The biology of invasive alien plants in Canada. 9 ...

The Biology of Invasive Alien Plants in Canada. 9. Impatiens glandulifera Royle David R. Clements1, Kathleen R. Feenstra1, Karen Jones2, and Richard Staniforth2 1

Can. J. Plant Sci. Downloaded from pubs.aic.ca by 108.172.120.224 on 06/20/15 For personal use only.

Department of Biology, Trinity Western University, 7600 Glover Rd., Langley, British Columbia, Canada V2Y 1Y1; and 2Biology Department, University of Winnipeg, 515 Portage Avenue, Winnipeg, Manitoba, Canada R3B 2E9. Received 9 November 2006, accepted 21 November 2007. Clements, D. R., Feenstra, K. R., Jones, K. and Staniforth, R. 2008. The Biology of Invasive Alien Plants in Canada. 9. Impatiens glandulifera Royle. Can. J. Plant Sci. 88: 403417. Impatiens glandulifera Royle (Himalayan balsam) is an invasive alien annual up to 3 m in height with showy flowers that are generally pink or purplish. Native to the Himalayan region, I. glandulifera was first recorded in Canada in 1901 in Ottawa, and is now found in eight Canadian provinces: British Columbia, Manitoba, Ontario, Quebec, Nova Scotia, New Brunswick, Prince Edward Island and Newfoundland. Impatiens glandulifera is typically found in riparian habitats and may spread rapidly because its seeds are readily transported via waterways. Up to 2500 seeds are produced per plant and dispersed explosively up to 5 m from the parent plant. This can result in dense monotypic stands which prevent establishment of native plants and make stream banks vulnerable to erosion when the shallow-rooted plants die back. Impatiens glandulifera is susceptible to glyphosate but because herbicide use in riparian areas is not advised, other control methods such as hand weeding, mowing or flaming have been used. Methods for eradication are most successful when upstream populations are controlled first, as the plants spread downstream. Removal of I. glandulifera should be managed synchronously with non-native control measures and ideally be accompanied by planting native species to ensure the restoration of native species composition. The prognosis for curbing its spread in Canada seems poor as it has quite rapidly become established along waterways in many regions, following a pattern seen over the past two centuries in Europe. Key words: Impatiens glandulifera, Impatiens roylei, Himalayan balsam, impatiente glanduleuse, policeman’s helmet riparian, invasive plant, weed biology Clements, D. R., Feenstra, K. R., Jones, K. et Staniforth, R. 2008. La biologie des plantes exotiques envahissantes au Canada. 9. Impatiens glandulifera Royle. Can. J. Plant Sci. 88: 403417. Impatiens glandulifera Royle (impatiente glanduleuse) est une annuelle envahissante pouvant mesurer jusqu’a` trois me`tres de hauteur. Ses fleurs tre`s voyantes sont geńe´ralement roses ou mauves. Cette plante originaire de l’Himalaya a e´te´ signaleé pour la premie`re fois a` Ottawa en 1901, mais on la retrouve a` pre´sent dans huit provinces (Colombie-Britannique, Manitoba, Ontario, Que´bec, Nouvelle-Ećosse, Nouveau-Brunswick, Iˆle-du-Prince-E´douard et Terre-Neuve). Impatiens glandulifera affectionne habituellement les milieux riverains et se multiplie rapidement, car les cours d’eau en transportent aise´ment les graines. Chaque plant donnera jusqu’a` 2500 semences qui seront disperseés de manie`re explosive jusqu’a` 5 me`tres de distance de la plante me`re. Il en dećoule parfois de denses peuplements monotypiques qui empeˆchent les plantes indige`nes de s’e´tablir et peuvent rendre les berges vulne´rables a` l’e´rosion lorsque meurent ces plantes peu profonde´ment enracineés. Impatiens glandulifera est sensible au glyphosate, mais l’usage d’herbicides e´tant dećonseille´ dans les zones riveraines, on recourt a` d’autres me´thodes de lutte, notamment le de´sherbage manuel, la tonte ou le bruˆlis. L’e´radication est plus efficace quand on commence par controˆler les peuplements en amont, l’espe`ce essaimant en aval. A` l’e´radication de cette plante devraient s’ajouter des mesures de lutte contre les plantes introduites et la plantation d’espe`ces indige`nes qui assureront la restauration de la flore naturelle. Les efforts pour freiner la propagation de l’impatiente glanduleuse au Canada ne promettent gue`re, car la plante s’est e´tablie tre`s rapidement en bordure des cours d’eau dans maintes re´gions, reproduisant ainsi une situation qui se perpe´tue depuis deux sie`cles en Europe. Mots cle´s: Impatiens glandulifera, Impatiens roylei, impatiente glanduleuse, Himalayan balsam, policeman’s helmet riverain, plante envahissante, biologie des mauvaises herbes

