed which displaces native vegetation. Natural forests are particularly susceptible to invasion, largely because fruit-eating birds, which are the main dispersers of the seeds of forest plants, have altered their diet to the fruit of S. mauritianum because of its greater abundance and predictability as a food source. Indeed, certain native forestry plants (e.g. Ocotea bullata) have become endangered because their normal dispersal agents (e.g. Rameron pigeons) no longer disperse their seeds (Oatley, 1984; Pooley, 1993; Scott-Shaw, 1999).

Host Plants and Other Plants Affected

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Plant nameFamilyContext
Eucalyptus spp.MyrtaceaeOther
Ocotea bullataLauraceaeWild host
Pinus sp. (pine)PinaceaeMain

Growth Stages

Top of page Post-harvest, Seedling stage, Vegetative growing stage

Biology and Ecology

Top of page Genetics

The chromosome number is n=12 (2n=24) (Symon, 1981). Hybridization with closely related species like S. erianthum and S. granuloso-leprosum has been suspected in South America, although the latter species may turn out to be synonyms of S. mauritianum, as regarded by some botanists (Kissmann and Groth, 1997).

Physiology and Phenology

In both its native and introduced habitats, the plant produces flowers and fruit throughout the year. Seeds appear to require a 3-month period of after-ripening under dry conditions before they will germinate, but seed viability is high, with 98% reported in South Africa (Hinze, 1985). Germination requirements are highly variable, but S. mauritianum seeds require the presence of both light and alternating temperatures for optimum germination (Campbell and Staden, 1983; Campbell, 1990; Campbell et al., 1992; Campbell and Staden, 1994). The seeds do not appear to have an extended period of dormancy, preventing the formation of long-lived soil seed banks (Hinze, 1985). Germination of seeds stored in soil is stimulated by fire. The various factors influencing germination ensures that seedling emergence is sporadic and occurs over a prolonged period (Campbell, 1990). Seedlings that become established in summer are able to flower and fruit by autumn. The plant has a high growth rate and seedlings are able to grow to a height of several metres within 2-3 years. Established plants that are felled will regrow rapidly and can produce flowers within 12 months (Denny, 1999). It is a short lived tree and mature plants begin to die after 15 years.

Reproductive Biology

S. mauritianum propagates primarily via seeds which are dispersed by frugivorous birds, bats and monkeys. Pollination is primarily via insects and plants are able to flower when 1-2 years old, with some 20-80 berries borne on each inflorescence, each berry containing about 150 seeds (Hinze, 1985). The plant produces flowers and bears fruit at regular intervals throughout the year, enabling a single plant to produce excessive numbers of seeds. Plant populations are not typified by long-lived soil seed banks and most seeds in the seed bank are damaged by insects and pathogens (Denny, 1999). However, the excessive numbers of seeds produced annually ensure that there are sufficient seedlings to augment plant populations and promote the weed's spread. The plant also propagates vegetatively when mechanically damaged by cutting or uprooting and pieces of root remaining in the soil will regrow (Hinze, 1985).

Environmental Requirements

Observations in South Africa suggest that S. mauritianum is adapted to a wide range of habitats, climates and environmental conditions (Wells et al., 1986). The plant does not normally persist in arid conditions, but thrives in moist habitats and in high-rainfall areas. In South Africa, the plant tolerates all seasonal rainfall patterns (Wells et al., 1986), with summer rainfall areas the worst affected. Conditions suitable for the plant include coastal and low-altitude subtropical climates, but also high-altitude warm temperate and Mediterranean climates. The plant seems to tolerate most soil types, but thrives in those with high water retention. The plant is also able to tolerate low temperatures and occurs in areas that are subject to light frost. The weed is both frost-tolerant and shade-tolerant to a certain degree. Disturbances in both transformed habitats (e.g. fence lines, forestry plantations) and natural vegetation appear to trigger invasion.

Associations

In South Africa, the fruit of S. mauritianum provide winter food for the Mediterranean fruit fly (Ceratitis capitata) and Natal fruit fly (Ceratitis rosa), which are pests of several species of deciduous and tropical fruit throughout the country. It is also likely that the plant acts as a host for several diseases of cultivated Solanaceae (e.g. Tobacco mosaic virus).

