Cotoneaster horizontalis (wall-spray)
- 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
- Biology and Ecology
- Soil Tolerances
- Natural enemies
- Notes on Natural Enemies
- Means of Movement and Dispersal
- Pathway Causes
- Pathway Vectors
- Impact Summary
- Economic Impact
- Environmental Impact
- 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
- Cotoneaster horizontalis Decne.
Preferred Common Name
Other Scientific Names
- Cotoneaster davidianus hort. ex Dippel
- Cotoneaster microphyllus Diels
- Cotoneaster symonsii (hort. ex Baker) Loudon ex Koehne
International Common Names
- English: herringbone cotoneaster; rock cotoneaster; rockspray; rock-spray; wall cotoneaster
- French: cotonéaster horizontal; cotonnier horizontal
- Chinese: ping zhi xun zi; xiao ye ping zhi xun zi
Local Common Names
- Germany: Fächer-Steinmispel; Fächer-Zwergmispel; Zwergmispel waagerecht wachsende
- Italy: cotognastro orizzontale
- Netherlands: vlakke dwergmispel
- CTTHO (Cotoneaster horizontalis)
Summary of InvasivenessTop of page
Cotoneaster horizontalis is a woody, perennial, deciduous or semi-evergreen, procumbent shrub with horizontally spreading branches. It is native to parts of China, and has been introduced widely to Europe, North America, Australasia and other parts of the world as an attractive garden plant with bright red berries which often persist into winter. Introduction has been deliberate for this purpose but because the species fruits freely, has been widely planted and its seeds are so easily dispersed by birds it is now found in many places as an environmental weed, especially in western Europe but increasingly so in parts of North America, Australia and New Zealand. In such places it is seen as smothering native plant communities, altering their structure and composition. Contact with the plant can in some cases lead to dermatitis, and the berries are reputedly poisonous to children.
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Plantae
- Phylum: Spermatophyta
- Subphylum: Angiospermae
- Class: Dicotyledonae
- Order: Rosales
- Family: Rosaceae
- Genus: Cotoneaster
- Species: Cotoneaster horizontalis
Notes on Taxonomy and NomenclatureTop of page
The genus Cotoneaster includes 261 species in the temperate Old World, with many of these being apomictic aggregates (Mabberley, 2008). The genus is close to Crataegus, but its members have neither spines nor lobed leaves. Of the species C. horizontalis, Mabberley’s very brief description says “apomictic with herring-bone sprays of foliage”.
Lu and Brach (2003), in Flora of China, describe C. horizontalis and present a key for distinguishing the 59 species of Cotoneaster in China, of which 37 are endemic. These authors suggest that there are only about 90 species in the genus in the broad sense. They name two varieties of C. horizontalis: var. horizontalis, with sub-globose fruits, 5-7 mm in diameter, usually with 3 pyrenes (seeds); and var. perpusillus, with ellipsoid fruits, 3-4 mm in diameter, usually with 2 pyrenes. The same authors also mention that plants with variegated and somewhat larger leaves have been described as var. variegatus, and that C. atropurpureus and C. flinckii may be synonymous with C. horizontalis var. horizontalis. However, the Plant List (2013) gives C. horizontalis Decne. as the accepted name, with C. horizontalis var. horizontalis as one of six synonyms. C. horizontalis var. perpusillus, var. wilsonii and f. variegatus are recognized as infraspecific taxa, while C. atropurpureus Flinck & B. Hylm” and C. flinckii J.Fryer & B.Hylm” are recognized as separate species.
Dickoré and Kasperek (2010) comment that the species is variable and its taxonomy seems poorly understood and blurred by the many putative minor variants of this and other species. Further studies are needed to clarify the taxonomy of the genus, complicated as it is by hybridization and apomixis (Lu and Brach, 2003).