large touch-me-not, glandular touch-me-not, ornamental jewelweed, balsam, balsamine geánte, and Balsamine de l’Himalaya (Hitchcock and Cronquist 1973; Burbridge 1989; Douglas et al. 1998; Darbyshire 2003; USDA 2004). Impatiens is Latin for impatient, ascribed to the sudden bursting of the capsules upon contact (Fernald 1950). Bayer (EPPO) code: IPAGL. Balsaminaceae (Touch-me-not family), Balsaminaceés.

1. Names Impatiens glandulifera Royle; Synonym: Impatiens roylei Walp. Himalayan balsam; impatiente glanduleuse (Darbyshire 2003). Other common names include: Indian Balsam, policeman’s helmet, jumping jack, jewelweed, 403


404 CANADIAN JOURNAL OF PLANT SCIENCE

2. Description and Account of Variation (a) Species Description * The following description is based on characteristics of Canadian populations supplemented with published information (Fernald 1950; Clevenger 1971; Valentine 1971; Hitchcock and Cronquist 1973; Grey-Wilson 1980; Burbridge 1989; Beerling and Perrins 1993; Ennos et al. 1993; Douglas et al. 1998; Gilkey and Dennis 2001; Graham 2003). Annual herb from 0.6 m to 2 (3) m in height (Fig. 1a). Roots simple, 1520 cm long, numerous, lignified outside with a central watery pith, often adventitious and whorled at nodes and base of stalk, some with branchlets, forming an inverted cone from the stem base (Fig. 1e). Stems are erect to ascending, sometimes branched, purplish-tinged, 550 mm wide, woody, glabrous, and hollow for most of their length (Fig. 1b), and with a central watery pith. Stem branches feature fingerlike glandular stipules in the nodes (Fig. 1b). Leaves are opposite or in whorls of three, lanceolate to elliptic (Fig. 1d), shiny with pinkish veins. Petioles are 25 cm long. The leaves measure 615 cm in length and are sharply serrated along the edges, with 1850 teeth on each side. Flowers 1 or more in axillary racemes, pinkish to purplish red, often purple spotted, hypogynous (floral parts attached below the ovary), zygomorphic (bilater-

ally symmetrical); sepals 2, formed by twisting action of the pedicel into a pouch 720 mm long and 917 mm wide, contracted into a downward curling spur 27 mm long; petals 5, 1 dorsal petal 1217 mm long and 68 mm wide, forming a hood above the androecium (all stamens) and 4 lateral petals 79 mm long and 57 mm wide (Fig. 2a, b). Fruit capsules are elastically dehiscent (will burst if touched when the pod is ripe), 1.52.5 cm in length, and contain many spherical seeds 47 mm in diameter, with seed colour varying from green to brown to black at maturity (Graham 2003; Fig. 2c, d). Cotyledons, bi-lobed approximately 1 cm long (Fig. 1c). No chromosome counts are available for Canadian or North American material. Jones and Smith (1966) reported chromosome numbers of either n 10 or n 9 from I. glandulifera growing at Kew Gardens in the United Kingdom. Khoshoo (1957) reported 2n20 for I. glandulifera growing in its native India, suggesting that it is essentially n 10 and that 2n18 plants represent ‘‘derivatives’’ (Jones and Smith 1966). However, Cˇheshmedziez (1994) also recorded 2n18 for plants from the Central Rhodopes Mountains in Bulgaria. This variation is possibly associated with differences in chromosome morphology (Valentine 1971), but further investigation is required. Genome size (i.e.,

Fig. 1. Vegetative characteristics of Impatiens glandulifera. (a) habit of plant, (b) stem/branch node showing finger-like glandular stipules, (c) seedling at cotyledon stage, (d) foliage leaf, (e) base of stem showing swollen first node and adventitious roots on the soil surface. Illustrated by R. Staniforth.


