Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Datasheet

Gunnera tinctoria
(giant rhubarb)

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Datasheet

Gunnera tinctoria (giant rhubarb)

Summary

  • Last modified
  • 06 November 2018
  • Datasheet Type(s)
  • Invasive Species
  • Preferred Scientific Name
  • Gunnera tinctoria
  • Preferred Common Name
  • giant rhubarb
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Spermatophyta
  •       Subphylum: Angiospermae
  •         Class: Dicotyledonae
  • Summary of Invasiveness
  • Gunnera tinctoria, a large leaved plant from Chile growing up to 2 m in height, became a very popular ornamental species in gardens and parks in temperate areas from the middle of the nineteenth century. By the 1...

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Pictures

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PictureTitleCaptionCopyright
Gunnera tinctoria (giant rhubarb); habit, on the island of Valentia off the coast of SW Kerry, Republic of Ireland. September, 2013
TitleHabit
CaptionGunnera tinctoria (giant rhubarb); habit, on the island of Valentia off the coast of SW Kerry, Republic of Ireland. September, 2013
Copyright©Andrew Praciak-2013
Gunnera tinctoria (giant rhubarb); habit, on the island of Valentia off the coast of SW Kerry, Republic of Ireland. September, 2013
HabitGunnera tinctoria (giant rhubarb); habit, on the island of Valentia off the coast of SW Kerry, Republic of Ireland. September, 2013©Andrew Praciak-2013
Gunnera tinctoria (giant rhubarb); habit, on the island of Valentia off the coast of SW Kerry, Republic of Ireland. September, 2013
TitleHabit
CaptionGunnera tinctoria (giant rhubarb); habit, on the island of Valentia off the coast of SW Kerry, Republic of Ireland. September, 2013
Copyright©Andrew Praciak-2013
Gunnera tinctoria (giant rhubarb); habit, on the island of Valentia off the coast of SW Kerry, Republic of Ireland. September, 2013
HabitGunnera tinctoria (giant rhubarb); habit, on the island of Valentia off the coast of SW Kerry, Republic of Ireland. September, 2013©Andrew Praciak-2013

Identity

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Preferred Scientific Name

  • Gunnera tinctoria (Molina) Mirb. (1805)

Preferred Common Name

  • giant rhubarb

Other Scientific Names

  • Gunnera chilensis Lam. (1789)
  • Gunnera scabra Ruiz & Pav.
  • Panke tinctoria Molina (1782)

International Common Names

  • English: Chilean gunnera; Chilean rhubarb

Local Common Names

  • Chile: ape ape; nalca; pangue; raway
  • Germany: Chilenische Gunnera

Summary of Invasiveness

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Gunnera tinctoria, a large leaved plant from Chile growing up to 2 m in height, became a very popular ornamental species in gardens and parks in temperate areas from the middle of the nineteenth century. By the 1930s, and more extensively since the 1960s, it became naturalized to form dense monospecific stands on the west coast of Ireland, southwest England, the west coast of Scotland, the Azores, the coast of California and New Zealand where dense local infestations are found on coastal cliffs. Habitats with moderate to heavy rainfall and frost-free conditions for most of the year and relatively small variations in temperature are ideal for plants to naturalize. The species can spread from rhizomes discarded from gardens and from seed disseminated by birds and is a threat to native vegetation. Its sale and further cultivation is now prohibited in Ireland and New Zealand where eradication programmes are underway.

 

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Spermatophyta
  •             Subphylum: Angiospermae
  •                 Class: Dicotyledonae
  •                     Order: Haloragales
  •                         Family: Gunneraceae
  •                             Genus: Gunnera
  •                                 Species: Gunnera tinctoria