DescriptionTop of page
C. horizontalis is a shrub, deciduous or semi-evergreen, procumbent, usually to 50 cm tall, sometimes taller, with horizontally spreading, distichously much-branched stems (arranged in two opposite rows in the same plane, like a fish bone), the plant extending to 1-1.5 m. Branchlets blackish brown, round, initially strigose (covered in rigid straight hairs), hairless when old. Petiole 1-3 mm, pubescent; stipules readily detached, brown, narrow or lanceolate, 2-4 mm, puberulous; leaf blade suborbicular or broadly elliptic, rarely obovate, 6-14 × 4-9 mm, midvein raised abaxially and ± impressed adaxially, abaxially sparsely accumbent pubescent, adaxially glabrous, base cuneate, apex usually acute. Inflorescences 1- or 2-flowered. Pedicel short to nearly absent. Flowers 5-7 mm in diameter. Hypanthium (floral tube) campanulate, abaxially sparsely pubescent. Sepals triangular, 1-1.5 × 1-2 mm, apex acute. Petals erect, pink, reddish, or whitish, 3-4 × 2-3 mm, base shortly clawed, apex obtuse. Stamens about 12, shorter than petals. Ovary pilose apically; styles 2 or 3, free, not exceeding stamens. Fruit bright red, subglobose or ellipsoid, (3-)5-7 mm in diameter, pyrenes (‘seeds’) 3, rarely 2 (based on Lu and Brach, 2003).
Plant TypeTop of page Broadleaved
DistributionTop of page
The USDA-ARS (2015) lists C. horizontalis as native to temperate China and Taiwan, as well as Nepal but, according to Dickoré and Kasperek (2010), frequent misidentifications with other species of Cotoneaster have resulted in confusion over its native range and some records such as those from Tibet, Taiwan and Nepal may be of different species or be adventive.
In Japan, Australia, New Zealand, most of Europe, the USA and Canada, C. horizontalis has been introduced as an ornamental garden shrub and is now naturalized and often invasive in many areas (USDA-ARS, 2015). In Australia, the Queensland Government (2015) notes that C. horizontalis is sparingly naturalized in Victoria and southeastern South Australia, and possibly New South Wales. It is regarded as an environmental weed in Victoria and as a potential environmental weed in New South Wales, Tasmania and the Australian Capital Territory. The same source indicates that the species is naturalized in Washington and Oregon in northwestern USA. In British Columbia in western Canada, according to the Garry Oak Ecosystems Recovery Team (2015), C. horizontalis (rock cotoneaster) has escaped from gardens on southern Vancouver Island, the Gulf Islands, the Sunshine Coast and the lower Fraser Valley, and has been present in Garry oak (Quercus garryana) ecosystems in British Columbia since 2002.
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||Reference||Notes|
|-Guizhou||Present||Native||USDA-ARS, 2015; USDA-ARS, 2015|
|-Tibet||Present||Native||USDA-ARS, 2015||disputed native range|
|Nepal||Present||Native||USDA-ARS, 2015||disputed native range|
|Taiwan||Present||Native||USDA-ARS, 2015||disputed native range|
|Egypt||Present only in captivity/cultivation||Introduced||Not invasive||Khalifa and Loutify, 2006|
|Canada||Present||Present based on regional distribution.|
|-British Columbia||Localised||Introduced||Garry Oak Ecosystems Recovery Team, 2015|
|USA||Present||Present based on regional distribution.|
|-California||Present, few occurrences||Introduced||2007||Jacobson and Zika, 2009||First collection for California as an escape from cultivation: Del Norte County, pasture edge, 3 air km N of Lake Earl, elev. 8 m, 18 July 2007|
|Argentina||Present, few occurrences||Introduced||Giorgis et al., 2011||Cordoba mountains, 1825 m|
|Austria||Widespread||Introduced||NOBANIS, 2015||very common, first recorded 1935 but introduced earlier|
|Belgium||Localised||Introduced||1982||Invasive||Dickoré and Kasperek, 2010; Verloove, 2013; NOBANIS, 2015||first noted in the wild in 1982|
|Czech Republic||Present||Introduced||Invasive||Dickoré and Kasperek, 2010|
|Denmark||Present, few occurrences||Introduced||Not invasive||NOBANIS, 2015||rare|
|France||Widespread||Introduced||Invasive||Farille et al., 2010; Tela Botanica, 2015|
|Germany||Present||Introduced||Invasive||Dickoré and Kasperek, 2010; NOBANIS, 2015|
|Hungary||Present||Introduced||Invasive||Dickoré and Kasperek, 2010|
|Ireland||Widespread||Introduced||Invasive||NOBANIS, 2015||common, potentially invasive|
|Italy||Localised||Introduced||Not invasive||Celesti-Grapow et al., 2010||naturalized in Lombardy and casual occurrences in Alto-Adige, Trentino and Veneto|
