Rhamnus cathartica (buckthorn)
- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Plant Type
- Distribution Table
- History of Introduction and Spread
- Risk of Introduction
- Habitat List
- Hosts/Species Affected
- Host Plants and Other Plants Affected
- Growth Stages
- Biology and Ecology
- Latitude/Altitude Ranges
- Air Temperature
- Rainfall Regime
- Soil Tolerances
- Natural enemies
- Notes on Natural Enemies
- Means of Movement and Dispersal
- Plant Trade
- Impact Summary
- Environmental Impact
- Impact: Biodiversity
- Threatened Species
- Social Impact
- Risk and Impact Factors
- Uses List
- Similarities to Other Species/Conditions
- Prevention and Control
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Rhamnus cathartica L.
Preferred Common Name
Other Scientific Names
- Cervispina cathartica (L.) Moench
- Rhamnus catharticus L.
International Common Names
- English: Christ's thorn; common buckthorn; European buckthorn; french berries; hart's-thorn; purging buckthorn; purging buckthorn; rainberry-thorn; Rhineberry thorn; waythorn; yellow berry
- Spanish: cambrón
- French: nerprun purgatif
- Russian: harilik türnpuu; kitseuipuu; türnapuu; viherpuu; vihur
Local Common Names
- Argentina: cambronera; espino cerval; uva cabruna
- Croatia: pasdrijen; pasjakovina; prava krkavina
- Czech Republic: resetlák pocistivy
- Denmark: korsved; vrietorn
- Finland: orapaatsama
- France: bourge; cathartique; epine de cerf; epine noire; noirprun
- Germany: Amselbeeren; Echter Kreuzdorn; Echter Purgierkreuzdorn; Färbebaum; Feldbeerbaum; Gelbbeeren; Gemeiner Kreuzdorn; Hexendorn; Hirschdorn; Kreuzdorn; Purgier; Purgier- Kreuzdorn; Stechdorn; Wegdorn
- Italy: ramno catartico; spina cervino; spina santa; spincervino; spino di Christo; spino gervino; spino merlo
- Netherlands: wegedoorn; wegedoorn soort
- Norway: geitved
- Spain: carrasquilla; espino cerval; espino hediondo; sanguinaria menor
- Sweden: getapel; vägtorn
- RHACT (Rhamnus catharticus)
Summary of InvasivenessTop of page
R. cathartica was introduced to North America from Europe more than 100 years ago and it has continued to spread into new areas across the continent. Although it has been declared a noxious weed in some US states, it is still described in horticultural literature and may be spread as an ornamental. Once established it maintains itself due to prolific seed production, vigorous growth over an extended growing season, and its ability to regenerate following burning and cutting. These characteristics make it difficult to eradicate. The repeated applications of herbicide needed to eliminate R. cathartica are laborious and expensive. Consequently, most restoration work has been conducted in natural ecosystems of special interest. The adverse effect of R. cathartica on native species arises because it shades out understorey plants, or because of its purported allelopathic effect on seedlings.
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Plantae
- Phylum: Spermatophyta
- Subphylum: Angiospermae
- Class: Dicotyledonae
- Order: Rhamnales
- Family: Rhamnaceae
- Genus: Rhamnus
- Species: Rhamnus cathartica
Notes on Taxonomy and NomenclatureTop of page
Although R. cathartica is the preferred name for the species, it is widely reported as R. catharticus; both forms are attributed to Linneaus. 'Rhamnus' refers to the Greek word for 'thorn', and the small thorns borne at the tips of most branches help to distinguish this species. The specific name 'cathartica' refers to the medicinal qualities of the plant, which has been used since Medieval times as a potent laxative and in other herbal remedies to treat ailments such as jaundice, gout and arthritis. An alternative name occasionally seen in the literature is Cervispina cathartica; this too alludes to the thorns that the plant bears and to its purgative effects. A close relative, R. purshiana, is the source of cascara. The German name 'Kreuzdorn' refers to the branches that arise in pairs almost at right angles to the main stem; this cross-like form was thought to protect against evil.