CLEMENTS ET AL. * IMPATIENS GLANDULIFERA ROYLE 405

Fig. 2. Reproductive characteristics of Impatiens glandulifera. (a) flower, anterior view, (b) flower, side view (c) seed side view (upper) and cross-sections (lower), (d) side view of intact capsule (upper), side view of dehisced capsule (lower). Illustrated by R. Staniforth.

referring to the amount of nuclear DNA in an unreplicated gametic nucleus) is 1127 Megabase pairs (Bennett and Smith 1991; Bennett and Leitch 2004). (b) Distinguishing Features * All Impatiens species share a similar floral structure and explosive pods. Impatiens glandulifera can be distinguished from all but one of the native North American or introduced species reported in Canada by its usually greater height, robust somewhat woody stems, opposite or whorled leaves, and the pinkish to purplish colour of its flowers (Scoggan 1978). The exception is the occasional garden escape, I. balsamifera L. (Darbyshire 2003), an annual to perennial plant whose flowers are similar in colour range, but are larger with more prominent spurs (2.53.5 cm as compared with 27 mm for I. glandulifera), and whose stems reach only 60 cm in height (Pacific Island Ecosystems at Risk 2007). The other species in Canada are shorter, more delicate plants with alternate leaves and yellowish to orange and brownish flowers, often spotted. These include the native I. aurella Rydb. and I. ecalcarata Blank in British Columbia (Douglas et al. 1998), I. capensis Meerb. in all Canadian provinces (Darbyshire 2003) and I. pallida Nutt. in Ontario (Newmaster et al. 1998) as well as I. noli-tangere L., that is possibly native in western North America as well as Eurasia and present in Manitoba, Saskatchewan and British Columbia (Hatcher 2003), and I. parviflora DC., native to Europe and collected from Nova Scotia to Ontario and from British Columbia (DAO Herbarium).

(c) Intra-specific Variation * Impatiens glandulifera exhibits significant phenotypic variation which may be due largely to differences in soil moisture or climate regime (Beerling and Perrins 1993; Kollmann and Ban˜uelos 2004). The usual form of the plant is tall with a small number of branched stems although shorter, many-branched specimens with shorter leaves and internodes do occur (Beerling and Perrins 1993). The variation in flower colour from white to pink to purple that is seen in North America is also seen throughout its range in Europe (Valentine 1971; Beerling and Perrins 1993; Douglas et al. 1998). For example, in the United Kingdom five colours occur: purple, pink, lilac, white and blue (rare), with pink and lilac being the most dominant, whereas northern Holland populations are dominantly pale pink (Valentine 1971). Variation also occurs in tolerance to frost; plants found in the Himalayas are more frost tolerant than European populations (Beerling and Perrins 1993). A common garden experiment conducted in Denmark revealed a latitudinal pattern whereby plants from northern populations were found to have reduced above- ground biomass, basal stem diameter, and height and were able to reproduce more quickly (Kollmann and Ban˜uelos 2004). (d) Illustrations * Drawings featuring vegetative (Fig. 1) and reproductive characteristics (Fig. 2) are presented here. Numerous colour photos are available on the web, including Graham (2003).



3. Economic Importance and Environmental Impact (a) Detrimental * The invasive character of I. glandulifera is indicated by its occurrence in eight provinces since first being identified in Ottawa in 1901. Likewise, Toney et al. (1998) referred to its ‘‘continuing range expansion’’ in the northwestern United States. In British Columbia, it is spreading rapidly through the greater Vancouver area (Graham 2003; Clements unpublished observations), which features many sensitive riparian habitats important for rearing salmon. When thick patches of I. glandulifera die off in the fall, the stalks quickly rot exposing large areas of river banks and making them increasingly susceptible to erosion from high winter flows (Roblin 1994; Graham 2003; Sheppard et al. 2006). Even during the growing season, the plants offer little protection against soil erosion due to their extremely shallow root systems. The plant also occurs in damp areas away from streams, but spread seems primarily connected with its association with riparian areas (Clements, unpublished observations). Impatiens glandulifera has not been reported to infest agricultural fields, but it does invade forested areas beyond riparian zones (Clements, unpublished observations). In the Langley, BC, area, the Langley Environmental Partners Society removed 91 m3 from riparian areas between 2003 and 2006, plus an additional approximately 1 km of streambank was mowed to control I. glandulifera (Lisa Dreves, personal communication 2007). In 2006, the Comox Valley Naturalists began removing I. glandulifera from the Courtney River watershed on Vancouver Island, BC, removing 83 950 plants from the riparian area (Sellentin and Millham 2006). Rapid spread of the plant in the watershed had been noted since 2001. In southern Ontario, I. glandulifera is listed among 29 Category 1 species, i.e., ‘‘invasive species that can dominate a site to exclude all other species and remain dominant on the site indefinitely’’ where it is reported to dominate forests and wet meadows where it occurs (Urban Forest Associates 2002). It continues to increase in southern Ontario, forming monocultures more than 2 m tall under ideal conditions (Stephen Smith, Urban Forest Associates, personal communication 2007). Attempts to control I. glandulifera in the Todmorden Mills Wildflower Preserve in the Don Valley in Toronto, ON, have been partially successful (Stephen Smith, Urban Forest Associates, personal communication 2007). In Europe, I. glandulifera escaped from cultivation in the mid-19th century in the United Kingdom and is now a problematic invasive in many regions (Beerling and Perrins 1993; Wadsworth et al. 2000). Much of the research on the impact of this plant is from Europe, although it is clear that the same kind of impacts occur in North America (and to an increasing degree) (Toney et al. 1998; Urban Forest Associates 2002; Clements, unpublished observations). It is identified as a signifi-