|Lithuania||Present, few occurrences||Introduced||1992||Not invasive||NOBANIS, 2015||rare, first record 1992|
|Luxembourg||Present||Introduced||Invasive||Dickoré and Kasperek, 2010|
|Netherlands||Present, few occurrences||Introduced||Not invasive||Dickoré and Kasperek, 2010||rare, potentially invasive|
|Norway||Present||Introduced||1982||Invasive||NOBANIS, 2015||first record 1982|
|Poland||Present||Introduced||Invasive||Dickoré and Kasperek, 2010|
|Sweden||Present, few occurrences||Introduced||1969||Invasive||Hylmo, 1993||rare|
|Switzerland||Present||Introduced||Invasive||Dickoré and Kasperek, 2010|
|-Channel Islands||Present||Introduced||BSBI, 2015|
|-New South Wales||Present||Introduced||Queensland Government, 2015||Possibly naturalized, potential environmental weed|
|-South Australia||Present||Introduced||Queensland Government, 2015||Sparingly naturalized in the south-east|
|-Tasmania||Present||Introduced||Queensland Government, 2015||potential environmental weed|
|-Victoria||Present||Introduced||Queensland Government, 2015||Sparingly naturalized, environmental weed|
|New Zealand||Present||Introduced||Webb et al., 1988; USDA-ARS, 2015|
History of Introduction and SpreadTop of page
C. horizontalis is native to western China, where, according to Lu and Brach (2003), it is found in several provinces at altitudes of 1500 to 3500 m. From there, after it was recognized by European plant collectors in the late nineteenth century as a potentially attractive garden species, specimens were taken to western Europe and then on to North America and Australasia. In 1916 the Arnold Arboretum in Boston, USA, recognized it as having been “first raised in France forty years ago” (i.e., around the 1860s-1870s) and had been growing in the Arboretum for about twenty five years (Arnold Arboretum, 1916), continuing “this is an excellent plant for a large rock garden, and in Europe it is often trained to cover low walls, for which purpose it is well suited”. This and other favourable descriptions no doubt led to its wide adoption as a garden plant.
According to Pilkington (2011), C. horizontalis has been a highly popular garden plant in Britain since around 1889 when it was first introduced into cultivation. However, from 1940 onwards naturalized plants of this species began to be recorded from the wild in Britain, with subsequent rapid spread; in 1969, for example, sampling of 10-km grid squares centred around Oxfordshire recorded the species in 53, and 30 years later it was found in 961 squares, with the strongest populations apparently associated with light soils in southern England. It has also been observed in the wild in the Republic of Ireland and France (Pilkington, 2011). In Belgium the first observation of the plant in the wild was in 1982 and it is now classed as a ‘black list’ alien invasive weed with high environmental risk (Belgian Forum on Invasive Species, 2015).
IntroductionsTop of page
|Introduced to||Introduced from||Year||Reason||Introduced by||Established in wild through||References||Notes|
|Natural reproduction||Continuous restocking|
|France||China||1860-1870s||Horticulture (pathway cause)||Yes||Arnold Arboretum (1916)|
|New Zealand||1994||Horticulture (pathway cause)||Yes||New Zealand Plant Conservation Network (2015)||first reported naturalized in 1994|
|UK||1889||Horticulture (pathway cause)||Yes||Pilkington (2011)||first introduced into cultivation 1889, naturalized from about 1940 onwards|
|USA||Europe||1880||Horticulture (pathway cause)||Yes||Slabaugh and Shaw (2008)||first introduced into cultivation 1880|
Risk of IntroductionTop of page
Although C. horizontalis is widely grown in many gardens in temperate climates and has escaped and naturalized in several countries, it could spread yet further in those countries, and might also become naturalized in countries in which it is at present confined to gardens.
According to a risk assessment undertaken by Boer (2014), scores of 3 (high risk) were given to C. horizontalis and other small-leaved Cotoneaster species in Belgium for: (i) dispersion potential or invasiveness; (ii) colonization of high conservation value habitats; and (iii) adverse impacts on native species. There was also a medium risk (score 2) of alteration of ecosystem functions. Taking into account the situation in Belgium, the risk of establishment of C. horizontalis in neighbouring Netherlands was considered high.