Notes on Taxonomy and Nomenclature

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Numerous taxonomic affinities have been suggested for the genus Gunnera. The history of these and current understanding of the phylogeny has been reviewed by Fuller and Hickey (2005). Gunnera was placed in the monogeneric family the Gunneraceae, by the 1830s but other taxonomists later argued that it should be placed in the Haloragaceae because the genus has a distinctive pseudo-polystelic vascular system, which has been claimed to indicate an aquatic ancestry, such as from the Haloragaceae. However, striking differences between Gunnera and haloragaceous taxa have been noted by numerous researchers particularly the floral vasculature of Gunnera considered to be too reduced to provide a useful comparison with Haloragaceae. Nevertheless, Gunneraceae has remained associated with Haloragaceae in much of the taxonomic literature by placement in the same order, despite a long list of character differences between the two families. The International Plant Names Index records this species as Gunnera tinctoria (Molina) Mirb, as a species of the Gunneraceae, based on the treatment of the species by Mirbel (1805). The species name was derived from the basoionym Panke tinctoria Molina, a member of the Saxifragaceae. This nomenclature is also followed by the Integrated Taxonomic Information System. Both Flora Europea and Tropicos (Missouri Botanical Gardens) however place the genus in the Haloragaceae, referring to the species as G. tinctoria Mirb.

This monogeneric family, the Gunneraceae, comprises about 50 species, which show great variation in size. The larger, rhubarb-like, stand forming species (up to 6 m high) are typical of areas ranging from Hawaii to Central America and South America, whereas smaller, more slender species are found in New Zealand, South-East Asia and the southernmost parts of South America. The eleven endemic species of New Zealand are all small, often 10 cm high, and form stolons, whereas the larger species are rhizomatous. Gunnera is traditionally divided into six subgenera that are largely geographically distinct (Fuller and Hickey, 2005). G. tinctoria is included in the sub-genus Panke. This consists of more than 19 species in South America and the Hawaiian and Juan Fernandez Islands These species produce leaves up to 2 meters across, supported by erect petioles that arise near the apex of a pachycaul. Infloresences are large (up to 2 m long) panicles of hermaphroditic, but occasionally, unisexual, flowers. The subgenus Panke lacks stolons.

G. tinctoria or giant rhubarb is not related to rhubarb (Rheum rhabarbarum), but as its English name implies it is similar in appearance.

Description

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G. tinctoria is a large herbaceous plant with thorny leaves and stems that forms dense colonies and shades out other plants. Williams et al. (2005) provide the following description: “It is deciduous, with short, stout, horizontal rhizomes which give rise to stout petioles up to 1000 (1500), 1 mm x 45 mm that are studded with short reddish prickles. The leaf lamina measures up to about 0.8 m x 1.0 m with 5–7 lobes. It is very coriaceous, and hairy beneath, especially on the veins. Massive over-wintering buds—up to 250 mm long—accumulate on the rhizomes and they are covered in pinkish, pinnatisect scales that extend to the broad leaf midribs. The flowers are borne on panicles less than or equal to 1 m long; usually three or four per plant. Individual flowers are densely packed, sessile, apetalous, with minute sepals, and only about 1 mm long. Style length is slightly less than the ovary. The drupes are reddish, oblong, and 1.5 mm–2 mm long. Each contains a single ovoid and flanged seed of 1.2 mm x 1–1.5 mm diameter, weighing 4 mg. The hundreds of fruit are regularly arranged and densely packed on the infructescence”.

Plant Type

Top of page Broadleaved
Herbaceous
Perennial
Seed propagated

Distribution

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G. tinctoria is reported as native on both sides of the Andes from Colombia to Chile (Williams et al., 2005) but has an origin in southern Chile between 36 and 42° south. Because of its striking appearance the species was widely introduced as an ornamental, planted by lakes, streams and in bog gardens, initially in North America and Europe but later in New Zealand and Australia. From these introductions it has become naturalised as a garden escape. In UK it is now common in the moist south-west of the country in the Scilly Isles and Cornwall, but is also found in Devon, Dorset, Somerset, Oxfordshire, Berkshire, Surrey and in East Anglia, west to North Wales, Central England, Yorkshire and on the west coast of mainland Scotland and a number of the Western Isles (see Global Biodiversity Information Facility (2008) for records). There is also a record of the plant in the east coast of Scotland. In UK the plant ranges from 49.9 to 58.2° north. G. tinctoria is currently considered invasive on the west coast of Ireland where the most extensive colonies are found west of County Mayo and County Galway (Hickey and Osborne, 2001). These are areas where freezing temperatures are uncommon because of the Gulf Stream current; its eastern expansion appears to be related to intolerance of low temperatures. However it is also found on the east coast of Ireland but it is not considered invasive here (Invasive Species Ireland, 2008).