DescriptionTop of page
R. cathartica is a deciduous, profusely-branched shrub or small tree that typically grows to heights of 2-8 m with an irregular spreading crown supported by opposite, lateral branchlets which form at right angles to the main branches (Polunin, 1969). Bark is dark grey to brownish in colour becoming rough and scaly at maturity. The twigs have prominent lenticels. Branchlets are generally smooth and glabrous, but shorter shoots may develop a rough, warty appearance due to closely-spaced leaf scars. Twigs are normally tipped with a conspicuous single spine 0.5-5.0 cm in length; a sharp stout spine is also present in many of the branch forks. The simple, deciduous leaves are dull green in colour, 3-7 cm in length and more than half as wide, strongly glabrous or finely pubescent, and finely serrate. Leaves are short-stalked, mostly opposite or sub-opposite with ovate to elliptical blades which are 2-2.5 times as long as the petiole (Tutin et al., 1968). Leaf tips are obtuse or cuspidate and may develop a small curved fold. The blades have 3-5 curved veins which tend to be more conspicuous on the lower surface. Leaves remain on the plant until late in the autumn which greatly assists identification and can provide a conspicuous clue to density. R. cathartica is normally dioecious with 4-merous male and female flowers borne on separate plants. Flower clusters arise form the older branches. The flowers are greenish-yellow in colour, about 4 mm across and bear 4 sepals and petals. The sepals are about 2 mm long; the petals are erect, lanceolate and 1-1.3 mm in length in staminate flowers and about 0.6 mm long in pistillate flowers (Gleason, 1963). The ripe fruits develop as globular drupes 6-10 mm in diameter which change from green to black as they mature. Each drupe contains 3-4 stones (pyrenes) which are obovoid with a quadrant or triangular cross-section. Seed size is reported as 42/g (Young and Young, 1992). Germination is epigeal with 2 heart-shaped cotyledons (Godwin, 1943).
Plant TypeTop of page Broadleaved
DistributionTop of page
R. cathartica is found throughout Europe except Iceland and Turkey (Polunin, 1969) and extends into western Asia. The northern limit of its distribution is approximately 62°N in Scandinavia. Although R. cathartica is absent from southern parts of Europe, and is not reported on islands such as Sardinia, Corsica and the Balearics, it grows as far south as Morocco and Algeria where it is restricted to higher altitudes (Godwin, 1943). R. cathartica is widespread in north central and northeastern parts of North America, being found at varying densities across Canada from Nova Scotia to Alberta, south to Utah and east to Virginia in the USA with some individuals reported from California (USDA-NRCS, 2002). In Canada it is very common in southern Ontario, although its distribution is interrupted by the Canadian Shield. It occurs less widely in Quebec and the Maritime provinces and sporadically across the prairies. The most westerly occurrence in Canada is in Alberta where it is found in coulees as a rare escape from cultivation (Moss, 1983). R. cathartica has also been reported from Buenos Aires province in Argentina (Anon., 2003).
Distribution TableTop of page
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/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Planted||Reference||Notes|
|Afghanistan||Present||Native||Natural||Tutin et al., 1968|
|Canada||Present||Present based on regional distribution.|
|-New Brunswick||Present||Introduced||Invasive||Planted||Maw, 1984|
|-Nova Scotia||Present||Introduced||Invasive||Planted||Maw, 1984|
|-Prince Edward Island||Present||Introduced||Invasive||Planted||Maw, 1984|
|USA||Present||Present based on regional distribution.|
|-New Hampshire||Present||Introduced||Invasive||Planted||USDA-NRCS, 2002|
|-New Jersey||Present||Introduced||Invasive||Planted||USDA-NRCS, 2002|
|-New York||Present||Introduced||Invasive||Planted||USDA-NRCS, 2002|
|-North Dakota||Present||Introduced||Invasive||Planted||USDA-NRCS, 2002|
|-Rhode Island||Present||Introduced||Invasive||Planted||USDA-NRCS, 2002|
|-South Carolina||Present||Introduced||Invasive||Planted||USDA-NRCS, 2002|
|-South Dakota||Present||Introduced||Invasive||Planted||USDA-NRCS, 2002|
|Albania||Present||Native||Natural||Tutin et al., 1968|
|Austria||Present||Native||Natural||Tutin et al., 1968|
|Belgium||Present||Native||Natural||Tutin et al., 1968|
|Bosnia-Hercegovina||Present||Native||Natural||Tutin et al., 1968|
|Bulgaria||Present||Native||Natural||Tutin et al., 1968|
|Czechoslovakia (former)||Present||Native||Natural||Tutin et al., 1968|