HabitatTop of page
The Flora of China (Lu and Brach, 2003) describes the native habitat of C. horizontalis as thickets, rocks, rocky slopes and dry mountain areas from 1500 to 3500 m. Similarly, where it has been introduced and become naturalized, it grows in rocky situations and, in urban areas, in cracks in stone walls, along roadsides, on house walls, along railways and in industrial areas (Dickoré and Kasperek, 2010).
In Belgium C. horizontalis has invaded calcareous grasslands considered biodiversity hotspots, and other high value habitats like sand dunes, as well as large urban centres (Piqueray et al., 2008). It is less common in eastern Belgium, however, where soils tend to be more acidic. In Britain too it invades limestone grassland, limestone pavement and cliffs, as well as railway banks, quarries, pavements, chalk pits and walls. It seems particularly fond of light, well-drained calcareous substrates (Pilkington, 2011). In Germany, C. horizontalis is found in rocky situations but also dry calcareous grassland with rocky outcrops such as in northern Hesse and in the Jura of Baden Württemberg and Bavaria (Dickoré and Kasperek, 2010).
In southeastern Australia, the species appears to have the potential to become an invasive weed in subalpine and alpine vegetation, particularly on rocky slopes (Queensland Government, 2015).
C. horizontalis is a shade intolerant shrub. In its native environment in China it seems able to colonize openings in the canopy regardless of slope aspect. In Mianning County in Sichuan Province it is an extremely abundant shrub on south-facing slopes (Jarvis and Liu, 1993).
Habitat ListTop of page
|Terrestrial – Managed||Cultivated / agricultural land||Principal habitat||Productive/non-natural|
|Rail / roadsides||Secondary/tolerated habitat||Natural|
|Urban / peri-urban areas||Secondary/tolerated habitat||Harmful (pest or invasive)|
|Urban / peri-urban areas||Secondary/tolerated habitat||Natural|
|Urban / peri-urban areas||Secondary/tolerated habitat||Productive/non-natural|
|Buildings||Secondary/tolerated habitat||Harmful (pest or invasive)|
|Terrestrial ‑ Natural / Semi-natural||Natural grasslands||Secondary/tolerated habitat||Harmful (pest or invasive)|
|Rocky areas / lava flows||Principal habitat||Natural|
|Scrub / shrublands||Principal habitat||Natural|
|Arid regions||Principal habitat||Natural|
|Coastal dunes||Secondary/tolerated habitat||Harmful (pest or invasive)|
Hosts/Species AffectedTop of page
Piqueray et al. (2008) compared plots invaded by C. horizontalis with uninvaded plots in calcareous grassland in the vicinity of Dinant in southern Belgium and found that the species reduced the area of rocky or bare ground, leading to an increase in moss cover. Its presence also reduced the richness and diversity of the grassland, the four species whose incidence was most significantly reduced being Allium sphaerocephalon, Bromus erectus, Festuca lemanii and Lactuca perennis. Four other species were also affected, but not significantly so.
Biology and EcologyTop of page
In Germany, both triploid (2n = 3x = 51) and tetraploid (2n = 4x = 68) individuals have been identified (Piqueray et al., 2008). In Britain, Pilkington (2011) describes C. horizontalis as an apomictic tetraploid, while Zika (2013) also reports the species as tetraploid.
Although C. horizontalis is apomictic, producing seed without pollination and subsequent fertilization, it can also set seed after pollination. The dark red-pink flowers are bisexual, epigynous (the ovary is below the petals and sepals), borne in small clusters, pollinated by insects and abundant in spring (Pilkington, 2011).
Pilkington (2011) as well as Dickoré and Kasperek (2010) say that plants are self-layering; where tips of the aerial branches of C. horizontalis contact the ground they can root and form daughter plants.
Physiology and Phenology
C. horizontalis flowers May-June and fruits September-October in the northern hemisphere (Lu and Brach, 2003).
Germination usually takes between 1 and 18 months but seeds can sometimes remain viable for 5 years (Pilkington, 2011). Seeds are dormant when fresh and fruits contain inhibitory substances in the fleshy fruit coat which delay germination. Stratification in the soil at 5oC for 3-4 months, 1.5-3 hours in sulfuric acid or exposure to alternating temperatures of 15o and 24oC can break seed dormancy (Grbic and Skocajic, 2004). Germination rates for plants invading calcareous grasslands in Belgium were found to be around 30% (Frisson et al., 2008).