Elsewhere in Europe the species has proved a successful invader of the Azores archipelago, particularly in San Miguel Island and is also naturalized in France and Spain (Sanz-Elorza et al., 2001; Williams et al., 2005).

In USA it is currently restricted to coastal counties of California (Calflora, 2008). The species is now widespread in New Zealand (Williams et al., 2005) having been introduced as a waterside plant in parks, botanic gardens, and in large public and private gardens throughout the country. It has been found naturalised in Hawke’s Bay, Taranaki, Wanganui, Banks Peninsula, Dunedin and Stewart Island. Williams et al. (2005) show occurrences along the western coasts of both North and South Islands. In these areas it grows from sea level to 380 m above sea level. The areas where it is present cover a range of summer temperatures but lack extremes, and they have abundant and relatively even, year-round precipitation.

The position in Australia is less clear. ISSG (2008) cites “Department of Environment and Conservation” indicating that this is an Alien Invasive Plant in New South Wales. However, a fact sheet warning of the dangers of introducing the species, prepared by the State of Victoria Department of Primary Industries in December 2007 indicated that G. tinctoria, “is not known to have naturalized in Victoria or Australia” (Plant and Robertson, 2008).

Osborn (2006) provides evidence to suggest that G. tinctoria population increases in Britain and Ireland, north west Europe, North America, New Zealand and the Azores have occurred at a similar time, during the early 1960s, irrespective of geographical location. Analysis of environmental correlates associated with the current/past distribution of this species shows that this has been associated with increases in rainfall and temperature and is largely independent of edaphic factors. Future projections, based on current climatic data, suggest that the distribution will increase at all current locations, as well as proposing that new areas may become invaded.

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 ReportedInvasiveReferenceNotes

North America

USAPresentPresent based on regional distribution.
-CaliforniaPresent, few occurrencesIntroduced Invasive McClintock, 1993; EPPO, 2014Central Coastal areas: Marin and San Francisco countries

South America

ArgentinaPresentNative Not invasive Global Biodiversity Information Facility, 2008; EPPO, 2014
BoliviaPresentEPPO, 2014
ChilePresentNative Not invasive Marticorena and Quezada, 1985; EPPO, 2014
ColombiaPresentEPPO, 2014
EcuadorPresentEPPO, 2014
PeruPresentEPPO, 2014
VenezuelaPresentEPPO, 2014

Europe

FrancePresentIntroduced Invasive Williams et al., 2005; EPPO, 2014
IrelandLocalisedIntroduced Invasive Alien Plants in Ireland, 2008; EPPO, 2014Noted as invasive since mid to late 1930s. South Kerry-West Cork-Waterford-North Tipperary-West Galway-Dublin-West Mayo-Sligo-East Donegal-Down-Antrim-Londonderry
PortugalPresentPresent based on regional distribution.
-AzoresLocalisedIntroduced Invasive WWF, 2008; EPPO, 2014Particularly Isle de San Miguel
SpainPresentIntroduced Not invasive Sanz-Elorza et al., 2001
UKLocalisedIntroduced1849 Invasive Global Biodiversity Information Facility, 2008Cornwall and Isles of Scilly through Devon, Somerset, Dorset to East Anglia, West Wales, Central England to West Scotland
-England and WalesPresentEPPO, 2014
-Northern IrelandRestricted distributionEPPO, 2014
-ScotlandPresentEPPO, 2014

Oceania

AustraliaAbsent, no pest recordEPPO, 2014
-New South WalesPresent, few occurrencesIntroduced Invasive ISSG, 2008Rare out of cultivation
New ZealandPresentIntroduced1968 Invasive Williams et al., 2005; EPPO, 2014North and South Island. Particularly Hawke's Bay, Taranaki, Wanganui, Banks Peninsula, Dunedin and Stewart Island

History of Introduction and Spread

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All cases of introduction and spread of G. tinctoria have been through planting as an ornamental followed by the species becoming naturalized as a garden escape. In Britain and Ireland this species was introduced into cultivation around 1850, but was not recorded in the wild until the early 1900s indicating an establishment phase of 60 years. Significant records of this species in the wild were not, however, found until the 1950s indicating a further lag phase of 40 years before any significant spread (Osborne and Gioria, 2005). The earliest known record of a naturalized stand in Ireland is from 1939, at Killary Harbour in County Mayo, although it is likely that it had been naturalized prior to this. Based on pollen identification in conjunction with analysis of soil sequences suggests it could have been present in Ireland for 100 years (Hickey and Osborne, 2001). G. tinctoria was first collected in the wild in New Zealand in 1968. By 1988 it had been found naturalised in Hawke’s Bay, Taranaki, Wanganui, Banks Peninsula, Dunedin and Stewart Island and has continued to spread (Williams et al., 2005).