|Denmark||Present||Native||Natural||Tutin et al., 1968|
|Estonia||Present||Native||Natural||Tutin et al., 1968|
|Finland||Present||Native||Natural||Tutin et al., 1968|
|France||Present||Native||Natural||Tutin et al., 1968|
|Germany||Present||Native||Natural||Tutin et al., 1968|
|Greece||Present||Native||Natural||Tutin et al., 1968|
|Hungary||Present||Native||Natural||Tutin et al., 1968|
|Ireland||Present||Native||Natural||Tutin et al., 1968|
|Italy||Present||Native||Natural||Tutin et al., 1968|
|Netherlands||Present||Native||Natural||Tutin et al., 1968|
|Norway||Present||Native||Natural||Tutin et al., 1968|
|Poland||Present||Native||Natural||Tutin et al., 1968|
|Portugal||Present||Native||Natural||Tutin et al., 1968|
|Romania||Present||Native||Natural||Tutin et al., 1968|
|-Central Russia||Present||Native||Natural||Tutin et al., 1968|
|-Northern Russia||Present||Native||Natural||Tutin et al., 1968|
|-Southern Russia||Present||Native||Natural||Tutin et al., 1968|
|-Western Siberia||Present||Native||Natural||Tutin et al., 1968|
|Serbia||Present||Native||Natural||Tutin et al., 1968|
|Spain||Present||Native||Natural||Tutin et al., 1968|
|Sweden||Present||Native||Natural||Tutin et al., 1968|
|Switzerland||Present||Native||Natural||Tutin et al., 1968|
|UK||Present||Native||Natural||Tutin et al., 1968|
|Ukraine||Present||Native||Natural||Tutin et al., 1968|
|Yugoslavia (former)||Present||Native||Natural||Tutin et al., 1968|
History of Introduction and SpreadTop of page
R. cathartica was introduced to North America from Europe as an ornamental, possibly before 1800 (Wyman, 1971), and appeared in taxonomic collections by the 1880s (Wolf, 1938). By the 1900s it had become naturalized and widespread in northeastern USA where it was used as a hedge and shelterbelt shrub, as an ornamental in parks and gardens, and for wildlife habitat. Some plantings may have been established because of the medicinal value of the fruits. Herbarium specimens document its presence in Michigan from 1914 (Gil-ad and Reznicek, 1997). The first record in Wyoming is 1979; at the time it was 504 km from the nearest known naturalized population located in South Dakota (Lichvar, 1980). R. cathartica was not recorded in Canada until the late 1890s, first in Ontario and thereafter in Quebec and the Atlantic provinces. It was introduced to Saskatchewan in the 1930s as a potential shelterbelt shrub with initial trials conducted at the Dominion Tree Nursery in Sutherland, now a suburb of Saskatoon. Experiments were terminated once it was realized that buckthorn was an alternate host to oat crown rust (Puccinia coronata var. avenae), but not before the species had escaped from cultivation (Archibold et al., 1997). R. cathartica has been declared a noxious weed in some states and is no longer sold by nurseries in Iowa and Minnesota. However, it continues to be spread by birds and other natural agents.
Risk of IntroductionTop of page
R. cathartica is still listed in horticultural catalogues, although its invasiveness is usually noted. Since January 2002, the USA requires seeds of all species to have phytosanitary certificates, so this has limited importation from overseas suppliers.
HabitatTop of page
R. cathartica is native to Europe and Asia where it is found locally in the understorey of woodlands, in scrub and in wet alkaline fens. In the UK it is associated with oak, beech and ash woods on base-rich soils (Godwin, 1943). It grows vigorously in open areas, such as pastures (Polunin, 1969), and forms thickets on exposed rocky slopes (Hinneri, 1972). In northern Europe and western Asia it grows in mixedwood forests and in stands of pine.
R. cathartica has become naturalized in many parts of eastern and central North America. In eastern North America it grows in the light shade of deciduous woodlands. It is especially common in stands of oak, and often establishes in deadfall openings; fence rows, roadsides, ravines and river banks also provide a suitable habitat (Maw, 1984). In New England, characteristic habitats include abandoned fields, early successional forests, disturbed forest edges, floodplain forests, open disturbed areas, pastures, planted forests, roadsides and vacant lots (IPANE, 2001). In the Great Plains it readily invades native shrub communities where light is not a limiting factor. In Saskatchewan it is reported from riparian woodlands and aspen groves where it thrives in the open canopy of the trees, and has become the dominant understorey plant at some sites (Archibold et al., 1997). In Manitoba, Maw (1984) reported that it was found mainly in parks and gardens in urban areas.