He (2011), in studies on the growth and development of C. horizontalis in its native China, found that additional nitrogen and/or potassium helped improve flowering rate. In calcareous grassland in Belgium, flowering was observed in every plant over 4 years of age (Piqueray, 2008), while the capacity for fruiting was noted in plants at 3 years (Frisson et al., 2008).
According to the Royal Horticultural Society (2015), C. horizontalis takes 10-20 years to attain its final height and spread. Piqueray et al. (2008) observed 14-year-old plants growing in the wild in invaded calcareous grasslands in Belgium. The USDA-NRCS (2015) describes the lifespan of this species as moderate.
Population Size and Structure
C. horizontalis invading calcareous grasslands in Belgium was observed to have a population density between 0.34 and 10 individual plants per hectare, with a high proportion of small young individuals in the most highly invaded areas (Frisson et al., 2008).
Jarvis and Liu (1993) describe species associated with C. horizontalis in its native environment among Pinus yunnanensis - sclerophyllous broadleaved forests in Sichuan Province of China. Piqueray et al. (2008) recorded species of plants growing close to C. horizontalis in calcareous grasslands in Belgium, indicating that it mostly occurred in complexes of xeric grasslands and calcareous rock; some plants were found at the edges or grasslands or under scrub.
Webber et al. (2012) observed insect visitors to C. horizontalis (and other plant species, both native and exotic) in Christchurch Botanic Gardens in New Zealand. They listed visits by six native insects, with the commonest being a ‘black hoverfly’, and visits by seven species of exotic (introduced) insects, with by far the commonest visitors being bumblebees, followed by honey bees (Apis mellifera) and ‘drone flies’. The behaviour of honey bees feeding on C. horizontalis flowers is described by Pflumm (1983). In Britain the plant attracts large numbers of wasps (Vespula vulgaris) as well as bees (Ian Popay, personal observation, 2014). In addition, the ants Formica fusca and Lasius alienus have been observed exclusively in early May feeding on pollen and nectar from the flowers (Carvalheiro et al., 2008).
One of the reasons for the popularity of the species as a garden plant is its small bright red fruits which make a bold garden display in autumn and into winter. According to Pilkington (2011) ripe fruits are eaten by thrushes and finches which then disperse the seeds in their droppings.
C. horizontalis appears to perform best where it has been introduced to areas with cooler temperate climates like the northern USA, southern Canada and northern Europe. In North America the species does well on dry, rocky sites (Garry Oak Ecosystems Recovery Team, 2015). Similarly in Europe, it is best suited to dry, rocky ground, similar to its habitat in its native China. It has been found invading dry calcareous grasslands in Belgium (Piqueray et al., 2008), England (Pilkington, 2011; Larkin, 2012) and Germany (Dickoré and Kasperek, 2010).
Pilkington (2011) reports that the species grows particularly well in light, well-drained calcareous substrates, and is appreciated by gardeners for its toughness and tolerance of north and east-facing situations. It also seems to be tolerant of dry and nutrient-poor sites. According to the Royal Horticultural Society (2015), C. horizontalis tolerates chalk, clay, loam and sandy soils with a pH ranging from acid to alkaline. In experiments testing the salt tolerance of some ornamental shrubs, Marosz (2004) found that C. horizontalis was not affected by soil salinity of 12 mS cm−1 electrical conductivity.
In its native environment in China, C. horizontalis occurs at altitudes of 1500 to 3500 m. In the Alps of Europe, according to Dickoré and Kasperek (2010), it ascends to at least 1000 m.