 

Introductions

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Introduced toIntroduced fromYearReasonIntroduced byEstablished in wild throughReferencesNotes
Natural reproductionContinuous restocking
Ireland Chile 1850s Ornamental purposes (pathway cause) Yes Hickey and Osborne (2001)
New Zealand Chile ? Ornamental purposes (pathway cause) Yes Williams et al. (2005)
UK Chile 1850s Ornamental purposes (pathway cause) Yes FAO (2008)

Risk of Introduction

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G. tinctoria is a popular ornamental species, particularly for larger gardens and landscaping by streams, ponds and other water features. It has therefore become widely available through the horticultural trade since being introduced to cultivation during the 1800s. In a suitable habitat and climate it can be spread accidentally beyond gardens in garden waste or contaminated soil. Seeds are also spread in the faeces of birds e.g. blackbird in New Zealand (Williams et al., 2005). The species is readily available through the nursery trade in many countries including Ireland and UK and can be ordered via the internet. It was also available via wholesale nurseries in New Zealand at least until the late 1990s.

The horticultural trade in Ireland has introduced a voluntary ’Code Of Practice‘ which expects member traders to “avoid selling non-native plants that are known to be invasive, and are already posing a threat to native biodiversity or if invasive non-native plants are sold, to ensure they are clearly and correctly named, and labeled to identify the dangers to the wider environment if these plants were to escape from gardens or horticultural premises” (Invasive Species Ireland, 2008). Following concerns at the extent of invasions in County Mayo, the Department of Nationa Parks and Wild Life Service planed to use Section 52(6)(a) of the Wildlife Act 1976 to make regulations in 2008, under which possession or introduction of Gunnera will be prohibited.

The UK Department for Environment, Farming and Rural Affairs published a consultation document on restricting the cultivation or sale of non-native species in November 2007 as part of a review of the Wildlife and Countryside Act, 1981 (www.defra.gov.uk). The proposal is to add G. tinctoria to the list of species whose introduction into the wild is prohibited and to ban further sales of plants. G. tinctoria is classed as an ‘unwanted organism’ under the Biosecurity Act 1997 of New Zealand and is included on the National Pest Plant Accord List making selling, propagating or distributing it illegal throughout the country (Williams et al., 2005). It is now included on regional Pest Plant Management Strategies developed by regional councils. For example in Taranaki, it was made illegal to propagate, distribute or sell the species in the region, and it has been obligatory since July 1, 2003 for land occupiers throughout Taranaki to destroy it (Law, 2003).

Although it is considered as high risk for the State of Victoria and other areas of south eastern Australia the plants and seed of the species are permitted entry into Australia and are not listed as noxious by any state laws (Plant and Robertson, 2008). G. tinctoria is not scheduled as a noxious weed in USA.

Habitat

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Williams et al. (2005) is the most comprehensive source of information on habitat. In its native range in Chile, G. tinctoria grows on forest margins adjacent to wetland areas, stream-sides and, particularly, on bluffs and talus slopes. In Ireland it is now found on coastal cliffs, waterways, roadsides, wet meadows and derelict gardens and fields. On the west coast of New Zealand the species is common along stream banks and ’wet cliffs‘ (Williams et al., 2005).

Habitat List

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CategoryHabitatPresenceStatus
Littoral
Coastal areas Principal habitat Harmful (pest or invasive)
Terrestrial-natural/semi-natural
Riverbanks Principal habitat Harmful (pest or invasive)
Rocky areas / lava flows Principal habitat Harmful (pest or invasive)

Biology and Ecology

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Genetics

The chromosome number of G. tinctoria has been determined as 2n = 34 (Dawson, 1983). No information on genetic variation or hybridization in this species has been found. 