Habitat ListTop of page
|Terrestrial – Managed||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-natural||Natural 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)|
Hosts/Species AffectedTop of page
Degradation of natural areas due to the establishment of dense, even-aged stands of R. cathartica is of primary concern to conservation authorities (USGS, 2000). R. cathartica leafs out early and retains its leaves late into the autumn thereby shading out smaller plants. In Wisconsin (USA), R. cathartica remains in leaf for an average of 58 days longer than comparable native shrubs such as Cornus racemosa and Prunus serotina; approximately 35% of the annual carbon gain for R. cathartica occurs before leaf emergence in C. racemosa (Harrington et al., 1989). Seedling establishment of native species under the canopy is also limited. Reduced recruitment of native tree species has been noted in the deciduous forests of eastern North America as well as crowding out of herbaceous understorey species, such as Thalictrum dioicum, Trillium grandiflorum, Maianthemum canadense and Trientalis borealis (Gale, 2001). The absence of seedling emergence from soil samples collected from dense stands of R. cathartica (Archibold et al., 1997), and the reappearance of native and exotic species in sites from which R. cathartica had been removed, suggests that the species may be allelopathic (Boudreau and Willson, 1992). However, little evidence of allelopathy was noted in subsequent laboratory experiments using aqueous extracts from leaf litter and roots (Archibold et al., 1997).
R. cathartica is also a threat to agriculture because it is the alternate host of crown rust of oats, Puccinia coronata var. avenae. Crown rust adversely affects yield, weight and protein content of oat seed (Peturson, 1954). The spermagonial and aecial stages of the fungus occur on R. cathartica leaves, which may favour pathogenic variation because of hybridization (Simons et al., 1979; Oard and Simons, 1983). Infections of crown rust from R. cathartica are usually very local, but can lead to complete crop loss; infection levels usually decline linearly with distance from infected R. cathartica and are negligible beyond a few hundred metres (Harder, 1975). Crown rust can also infect several cool season turfgrasses and native grasses (Partridge, 1998).
Recent occurrences of the soyabean aphid (Aphis glycines) in Illinois, Minnesota, Wisconsin and other central US states have been associated with R. cathartica and R. davurica, another exotic species. Winter survival is by overwintering eggs on these species of Rhamnus (North Central Pest Management Centre, 2003).
Host Plants and Other Plants AffectedTop of page
Growth StagesTop of page Seedling stage, Vegetative growing stage
Biology and EcologyTop of page
The chromosome number is 2n = 24 (Tutin et al., 1968). Preliminary evidence for hybridization between R. cathartica and R. utilis has been reported at a site in Michigan (Gil-ad and Reznicek, 1997); both species were introduced from Eurasia.
Physiology and Phenology
Studies in Wisconsin, USA (Harrington et al., 1989) showed that leaf emergence in R. cathartica in open habitat occurred in late April compared with early April for plants growing in the understorey of a mature closed-canopy hardwood forest composed of Quercus rubra, Carya ovata and Acer saccharum. Leaves were retained in both sites until mid-November. Specific leaf mass ranged from 4.17 to 10.47 mg/cm² in open-grown shrubs compared with 2.13-3.50 mg/cm² for understorey plants. Foliar nitrogen content was 1.77 gN/m² in the open-grown plants compared with 0.83 gN/m² in the forest shrubs. For P, Ca and Mg, foliar nutrient levels were similar in both populations, but K levels were about twice as high in the understorey plants as in the open-grown specimens. Seasonal maximum photosynthesis rates dropped from 12.80 µmol carbon dioxide/m²/s for open-grown plants to 6.18 µmol carbon dioxide/m²/s for individuals in the understorey. For understorey plants, rates were highest in the spring due to greater light availability before the overstorey leafed out, and increased in the autumn as the trees senesced. R. cathartica continued to photosynthesize until late autumn, and retained its leaves for about 3 weeks longer than native shrubs. Leaf longevity may account for the success of this exotic shrub.
Natural reproduction in R. cathartica is sexual. However, the species sprouts vigorously from cut or damaged stems which may account for occasional references to asexual means (Converse, 1984; Gale, 2001). R. cathartica produces seed at an early age (Godwin, 1943). The species is normally dioecious. Vestigial stamens are present in the female flowers, and occasional polygamous flowers have been reported (Converse, 1984). The population of males and females varies locally. Godwin (1943) reported a ratio of 7 female to 1 male at some sites in England, while equal numbers of males and females were reported elsewhere.