ClimateTop of page
|Cf - Warm temperate climate, wet all year||Tolerated||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|
|Cw - Warm temperate climate with dry winter||Preferred||Warm temperate climate with dry winter (Warm average temp. > 10°C, Cold average temp. > 0°C, dry winters)|
|Dw - Continental climate with dry winter||Preferred||Continental climate with dry winter (Warm average temp. > 10°C, coldest month < 0°C, dry winters)|
Soil TolerancesTop of page
Special soil tolerances
Natural enemiesTop of page
|Natural enemy||Type||Life stages||Specificity||References||Biological control in||Biological control on|
|Agrilus sinuatus||Herbivore||Stems||not specific||Pilkington, 2011|
|Athrips rancidella||Herbivore||Leaves||not specific||Pilkington, 2011|
|Corythucha cydoniae||Herbivore||Leaves||not specific||Pilkington, 2011|
|Eriophyes pyri||Herbivore||Fruits/pods/Leaves||not specific||Pilkington, 2011|
|Erwinia amylovora||Pathogen||Whole plant||not specific||Obradovic and Ivanovic, 2013|
|Odocoileus virginianus||Herbivore||Whole plant||not specific||Fargione et al., 1991|
|Phytophthora ramorum||Pathogen||Growing point/Leaves||not specific||Bulajic et al., 2010|
Notes on Natural EnemiesTop of page
Where C. horizontalis occurs in North America, browsing by white-tailed deer (Odocoileus virginianus) can cause severe damage (Fargione et al., 1991), although Dickoré and Kasperek (2010) say that the species is highly resistant to cutting and to grazing. According to Pilkington (2011), pests in the USA include the hawthorm lace bug (Corythucha cydoniae), the cotoneaster webworm (Athrips rancidella), scale and spider mites, sinuate pear tree borer (Agrilus sinuatus) and pear leaf blister mite (Phytoptus pyeri [Eriophyes pyri]).
Cotoneaster species are susceptible to fireblight (caused by Erwinia amylovora), but this is more likely to be a problem with larger and later flowering species, although its presence on C. horizontalis has been reported in Serbia (Obradovic and Ivanovic, 2013) and Turkey (Bastas and Sahin, 2012). Leaf spots and canker have been reported in the USA. The fungal disease Phytophthora ramorum has been found on ornamental specimens of C. horizontalis in Serbia (Bulajic et al., 2010).
Means of Movement and DispersalTop of page
Self-layering, the rooting of arching tips of branches and establishment of new plants, can be a method of local spread of established C. horizontalis plants (Pilkington, 2011).
Vector Transmission (Biotic)
In many countries, and presumably in its native China, the bright red berries are attractive to birds that eat them and excrete the seeds, although most dispersal would be fairly localized to areas around the birds’ roosts (Verloove, 2013).
As a popular garden plant, its further spread from cultivation seems inevitable. Viable propagules (berries, seeds) can easily be dispersed through improper disposal of cuttings and other garden waste.
C. horizontalis has already been introduced to many temperate countries as an attractive garden plant and its further spread in those countries is inevitable since it is readily available in garden centres and also as seeds from websites (Halford et al., 2011). It is much promoted in gardening journals and newspaper columns (see for example Dusoir, 2002). In several countries where C. horizontalis is recognized as an invasive alien, its planting in the wild is prohibited. The New Zealand Department of Conservation (2015), for example, regards the species as threatening forest and shrubland, as well as grasslands, cliffs and riverbeds and classes it as a Category C invasive weed, which is “potentially troublesome and should not be spread around”.
Pathway CausesTop of page
|Digestion and excretion||Yes||Yes|
|Escape from confinement or garden escape||Yes||Dickoré and Kasperek, 2010|
|Garden waste disposal||Yes|
|Landscape improvement||Yes||Yes||Dickoré and Kasperek, 2010|
|Ornamental purposes||Yes||Yes||Dickoré and Kasperek, 2010|
Pathway VectorsTop of page
|Debris and waste associated with human activities||Yes|
Impact SummaryTop of page
Economic ImpactTop of page
Pilkington (2011) points out that in urban areas the species has the potential to damage buildings by rooting in crumbling mortar and cracks, and can be costly to eradicate from wildlife areas. Investigations into the costs and efficacy of techniques for controlling C. horizontalis and other invasive species in invaded ecosystems in Belgium found that invasive plant management is usually expensive and hard to implement but some techniques showed encouraging results (Mahy and Halford, 2009; Frisson et al., 2010).
Environmental ImpactTop of page
Impact on Habitats
C. horizontalis is one of the alien plant species invading lowland calcareous (chalk) grassland in the Wild Park Local Nature Reserve near Brighton in the South Downs of southern England (Larkin, 2012), and its impacts in calcareous grasslands in Belgium have been described by Piqueray et al. (2008). In northern Victoria, Australia, C. horizontalis has escaped from gardens in the Mt Buffalo National Park and spread to nearby alpine slopes (Queensland Government, 2015).