Reproductive Biology  

G. tinctoria reproduces sexually via seed as well as vegetatively, from root fragments, rhizomes and even leaf cuttings. Birds and small mammals find the tiny red fruit nutritious and assist greatly in seed dispersal. Plants flower after about 4 to 5 years under New Zealand conditions (Williams et al., 2005) and flowers are either female or hermaphrodite on the same plant and are, therefore, gynomonoecious (Webb et al., 1988). Hymenopterous insects, particularly bees, are probably the main pollinators. A single G. tinctoria may produce 250,000 seeds in a year (Law, 2003). Fresh seed germinates readily and shows no dormancy (Williams et al., 2005).

Physiology and Phenology  

Generally the species lies dormant under winter conditions in Ireland, New Zealand and UK (Williams et al., 2005). It is deciduous in areas with harsh winter frosts. However active leaves may be maintained in some areas of New Zealand.

Nutrition  

The genus Gunnera is unique in the plant kingdom by acquiring nitrogen through symbiosis with nitrogen-fixing cyanobacterium, Nostoc punctiforme (Osborne et al., 1991). The structurally unique stem glands of Gunnera function as the conduit through which cyanobacteria infect the host. As the genus Nostoc is cosmopolitan and common, it is likely to be present in the wet habitats in which Gunnera grows (Bergman and Osborne, 2002).

Environmental Requirements  

These aspects have been covered elsewhere in this data sheet. Further details are given in Williams et al. (2005).

Climate

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ClimateStatusDescriptionRemark
Cf - Warm temperate climate, wet all year Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year
Cs - Warm temperate climate with dry summer Tolerated Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers

Latitude/Altitude Ranges

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Latitude North (°N)Latitude South (°S)Altitude Lower (m)Altitude Upper (m)
58 35 0 0

Air Temperature

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Parameter Lower limit Upper limit
Mean annual temperature (ºC) 10.4 13.5
Mean maximum temperature of hottest month (ºC) 14.0 17.6
Mean minimum temperature of coldest month (ºC) 5.9 6.9

Rainfall

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ParameterLower limitUpper limitDescription
Mean annual rainfall10101972mm; lower/upper limits

Rainfall Regime

Top of page Summer
Uniform

Soil Tolerances

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Soil drainage

  • seasonally waterlogged

Soil reaction

  • acid

Soil texture

  • heavy
  • medium

Notes on Natural Enemies

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Williams et al. (2005) found no information about predators in their review of the literature. In New Zealand, the plants relative lack of insect pests and diseases made the species attractive to horticulturalists.

Means of Movement and Dispersal

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Natural Dispersal (Non-Biotic)

As G. tinctoria grows along the waters edge, the small seeds are washed into watercourses, further dispersing their seed. The large rhizome can break off the plant and roll down slopes or be washed along watercourses, take root and grow (Williams et al., 2005; Plant and Robertson, 2008).

Vector Transmission (Biotic)

Fruits are consumed and the seeds are spread by blackbirds in New Zealand (Williams et al., 2005).

Intentional Introduction

The species has been introduced to many temperate areas of the world as a garden ornamental (e.g. Williams et al., 2005).

Pathway Causes

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CauseNotesLong DistanceLocalReferences
Horticulture Yes Yes Williams et al., 2005
Internet salesSites selling the species can be found by an internet search Yes
Nursery tradeNurseries selling the species in UK can be found by an internet search. Available in nurseries in Au Yes Plant and Robertson, 2008

Impact Summary

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CategoryImpact
Cultural/amenity Negative
Environment (generally) Negative

Economic Impact

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G. tinctoria is an environmental weed so its economic impact is largely through the cost of control measures rather than a reduction of agricultural or forest productivity. However there are sites in Ireland where the species has invaded native species-rich native grassland, (Hickey and Osborne, 1998), which reduces the value of the land for grazing. National or regional governments and hence taxpayers in, for example, Ireland, UK, the Azores, Australia and New Zealand have to bear the cost of regulation, raising public awareness and of control measures.

In New Zealand there is concern that G. tinctoria can block drains and streams (Weedbusters, 2003).