Flowering begins in late spring (Fernald, 1987) with an average date of 4th June noted for southern England (Godwin, 1943). Flowering occurs concurrently with leaf expansion (Hubbard, 1974). Pollination is by insects; bumble bees and hoverflies have been observed visiting flowers in Germany and the UK. Fruit production is prolific with 1455 fruits reported on a bush 2.1 m high in the UK, although this may decrease in plants growing in exposed places (Godwin, 1943). Fruits mature during July-November in the USA (Hubbard, 1974). Premature dispersal is minimized by the presence of anthraquinones in the immature fruit (Trial and Dimond, 1979) and, because of their persistence, the mature fruits are generally consumed only after other food sources have been depleted. The fruits are mainly dispersed by birds, from September to April in New York State (Gill and Marks, 1991).
Seeds remain viable for at least 2 years, exhibit high germination rates, and germinate equally well in darkness or light (Godwin, 1943), although seedling recruitment is most successful under ample light and declines as shade increases (Converse, 1984). Young and Young (1992) noted that germination occurs at temperatures of 20-30°C under an 8-hour photoperiod following a 2- to 4-week period of pre-chilling at 1-5°C. Seed germination is facilitated by removal from the fruit and scarification (Gourley and Howell, 1984). A period of cold stratification may be required to break dormancy. Archibold et al. (1997) noted that no seedlings emerged from intact fruits. Seedling emergence for seeds extracted from the fruits commenced after 25 days; peak emergence occurred after 34-40 days, with a mean time to emergence of 42 days. Mean emergence rate was 88%. Additional experiments suggested that prolonged immersion in water may be detrimental to seed germination; a 10% reduction in emergence was noted in seeds that were immersed for 2 weeks, and no germination occurred in seeds that were immersed for 2 months. Although the fruits of R. cathartica can float for 6 days and seeds are buoyant for 3 days (Ridley, 1930), this is unlikely to benefit dispersal, except perhaps in occasionally flooded riparian habitats.
Gill and Marks (1991) described several mechanisms which affect emergence and establishment of seedlings in recently abandoned agricultural land in New York State, USA. Seeds deposited in open sites were not consumed, whereas 100% predation was noted beneath a cover of herbs, probably due to deer mice (Peromyscus spp.). In other experiments, average seedling emergence was about 20% in bare soil and under herbaceous cover, and no significant difference was noted between moderately well-drained sites and less well-drained sites. Seedling losses were about five times greater under herbs than in open sites and this was mainly attributed to predation. Frost heaving also contributed to seedling loss, especially in open sites. Significantly higher biomass was noted at 5 months and 17 months for seedlings grown in open sites. Gill and Marks (1991) concluded that the probability of establishment of R. cathartica in old fields was very low. However, land use history may also play a role, since R. cathartica is more likely to invade abandoned pastures than abandoned cropland (Stover and Marks, 1998).
The widespread occurrence of R. cathartica in North America is attributed to the similarity between its naturalized and indigenous habitats. In addition, adult plants have large, shading leaves which modify understorey microhabitats to the detriment of native species. Disturbance of natural communities through drainage, fire, woodland grazing and cutting may also have facilitated spread (Converse, 1984).
R. cathartica acts as a host for the soyabean aphid (Aphis glycines) which has the potential to become a serious problem in some parts of North America. In addition, R. cathartica is associated with oat crown rust (Puccinia coronata var. avenae). With these exceptions the species appears to have little direct impact on agriculture. The main concern relates to its ability to invade many types of natural habitats. Once established in the understorey it outcompetes many native species. Biodiversity is greatly reduced where dense thickets develop, and the potential for the re-establishment of native species is limited.
Latitude/Altitude RangesTop of page
|Latitude North (°N)||Latitude South (°S)||Altitude Lower (m)||Altitude Upper (m)|
Air TemperatureTop of page
|Parameter||Lower limit||Upper limit|
|Absolute minimum temperature (ºC)||-45||0|
|Mean annual temperature (ºC)||2||14|
|Mean maximum temperature of hottest month (ºC)||15||25|
|Mean minimum temperature of coldest month (ºC)||-18||10|
RainfallTop of page
|Parameter||Lower limit||Upper limit||Description|
|Dry season duration||0||9||number of consecutive months with <40 mm rainfall|
|Mean annual rainfall||300||1200||mm; lower/upper limits|
Rainfall RegimeTop of page Summer
Soil TolerancesTop of page
Natural enemiesTop of page
|Natural enemy||Type||Life stages||Specificity||References||Biological control in||Biological control on|
|Aceria rhamni||Herbivore||Whole plant|
|Sorhagenia janiszewskae||Herbivore||Growing point|
|Tetra rhamni||Herbivore||Whole plant|
|Trichochermes walkeri||Herbivore||Whole plant|
|Trioza rhamni||Herbivore||Whole plant|
Notes on Natural EnemiesTop of page
Studies funded by Minnesota State Department of Agriculture in association with CABI Bioscience have identified more than 200 species of arthropods and 40 species of fungi that are associated with buckthorns in Eurasia, of which approximately 18 and 14, respectively, are likely to be restricted in host range to the genera Rhamnus and Frangula. About a dozen species of potential arthropod biological control agents have been identified for further study; these include Gonepteryx rhamni, Oberea pedemontana, Psylla rhamnicola [Cacopsylla rhamnicola], Trichochermes walkeri and Trioza rhamni. Similarly, several species of fungi are identified as having potential as biological control agents, and host-specificity studies are continuing (Gassmann, 2002). Potential biocontrol agents are discussed in more detail in the section on Biological Control.