Latitude/Altitude Ranges

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Latitude North (°N)Latitude South (°S)Altitude Lower (m)Altitude Upper (m)
0 0 0 0

Air Temperature

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Parameter Lower limit Upper limit
Absolute minimum temperature (ºC) -5
Mean annual temperature (ºC) 15 22
Mean maximum temperature of hottest month (ºC) 25 32
Mean minimum temperature of coldest month (ºC) 5 12

Rainfall

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ParameterLower limitUpper limitDescription
Dry season duration24number of consecutive months with <40 mm rainfall
Mean annual rainfall5001500mm; lower/upper limits

Rainfall Regime

Top of page Bimodal
Summer
Winter

Soil Tolerances

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Soil drainage

  • free
  • impeded

Soil reaction

  • acid
  • alkaline
  • neutral

Soil texture

  • heavy
  • light
  • medium

Special soil tolerances

  • shallow

Notes on Natural Enemies

Top of page The natural enemies of S. mauritianum in its native South American countries have been documented following surveys for potential biological control agents by South African entomologists (Neser et al., 1990; Olckers, 1999; Olckers et al., 2002). More than 80 phytophagous species were collected on S. mauritianum and closely related plants, but very few of these were candidates for biocontrol (Neser et al., 1990). The impact of natural enemies in South America is exemplified by the relatively low levels of fruiting that are caused by flower-feeding insects. These and other leaf-feeding and stem-boring species inflict considerable damage to native S. mauritianum populations. The most promising candidates for biocontrol were reviewed by Olckers (1999). Although 15 insect species were imported into quarantine in South Africa for observations and screening, only one has been released while another has been proposed for release. Refer to the section on Biological Control for more information.

Means of Movement and Dispersal

Top of page Natural Dispersal (non-biotic)

The weed does not normally spread via non-biotic means, although the seeds of plants growing along watercourses and riparian zones could be spread by water.

Vector Transmission (biotic)

Fruit are produced in abundance throughout the year and are thus a predictable food source for fruit-eating birds and mammals. The weed propagates primarily by seeds which, in South Africa, are dispersed by frugivorous birds, bats and monkeys that consume the ripe fruit and facilitate long-distance spreading of the weed (Hinze, 1985). Birds have also been reported to consume the fruit in Australia (Van Dyck, 1979) and New Zealand (McGregor, 1999). Also, birds could indirectly disseminate seed over long distances as birds could potentially deposit seed onto agricultural produce intended for transportation to new areas. In situations where pastures and rangelands may be invaded, livestock does not normally consume the fruits and is thus unlikely to disseminate ingested seeds.

Agricultural Practices

There are no recorded instances of the weed being spread by agricultural practices, since it does not normally invade croplands, although seed could be spread by attachment to vehicles' tyres.

Accidental Introduction

There are no records of the weed being spread by means of trade or transport, although the potential for this may well exist.

Intentional Introduction

Deliberate introductions of the plant may well have occurred globally for ornamental purposes, since the plant has attractive mauve/purple flowers and the copious amounts of fruit produced attract birds in residential gardens. Seed is still available from a number of commercial mail order companies (e.g. Malkmus, 2003). However, ornamental usage is prohibited in many countries (e.g. South Africa, New Zealand) where the weed is invasive. Although extracts of the plants could be utilized commercially for the synthesis of corticosteroid drugs, there are no records of deliberate introductions for this purpose.

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
Leaves seeds
True seeds (inc. grain) seeds
Plant parts not known to carry the pest in trade/transport
Bark
Bulbs/Tubers/Corms/Rhizomes
Flowers/Inflorescences/Cones/Calyx
Fruits (inc. pods)
Growing medium accompanying plants
Roots
Seedlings/Micropropagated plants
Stems (above ground)/Shoots/Trunks/Branches
Wood

Impact Summary

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CategoryImpact
Animal/plant collections None
Animal/plant products None
Biodiversity (generally) Negative
Crop production None
Environment (generally) Negative
Fisheries / aquaculture None
Forestry production Negative
Human health Negative
Livestock production None
Native fauna None
Native flora Negative
Rare/protected species Negative
Tourism None
Trade/international relations None
Transport/travel None