Environmental Impact

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Impact on Habitats 

In Ireland the invasion processes profoundly affected the structure of invaded seed bank communities. G. tinctoria formed an enormous persistent seed bank, with an average of 60,428 ± 47,131 (mean ± SD) seedlings m-2 (Gioria and Osborne, 2007). At invaded sites, Hickey and Osborne (1998) noted changes in nitrogen mineralisation, but did not consider that these were directly associated with the changes in species composition, because a high proportion of the nitrogen is actually immobilised above ground in the rhizomes of the plant. There are a number of examples of where G. tinctoria has invaded national parks and areas of high conservation value including Achill Island, County Mayo, Ireland and various locations on the west coast of New Zealand, e.g. Egmont Ecological District (Williams et al., 2005).

Impact on Biodiversity 

Gunnera reduces the biodiversity value of infested sites. It can lead to the local extinction of some species with the formation of almost monospecific stands of Gunnera. Where it has become the dominant species in marshland in Ireland, plants have actively changed the process of vegetation succession, replacing grey willow (Salix cinerea), (Hickey and Osborne, 1998). In New Zealand G. tinctoria has a high impact due to it shading out rare and endangered indigenous flora and fauna on moist coastal cliffs. The huge leaves of each G. tinctoria mean it can impact on a disproportionately large number of the comparatively small, native coastal herbs. Law (2003) lists the following native plants that are threatened in Tarabaki: Coprosma acerosa (the ’unnamed‘ Taranaki coastal variety, also known as tarakupenga, tataraheke, or sand coprosma), Euphorbia glauca (waiu-atua, waiu-o-Kahukura), Myositis pygmaea var. pygmaea, Sonchus kirkii, coastal buttercups Ranunculus repens and R. acaulis, Mentha cunninghamii, Oreomyrrhis ‘minutiflora’, Hebe elliptica (shore koromiko), a rare Craspedia (button daisy), and Pimelea prostrata var urvilleana (pinatoro, wharengarara); melea prostrata var urvilleana which is the plant food for caterpillars of the endemic daytime-flying moth; Notoreas ‘Taranaki’, which is found only in South Taranaki and Northwest Nelson.

Social Impact

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Invasion of coastal cliffs in New Zealand has led to a change in the appearance of the landscape (e.g. in areas of high importance to tourism such as Taranaki. The species has been reported here to obstruct access to natural and recreational areas (Weedbusters, 2003).

Risk and Impact Factors

Top of page Invasiveness
  • Proved invasive outside its native range
  • Abundant in its native range
  • Tolerant of shade
  • Benefits from human association (i.e. it is a human commensal)
  • Long lived
  • Fast growing
  • Has high reproductive potential
  • Has propagules that can remain viable for more than one year
  • Reproduces asexually
Impact outcomes
  • Damaged ecosystem services
  • Ecosystem change/ habitat alteration
  • Infrastructure damage
  • Modification of successional patterns
  • Monoculture formation
  • Reduced amenity values
  • Reduced native biodiversity
  • Threat to/ loss of endangered species
  • Threat to/ loss of native species
Impact mechanisms
  • Competition - monopolizing resources
  • Competition - shading
  • Competition - smothering
  • Rapid growth
Likelihood of entry/control
  • Highly likely to be transported internationally deliberately

Uses List

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Environmental

  • Ornamental

Materials

  • Dye/tanning

Ornamental

  • Propagation material

Similarities to Other Species/Conditions

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G. tinctoria may easily be confused with G. manicata Linden ex André, a closely related species in the sub-genus Panke from Brazil that is also widely cultivated. This is also a large leaved species.

This south Brazilian species can grow even taller than its Chilean relation but it looks very similar and is often mistaken for it. According to Sykes (1969) there are a number of characters that can be used to distinguish between the two. The rhizome of G. manicata is thicker and more massive. A better distinguishing character is the large laciniate or jaggedly cut scales at the base of the leaves and inflorescence. In G. manicata there is a prominent development of membranous ’webbing‘ between the main lobes of the scale whereas in G. tinctoria this is not well developed and so the lobes are often almost free to the main rachis of the scale. The lengths and thickness of the inflorescence branches are also diagnostic. The diameter of central part of main inflorescence axis is 3.0 to 3.3 cm in G. manicata but 4 to 4.5 cm in G. tinctoria. Length of typical inflorescence branches from about half way up the main axis is 9.5-11 cm compared to 5-7 cm, while the diameter of central part of the typical middle inflorescence branches ranges from 3-4 cm and from 5-7 cm in the two species, respectively.