A lethal witches' broom disease related to the apple proliferation (AP) phytoplasma cluster has been identified in southwestern Germany. The leaves of infected plants appear deformed and their vigour steadily decreases. Severely infected plants do not bear fruit. These specimens also exhibited browning of the phloem. Phloem necrosis caused by reduced hardiness of phytoplasma-infected plants resulted in tissue death during the winter (Maurer and Seemüller, 1996).
Means of Movement and DispersalTop of page
Natural Dispersal (Non-Biotic)
Natural dispersal is minimal. Many fruits fall directly beneath the parent shrubs resulting in high seed and seedling densities under mature female plants. A fruit fall rate of 28/m² was reported beneath large R. cathartica shrubs in Saskatchewan, Canada, with an additional 19 seeds/m² collected in seed traps. Seedling emergence at a rate of 620/m² was noted from soil cores taken beneath a dense buckthorn stand to a depth of 10 cm; mean emergence time for these seedlings was 28 days (Archibold et al., 1997). Very occasionally, dispersal may be effected by water.
Vector Transmission (Biotic)
Dispersal is principally by birds, such as thrushes (Turdus sp.), waxwings (Bombycilla sp.), starlings (Sturnus vulgaris), and jays (Garrulus sp.) (Godwin, 1943; Archibold et al., 1997); small mammals, including voles and mice, may also act as vectors (Converse, 1984; USGS, 2000). The chemical content of the fruits may influence seed dispersal. Those that are consumed are generally expelled quickly and redistributed with little damage. Seedlings of R. cathartica typically appear along fencerows, beneath perch trees and at the edge of woods, and the invasiveness of the species is greatly enhanced by avian dispersal (Gale, 2001).
The use of R. cathartica as a hedgerow plant would have assisted dispersion in the past, but further movement cannot be attributed to current agricultural practices.
No documented instances.
R. cathartica has been used extensively as an ornamental shrub. Some demand for R. cathartica may also be expected because of its use as a herbal remedy.
Plant TradeTop of page
|Plant parts not known to carry the pest in trade/transport|
|Fruits (inc. pods)|
|Growing medium accompanying plants|
|Stems (above ground)/Shoots/Trunks/Branches|
|True seeds (inc. grain)|
Impact SummaryTop of page
|Fisheries / aquaculture||None|
ImpactTop of page
At present the economic impact of R. cathartica is comparatively small despite it being an alternate host for oat crown rust (Puccinia coronata var. avenae) and the soyabean aphid (Aphis glycines). However, considerable time and expense have been invested to remove the shrub from invaded habitats.
Environmental ImpactTop of page
R. cathartica readily invades native woodland, prairie and riparian communities and once established outcompetes local species. Conservation authorities throughout North America have initiated significant campaigns to eradicate the shrub. Heneghan et al. (2002) reported that leaf litter decomposition occurred more rapidly for R. cathartica than for associated tree and shrub species in Illinois. This was attributed to the high nitrogen content of the litter. Rapid litter decomposition may increase soil fertility and favour the growth of R. cathartica, although ultimately, it may limit soil fauna diversity.
Impact: BiodiversityTop of page
Apart from a significant reduction in density and diversity of plant species in sites where R. cathartica has become established, the species can also affect bird populations. American robins (Turdus migratorius) and wood thrush (Hylocichla mustelina) have been observed to nest in R. cathartica; this made their nests more accessible to predators and increased their mortality compared with individuals nesting in native shrubs (Schmidt and Whelan, 1999).