Impact

Top of page Although S. mauritianum can, but does not normally, invade agricultural land, pastoral land is invaded which may lead to loss of grazing potential. In South Africa, the plant is a major problem in commercial forestry plantations where it competes with seedlings of pine trees (Pinus species), retarding their growth and that of young trees where deformation of the stems occurs (Hinze, 1985). In older stands, the weed causes problems in silvicultural and harvesting operations where repeated chemical and mechanical control operations increase the costs of plantation management. The weed grows less vigorously under a canopy cover than in open areas and is thus more problematic during the establishment phases of forestry operations (Hinze, 1985). Also, in South Africa, the fruit provide winter food for the Mediterranean fruit fly (Ceratitis capitata) and Natal fruit fly (Ceratitis rosa), which are pests of several species of deciduous and tropical fruit throughout the country. Although the plant is not normally consumed by livestock, there are reports of fatal poisoning of pigs and cattle in Queensland, Australia (Everist, 1974; Van Dyck, 1979).

Environmental Impact

Top of page In South Africa, the plant is a major environmental weed and is classified as a "transformer species" which displaces native vegetation (Wells et al., 1986; Henderson, 2001). Dense stands are able to inhibit the growth of other plant species through overcrowding and shading. Natural forests are particularly susceptible to invasion, largely because fruit-eating birds (notably Rameron pigeons), which are the main dispersers of the seeds of forest plants, have altered their diet to the fruit of S. mauritianum (Oatley, 1984) to the detriment of the former plants. Other habitats that are susceptible to invasion include riparian zones and watercourses, savanna and any other disturbed sites (e.g. forest gaps caused by natural tree mortality).

Impact: Biodiversity

Top of page Although the impact of S. mauritianum on native biodiversity has not been quantified, dense stands of the plant clearly exclude native vegetation and their associated organisms, notably host specific herbivorous insects (Olckers and Hulley, 1991). In South Africa, the weed invades natural areas, including several proclaimed nature reserves throughout the country. Also, in South Africa, seed dispersal of several native plants has been adversely affected because the avian dispersive agents have switched their diet to the fruit of S. mauritianum (Oatley, 1984). In particular, Ocotea bullata (stinkwood) has become endangered in natural forests because of inappropriate utilization and the fact that Rameron pigeons no longer disperse their seeds adequately (Pooley, 1993; Scott-Shaw, 1999).

Social Impact

Top of page The plant invades urban areas via frugivorous birds which deposit seeds in residential gardens. In South Africa, alien plant legislation dictates that fines may be imposed if property owners do not remove this plant from their gardens (Henderson, 2001). All parts of the plant are toxic to humans, especially the green berries that are rich in alkaloid chemicals. The fine hairs (trichomes) on the stems and leaves can be an irritant and can cause respiratory problems (Henderson, 2001), especially when they are dislodged during mechanical clearing operations.

Risk and Impact Factors

Top of page Invasiveness
  • Invasive in its native range
  • Proved invasive outside its native range
  • Highly adaptable to different environments
  • Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
  • Highly mobile locally
  • Has high reproductive potential
  • Has propagules that can remain viable for more than one year
Impact outcomes
  • Damaged ecosystem services
  • Ecosystem change/ habitat alteration
  • Negatively impacts agriculture
  • Negatively impacts human health
  • Negatively impacts animal health
  • Negatively impacts tourism
  • Reduced amenity values
  • Reduced native biodiversity
Impact mechanisms
  • Competition - monopolizing resources
  • Pest and disease transmission
Likelihood of entry/control
  • Highly likely to be transported internationally deliberately

Uses

Top of page With the possible exception of the ripe fruit, S. mauritianum has no fodder value and plants are generally avoided by grazing animals. However, the weed has been suggested as a 'nursery plant' in countries where its invasiveness has been limited (e.g. Australia), since it supposedly can provide a protective environment for native vegetation to germinate and grow underneath (Van Dyck, 1979). However, this should not be advised as it will pertain only to situations that are marginal for the plant - healthy stands of S. mauritianum will normally shade out native plants growing beneath them (as experienced in South Africa). In rare situations, the fruit may be a valuable food source for native bird species, although these tend to facilitate long-distance dispersal and further invasion of the weed. The most use important use for S. mauritianum concerns its potential for the synthesis of corticosteroid drugs, the precursors of which (e.g. solasodine) are extracted from the unripe fruit of the plant. Although this possibility was investigated in South Africa (Campbell, 1990; Campbell and Staden, 1990), commercial production was never initiated and it is uncertain whether this has occurred elsewhere in the world.