Although G. manicata is not generally considered to be invasive there are indications that it may naturalise in New Zealand. Webb et al. (1988) did not record it as naturalised in New Zealand but Williams et al. (2005) report observations from the early 2000s of seedlings near Wanganui while a few G. manicata seedlings have been found near planted specimens by Pigeon Bay domain, Banks Peninsula. This has led Williams et al. (2005) to suggest that all large-leaved Gunnera species should be banned from propagation and sale in New Zealand.

Prevention and Control

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Prevention

Measures are in place in Ireland and New Zealand and are being considered in UK to prohibit the sale and planting of G. tinctoria as an ornamental (see detailed discussion under Risk of Introduction). Public awareness campaigns through production of fact sheets and articles in the media are key tools in preventing further planting of the species e.g. a Victorian Alert Weed Fact Sheet in Australia (Plant and Robertson, 2008), fact sheets in various districts of New Zealand (Timmins and Blood, 2003; Horizons, 2006).

Eradication

As G. tinctoria has ’unwanted organism‘ status under the New Zealand biosecurity law, councils and land-owners have an obligation to undertake eradication where possible. Such programmes are included in regional Pest Plant Management Strategies (RPMS) developed by regional councils. A typical example has been described by Law (2003) for Taranaki and includes mechanical removal of plants and application of herbicides, particularly on coastal cliffs. The Taranaki RPMS lists the species as a ‘containment pest plant’. This recognises that it is already locally abundant but aims to prevent its spread to new areas in the region and, where practicable, to reduce existing infestations. From July 2003, land occupiers have been required to destroy all adult and juvenile plants on their land. Two other regional councils (Environment Waikato and Greater Wellington) specify its control at sites of ecological value, and two more (Horizons Regional Council and Bay of Plenty) have opted for regional surveillance status (Williams et al., 2005).

Control 

Physical/mechanical control

As the seed of G. tinctoria has little dormancy the first action should be to remove flowering spikes from any plants. In New Zealand this has been found to reduce re-infestation from the seed bank after two years (Williams et al., 2005). Follow-up monitoring and further cutting back of plants will be needed. Where mechanical removal is used it is important to uproot the rhizome.

Movement control

Legal restrictions on sale of G. tinctoria are in place in Ireland and New Zealand (see section on Risk of introduction for further details). Plant and Robertson (2008) argue that similar restrictions should be introduced in Australia.

Chemical control

Use of herbicides is recommended in New Zealand, particularly in areas where access for mechanical control operations is difficult and potentially dangerous, such as on unstable wet cliffs. Horizons District Council recommends applying a broadcast application of triclopyr 600 EC with organo-silicone spreader, or metsulfuron-methyl (Horizons, 2006).

Law (2003) reported that Taranaki Regional Council found use of picloram to be a useful treatment. A 1.5-2% solution of glyphosate with a suitable wetter has also been applied by knapsack sprayer. On steep cliffs, abseilers cut the leaves off plants and immediately treat the cut surface with 25% glyphosate. The growing tips are not cut off to avoid them dropping and re-growing. Results to date have been promising; however, some native seedlings have come up in the cleared areas and there was some re-growth on about 4.5% of the treated G. tinctoria plants. After spraying, some rhizomes take up to 18 months to rot.

Control by utilization

Williams et al., (2005) have observed that leaves of G. tinctoria are browsed by cattle and noted a lack of seedlings in pasture - despite the many large plants adjacent and the consequent seed rain. This suggests that grazing will restrict encroachment of the weed in to pasture.

References

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Alien Plants in Ireland, 2008. Database of alien plants in Ireland. http://www.biochange.ie/alienplants/

Bergman B; Osborne B, 2002. The Gunnera-Nostoc symbiosois. Biology and Environment. Proceedings of the Royal Irish Academy, 102B(1):35-39.

Calflora, 2008. Gunnera tinctoria Taxon report 3976. Web site of the Calflora Database. http://www.calflora.org

Dawson MI, 1983. Chromosome numbers of three South American species of Gunnera (Gunneraceae). New Zealand Journal of Botany, 21(4):457-459.

EPPO, 2014. PQR database. Paris, France: European and Mediterranean Plant Protection Organization. http://www.eppo.int/DATABASES/pqr/pqr.htm

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26/06/08 Original text by:

Charlie Riches, Consultant, UK

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