Impact on Biodiversity
Species richness of calcareous grasslands in Belgium is significantly lower on plots invaded by C. horizontalis (Frisson et al., 2008), so that locally it may pose a serious threat to biodiversity (Pilkington, 2011). Impact assessments carried out by Piqueray et al. (2008) indicated that the presence of C. horizontalis was associated with changes in both the structure and composition of calcareous grassland communities, caused by decreasing species richness and diversity and directly affecting grassland specialist species; they found significant reductions in invaded grasslands in populations of Allium sphaerocephalon, Bromus erectus, Festuca lemanii and Lactuca perennis. Four other species were also affected, but not significantly so. It is expected that these impacts will intensify over time as the C. horizontalis plants grow larger and cover more ground.
In the complex interrelationship between calcareous grasslands, black ants (Lasius alienus) and the silver-studded blue (Plebejus argus), a rare and declining heathland butterfly confined to small colonies in Britain, large areas of sparse grassland and bare ground are essential to encourage black ants, which in turn tend the butterfly’s larvae and chrysalises in spring, sometimes in their nests, and the adult butterfly as it emerges in summer. A 10-year study in Broadcroft Quarry in Dorset showed a loss in area of bare ground, the most suitable breeding habitat for the silver-studded blue, due to the spread of invasive plants such as bramble (Rubus fruticosus), Clematis, coarse grasses and the non-native C. horizontalis. These shaded out the main larval food plant, bird's-foot trefoil (Lotus corniculatus), and made conditions unsuitable for ants (de Whalley et al., 2006).
Threatened SpeciesTop of page
Social ImpactTop of page
Weller and Ormerod (1996) reported contact dermatitis in a 43-year-old woman after contact with pruning waste of C. horizontalis. In addition, the fruits are said to be poisonous to humans; containing cyanogenic glycosides, the berries are toxic if eaten in large quantities, especially by children (HerbiGuide, 2015). The Royal Horticultural Society (2015) notes that ingestion of berries results in a mild stomach upset.
Risk and Impact FactorsTop of page Invasiveness
- Proved invasive outside its native range
- Has a broad native range
- Pioneering in disturbed areas
- Benefits from human association (i.e. it is a human commensal)
- Long lived
- Has high reproductive potential
- Reproduces asexually
- Altered trophic level
- Ecosystem change/ habitat alteration
- Reduced native biodiversity
- Threat to/ loss of endangered species
- Threat to/ loss of native species
- Causes allergic responses
- Competition - shading
- Highly likely to be transported internationally deliberately
- Difficult/costly to control
UsesTop of page
C. horizontalis is widely grown as an ornamental low-maintenance ground cover on banks and slopes, and as a hedge or screen against walls. It is considered very decorative, due to the orange and red autumnal colour of the leaves and the bright red fruits which make a bright and cheerful display in autumn and winter (Royal Horticultural Society, 2015).
When Sokkar et al. (2013) explored the antioxidant, anticancer and hepatoprotective properties of C. horizontalis, they found that ethanolic extracts of the branches contained β-carotene, ascorbic acid and lesser amounts of α-tocopherol and amygdalin. Toxicity testing showed that the ethanolic extracts could be considered as a potential source of natural antioxidant with hepatoprotective, hypolipidaemic and other properties.
The flowers of C. horizontalis are highly attractive to bees and other insects as sources of nectar, while the berries attract birds and help sustain them through the winter (Pilkington, 2011). When grown against a wall, the plant provides sheltered nesting and roosting sites for birds.
Uses ListTop of page
- Landscape improvement
- Wildlife habitat
- garden plant
Similarities to Other Species/ConditionsTop of page
Lu and Brach (2003) stressed that the taxonomy of the genus needs clarification, especially since species hybridize and many of the species are apomictic. These two complications will continue to dog the identification of this and other Cotoneaster species in the future.
Dickoré and Kasperek (2010) describe the species of Cotoneaster found in Central Europe and mention several species with which C. horizontalis might be confused there. C. apiculatus is similar to C. horizontalis but has larger, almost circular, leaves. C. divaricatus has in the past been misidentified as C. horizontalis and young plants can be very similar. However it has a more erect habit, larger, more oblong leaves and cylindrical fruit. C. nitidus also resembles C. horizontalis in its regular distichous branches but the backs of the leaves are covered with short hairs lying flat on the surface, the inflorescences are 2-6 flowered, the peduncles reflexed and the fruits scarlet in colour. C. verruculosus is also similar but differs in its reduced indumentum, with bases of hairs giving a characteristic prickly appearance to the shoots. C. nitens is also similar in habit but is rarely planted in Central Europe and has black cylindrical fruit.