Threatened SpeciesTop of page
|Threatened Species||Conservation Status||Where Threatened||Mechanism||References||Notes|
|Asplenium scolopendrium var. americanum (American hart's-tongue fern)||No Details||New York||Competition - monopolizing resources||US Fish and Wildlife Service, 2012|
Social ImpactTop of page
No direct social impacts have been reported, except that the presence of R. cathartica can visually detract from local vistas. Local access to sites may be impeded where dense stands have developed.
Risk and Impact FactorsTop 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
- Damaged ecosystem services
- Ecosystem change/ habitat alteration
- Negatively impacts tourism
- Reduced amenity values
- Reduced native biodiversity
- Competition - monopolizing resources
- Pest and disease transmission
- Produces spines, thorns or burrs
- Highly likely to be transported internationally deliberately
- Difficult/costly to control
UsesTop of page
R. cathartica has been used extensively as a hedgerow and ornamental plant. It has long been used in the treatment of various ailments because of its diuretic and emetic properties. The berries have also been used as a dye for various purposes. Unripe berries yield a yellow dye, berries picked when they are black make a green dye, and purple dye can be extracted from berries that are harvested later in the winter.
Uses ListTop of page
- Host of pest
- Poisonous to mammals
Similarities to Other Species/ConditionsTop of page
Several species of shrub are similar in appearance to R. cathartica. Frangula alnus is distinguished mainly through habitat preference, being found in wetter, less shaded and more acidic soils than R. cathartica (Tansley, 1968). In Europe, other related species, such as R. alaternus, R. persicifolius and R. saxatilis, bear lanceolate leaves or are smaller than R. cathartica. Similarly, several native species of buckthorn occur in North America; the most common include R. alnifolia, R. caroliniana and R. lanceolata; generally they are distinguished by the absence of spines and by differences in leaf shape. Frangula alnus is also naturalized in North America, but habitat preference, absence of spines and entire leaf margins help separate this species from R. cathartica. In the drier prairie regions of North America, R. cathartica may be confused with Prunus virginiana, because of similar fruits and leaves, although P. virginiana does not have spines. A superficial resemblance to Betula occidentalis and Elaeagnus commutata has been reported by some conservation crews working in riparian woodlands during leafless periods.
Prevention and ControlTop of page
The combination of heavy fruit production and high germination rates allows R. cathartica to rapidly dominate an understorey. Its prolific nature makes it difficult to eradicate. Various methods can be used, and repeated treatments may be required to kill mature plants. The capacity of extended seed dormancy also necessitates repetition. Because the species is dioecious, eradication effort is more effective if directed against the female, seed-bearing plants.
Fire is effective in killing R. cathartica seedlings and can top-kill mature shrubs. Some plants may be killed in one treatment, but the species resprouts vigorously and burning may need to be repeated annually or biennially over several years before it is eradicated. Burning is the preferred method in communities which are adapted to fire, but should not be used if the natural community will be affected adversely (Heidorn, 1991). In Saskatchewan, Canada, it was noted that new shoots re-emerged in the spring in plants that were cut and subsequently burned. The new crowns were denser and the leaves larger than on untreated individuals in the same stand (Archibold et al., 1997). For seedlings, burning is recommended during the growing season in the year after the mature plants have been killed. Because R. cathartica leafs out earlier than most native species, typically it is top-killed by burning in late April or early May. Carbohydrate levels are low in roots at this time, and resprouting vigour may be reduced (Converse, 1984). Stands comprised of fire-tolerant native species are best suited to restoration by controlled burns. One difficulty is that R. cathartica often shades out understorey plants; this reduces leaf litter and cured fuel loads which can limit the spread and intensity of the fire (Gale, 2001). Burned areas may also be more readily invaded by seedlings than sites with established ground cover. Underplanting of restored woodlands with native woody species has been used to reduce re-invasion of R. cathartica in some locations (Scriver and Leach, 1998).
Cutting shrubs does not usually kill them; new shoots develop from the stump, and the treatment must be repeated over several seasons, preferably twice a year for two or three consecutive years (The Nature Conservancy, 2001). Similarly, girdling can weaken the shrubs, but new sprouts must be removed as they develop. For girdling to be effective all bark must be removed from 10-15 cm of the stem (Heidorn, 1991). Seedlings up to 1 m in height can be weeded out by hand, and shrubs with a base diameter up to 7 cm can be uprooted efficiently using commercially available jaw-type pullers known as "weed wrenches" (Gale, 2001). Safety measures, including gloves and goggles are recommended to protect against thorns. Mowing also can reduce the vigour of seedlings and small bushes. In the USA, mowing is most effective if repeated in early June and late August for three consecutive years (USGS, 2000).