Uses List

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Materials

  • Poisonous to mammals

Medicinal, pharmaceutical

  • Source of medicine/pharmaceutical

Similarities to Other Species/Conditions

Top of page In its native countries, several congeneric species appear very similar to S. mauritianum. These include Solanum erianthum, S. granuloso-leprosum, S. riparium and S. verbascifolium. Also, in some countries where the plant has been introduced, some congeneric native species have similarities. In Australia, the native S. stelligerum and S. densevestitum (devil's needles) appear similar to S. mauritianum (Symon, 1981). Both native species have purple flowers and furry grey-green leaves, but the leaves are smaller and narrower than those of S. mauritianum. Both plants are also smaller, growing to around 1 m in height. A distinguishing feature of S. stelligerum is the prickles on the stems. In South Africa, the native S. giganteum has been confused with the weed, although it can easily be distinguished by its thorny stems, shiny green leaves with powdery white undersides, and smaller berries which turn red when ripe.

Prevention and Control

Top of page Cultural Control

Cultural control methods, e.g. burning or oversowing with grass species to provide competition, are not normally used against S. mauritianum. Indeed, in forestry situations, the burning of leaf litter is discouraged as the forest floor mulch has an inhibiting effect on seed germination (Hinze, 1985).

Mechanical Control

Manual control methods, which are largely aimed at the prevention of fruiting, involve the felling of large trees and slashing of smaller plants, ring-barking of trees and hand-pulling of seedlings (Denny, 1999). Seedlings less than 1 m tall can be hand-pulled in soft, moist soil, but roots that break off will coppice. Also, the grubbing out of large plants with mattocks is often unsuccessful as severed roots will initiate regrowth (Hinze, 1985). Felling and slashing by itself is insufficient as the plants will resprout to form multi-stemmed thickets which are more difficult and more expensive to control. As a result, felling and slashing must be accompanied by herbicidal applications. Ring-barking is effective for controlling small infestations, but is labour-intensive (Little, 1980; McGregor, 1999).

Chemical Control

Herbicides are currently the most effective means of controlling S. mauritianum, since the plant is easily killed with herbicides. Application methods include: (i) foliar sprays for seedlings and regrowth that follows felling or slashing, (ii) basal-stem treatments to the lower stems and root crowns of trees, (iii) cut-stump applications following felling or slashing and (iv) soil applications (Denny and Goodall, 1992; Denny, 1999). In South Africa, several chemicals are registered for use against S. mauritianum and include glyphosate, sulfosate, triclopyr and fluroxypyr for foliar applications, triclopyr and fluroxypyr for basal-stem treatments, triclopyr and imazapyr for cut-stump applications and tebuthiuron for soil applications (Denny, 1999; Grobler et al., 2000). Soil applications are not recommended when the plants are close to crops or plantations, while cut-stump applications of imazapyr are not advised in plantations of Eucalyptus species. The most popular methods are basal-stem and cut-stump applications. Herbicides are best applied during the weed's growing season (Hinze, 1985).

Biological Control

Biological control has only been attempted in South Africa, where the sap-sucking lace bug Gargaphia decoris (Tingidae), which was released in 1999, is so far the only agent that has been used (Olckers, 1999, 2000). However, this insect has proved ineffective to date, largely because of its failure to establish at many release sites and its inability to sustain high population densities throughout the year. Permission for the release of a second agent, the flower bud-feeding weevil Anthonomus santacruzi (Curculionidae) that prevents fruiting, is currently being sought in South Africa (Olckers, 2003). Besides South Africa, only New Zealand has considered biological control of S. mauritianum (Withers et al., 2002). This plant has proved to be a difficult target for biological control because of closely related cultivated and native plants in the genus Solanum, which have made it difficult to obtain clearance for the release of biological control agents.

Integrated Control

Integrated control is currently confined to the use of herbicides in conjunction with mechanical clearing. However, it is believed that biological control has an important role to play, notably in reducing the weed's excessive seed production and recruitment of seedlings and thereby rendering conventional follow-up operations more sustainable. In South Africa, follow-up operations are essential and work needs to be continued for at least 3 years once initiated at a particular site. In particular, operations involve three stages which include (i) killing standing trees to prevent further seed production, (ii) removing seedlings that regenerate from the seed-bank and (iii) encouraging native plants to smother the seedlings (Denny, 1999). It is important that seedlings be controlled annually, preferably at the end of summer.

References

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