In New Zealand, C. conspicuus is similar to C. horizontalis but can be distinguished by its slightly arching branches (not in a herring-bone pattern), spreading rather than erect petals, and its scarlet rather than crimson fruits (Heenan et al., 1998).
Prevention and ControlTop of page
Halford et al. (2011) estimated that C. horizontalis was present in 53% of the sales catalogues of horticulturalists in southern Belgium and pointed out that as long as the species is used in the vicinity of calcareous grasslands, propagules are continuously provided, thus jeopardizing management actions. Pilkington (2011) also points out that C. horizontalis is sold by many garden centres and nurseries and adds that prevention measures should focus on discouraging its planting close to wildlife sites that support dry or rocky limestone grassland and other habitats. Piqueray et al. (2008) also stressed the need to prevent its commercialization and to intensively manage high-value habitats.
In Belgium, Piqueray et al. (2008) suggest that information campaigns in high-risk areas would raise public awareness and early management of infestations. Dickoré and Kasperek (2010) say that the common practice of large-scale planting of mass produced non-native species, such as C. horizontalis, in the open landscape should be “considered a dangerous potential pool of new plant invaders and a deliberate threat to native flora” and should be discouraged. Pilkington (2011) recommends that the Landscape Institute (in Britain) and local authorities should be lobbied to discourage mass plantings in landscape schemes or new developments.
Halford et al. (2011) surveyed the attitudes of nurserymen (producers and sellers in horticultural federations) and private managers (landscape architects and garden contractors) to the possible introduction of codes of conduct on the use of invasive garden plants in Belgium and found that 61% of nursery men and 73% of private managers would be prepared to endorse such a code of conduct. Furthermore, 86% of gardeners would agree to buy their ornamental plants in nurseries espousing such a code.
Frisson et al. (2008) and Pilkington (2011) stress that, once established in wildlife areas, C. horizontalis is expensive and difficult to remove. Dickoré and Kasperek (2010) say that complete eradication of alien Cotoneaster species, other than on a very expensive, local and temporary scale, would “simply be impossible”.
Frisson et al. (2008) and Mahy and Halford (2009) tested both mechanical and chemical management techniques in calcareous grasslands, where highly selective techniques are needed for environmental reasons. They tried pulling, cutting, stump burning, spraying, cutting plus glyphosate application on stump or on stems. Efficiency, cost, feasibility and side-effects on ecosystems were estimated. Spraying and single cutting are not deemed efficient since resprouting occurs. The authors concluded that the best control method available was to cut and paint the stump with glyphosate.
The Tamar Valley Weed Strategy Working Group (2015) recommends grubbing cotoneasters at any time of the year, taking care to remove seedlings and small bushes using a mattock or spade. Pilkington (2011) also suggests care should be taken that fruits do not fall on the ground. The same author says that removing stumps and roots is vital as otherwise they can resprout, a comment echoed by the Garry Oak Ecosystems Recovery Team (2015). The latter group also suggests that cotoneaster plants should be removed when the soil is moist and that disturbed soil should be immediately replanted with desirable native species to prevent reinfestation.
Mechanical scraping was used in Broadcroft Quarry, Dorset, UK, to remove the rich topsoil and C. horizontalis roots to encourage the establishment and development of a less competitive, low nutrient-requiring calcareous flora (de Whalley et al., 2006).
The Garry Oak Ecosystems Recovery Team (2015) suggest that seedlings can be smothered with mulch or black plastic, but warn that burning is not effective for controlling regeneration. Jarvis and Liu (1993) point out that C. horizontalis regenerates quickly after fire.
Mahy and Halford (2009) found pulling plants from the soil manually was extremely difficult and ineffective.
To kill small shrubs and control regrowth, the herbicides glyphosate or triclopyr can be applied as a wiper or by handheld sprayer when plants are actively growing between spring and autumn. Alternatively, these herbicides can be applied to cut stumps or to abraded bark (Pilkington, 2011; Garry Oak Ecosystems Recovery Team, 2015).
ReferencesTop of page
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ContributorsTop of page
21/10/2014 Original text by:
Ian Popay, Consultant, New Zealand
Distribution MapsTop of page
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