Chemical control is the most common method of managing R. cathartica. Autumn and early winter applications of herbicides are the most effective, but efficacy declines at temperatures below 0°C (Gale, 2001). The preferred method is to cut and apply herbicide to stumps greater than 10 cm in diameter. Basal bark treatments can be applied on smaller shrubs or in areas where openings in the understorey are not necessary for restoration. Repeated treatment over several seasons is usually required to eradicate recruitment from the seed bank. Converse (1984) lists the following herbicides and methods that have been used successfully: stump applications of glyphosate in August-September; wick application of glyphosate in May; mist application of fosamine (ammonium salt) in September; frill application of picloram during the growing season; and basal application of 2,4-D in diesel fuel during the first half of the growing season. Triclopyr has been used very effectively if immediately sprayed on to cut stumps during the growing season. At temperatures above 25°C vegetable oil, such as canola (rape) is recommended as the diluent; spraying is not recommended above 28°C. Dilution with mineral oil works at temperatures between -15 and 25°C, with excellent results noted from winter applications. Diesel fuel is no longer recommended as a diluent because it is unsafe from an environmental and human safety perspective and is less effective than mineral oil. For all stem and stump applications low pump pressure is recommended to prevent spray drift. The stem must be completely encircled with the herbicide and the bark must be penetrated. Applications cannot be made to wet stems, although rain immediately after application will not normally reduce efficacy. Operations should be terminated when emulsification is noted due to low temperatures.
Malicky et al. (1970) first investigated the potential of insects as biological control agents for R. cathartica. Research in Canada on Scotosia vetulata [Philereme vetulata] and Triphosa dubitata (both Geometridae) is ongoing, but no biological control methods have been approved to date.
Current research (Gassmann et al., 2002) has identified the following insects as potential biocontrol agents for R. cathartica:
Trichochermes walkeri (Triozidae) is probably monospecific on R. cathartica. It is common and easy to rear. It impairs photosynthesis and acts as a nutrient sink for gall development. T. walkeri may also act as a vector for pathogens.
Sorhagenia janiszewskae (Cosmopterigidae) attacks both R. cathartica and Frangula alnus. It is relatively common and easy to collect, but there are problems with overwintering the adults. It bores into the above-ground parts of the target trees, and potentially impairs growth of the current year's shoots. S. lophyrella is a defoliating moth which has been found occasionally on R. cathartica and appears to have a preference for drier open habitats. The larvae start feeding very early in the season.
Philereme vetulata (Geometridae) larvae feed on the foliage of R. cathartica which reduces photosynthesis and causes water loss. It is relatively common in some areas, but more research on rearing the moth in captivity is required. P. transversata prefers R. cathartica but has been found occasionally on Frangula alnus.
Triphosa dubitata (Geometridae) is common in some areas, but little is known about culturing the moth. The larvae feed on leaves, thus impairing photosynthesis and causing water loss. Because T. dubitata appears later in the season than P. vetulata, the two species together would have an extended impact on the target host.
Ancylis derasana (Tortricidae) has been found exclusively on R. cathartica and feeds on the foliage.
Oberea pedemontana (Cerambycidae) bores into the branches and trunks of R. cathartica and Frangula alnus, causing structural damage and occasionally death of the host tree. Work with this species is handicapped by a high rate of parasitism and the time needed to complete its life cycle of 3 years.
Four species of leaf-mining Lepidoptera are associated with R. cathartica in Europe: Bucculatrix frangulella, Calybites quadrisignella, Stigmella catharticella and S. rhamnella. Their feeding activity may impair photosynthesis and cause water loss. S. catharticella is the most suitable candidate for biological control because it is relatively common. B. frangulella could be considered because it also feeds on Frangula alnus, but its usefulness is reduced by the fact that it is active late in the season.
Synanthedon stomoxiformis (Sesiidae) is the sole root-boring species on Frangula alnus and R. cathartica. However, there is evidence that it may also attack Sorbus aria (Rosaceae) and more rarely Corylus avelana (Betulaceae) as alternate hosts.
The mites Aceria rhamni and Tetra rhamni have some potential as biological control agents, and may facilitate disease transmission.
Cultural, mechanical and chemical control methods have been used in varying combinations, but no "classic" integrated control methods have been devised for R. cathartica.
ReferencesTop of page
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Distribution MapsTop of page
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