cant invasive plant in at least 15 European countries (CABI 2004; Sheppard et al. 2006). Impatiens glandulifera is the tallest annual plant in Europe (Pysˇ ek and Prach 1995). Due to its large size and high reproductive output I. glandulifera is able to quickly dominate local vegetation and diminish conservation value at some sites (Roblin 1994). The height of the plant allows it to dominate at the expense of native tall nitrophilous (nitrogen loving) plants; I. glandulifera itself is considered nitrophilous (Hejda and Pysˇ ek 2006). In damp woodlands I. glandulifera can form dense monotypic stands which choke out all other plants (Perrins et al. 1993). By contrast, populations in its native range are considerably smaller (e.g., clusters of 3060 individual plants) and interspersed with other native vegetation (Tanner 2007). Plasticity in seed size and seed output, as well as the extended period for seed release, may increase the competititive ability of I. glandulifera in riparian habitats which are spatially and temporarily variable (Willis and Hulme 2004). Dominance of the plant along riverbanks has been reported to cause problems in stream management in the Czech Republic, Slovakia, Germany, the United Kingdom and other parts of Europe (Pysˇ ek and Prach 1995). Recent quantitative studies in Europe (Hejda and Pysˇ ek 2006; Hulme and Bremner 2006; Maskell et al. 2006) have provided a clearer picture of effects on plant communities. In a comprehensive survey of the United Kingdom, Maskell et al. (2006) found I. glandulifera to be relatively uncommon, in keeping with its specialized habitat requirements. Hulme and Bremner (2006) found that dense stands could reduce species diversity by as much as 25% at United Kingdom sites, whereas Hejda and Pysˇ ek (2006) found only a negligible affect of I. glandulifera on species diversity in the Czech Republic. Hejda and Pysˇ ek (2006) suggested that invasion of I. glandulifera did not reduce species diversity so much as change the dominance hierarchy, with I. glandulifera reducing populations of other nitrophilous annual species. The effect of the plant on community characteristics was studied at six locations using two approaches: space for time substitution approach (comparing invaded and uninvaded sites in similar habitats), and removal of the plant from experimental plots (Hejda and Pysˇ ek 2006). Removal of I. glandulifera allowed communities to recover without any significant consequences for species diversity. Hejda and Pysˇ ek (2006) thus concluded that the threat by I. glandulifera to plant diversity was not as great as formerly held. In the United Kingdom, Hulme and Bremner (2006) observed that the removal of I. glandulifera from invaded communities did increase species diversity but not necessarily native diversity as other invasive plants expanded rapidly into the territory formerly occupied by I. glandulifera. They recorded a higher proportion of non-native plants in plots where I. glandulifera was removed. As well as a local affect on diversity within plots (1 m2), Hulme and Bremner (2006)



observed a landscape level reduction in diversity, although this was not as pronounced. Chittka and Schu¨rkens (2001) claimed that the rich nectar of the plant attracted potential bee pollinators from other native plants resulting in reduced seed set and fitness among other plants. In central Europe the recorded rate of sugar production by I. glandulifera of 0.4790.12 mg h1 per flower was substantially higher than other common species visited by bumblebees (Chittka and Schu¨rkens 2001). This comparison involved only three other species; however, no other central European plant has been recorded as producing more than 0.3 mg h1 per flower and most produce less than 0.1 mg h1 (Comba et al. 1999a,b; Corbet et al. 2001). When Chittka and Schu¨rkens (2001) introduced I. glandulifera plants to areas where native plants occurred in Germany they recorded a 50% reduction in pollinator visits to the native species Stachys palustris L. Furthermore, seed set was reduced by 25% in mixed patches as compared to pure patches containing only S. palustris (Chittka and Schu¨rkens 2001). More work is needed to examine pollinator competition by I. glandulifera under a wider array of conditions, including under North American conditions. As well as its ability to compete for nectar and other resources, high rates of seed production, explosive dispersal from capsules and spread via water enable I. glandulifera to spread rapidly, particularly in riparian areas (see Sections 8 and 10). In the United Kingdom, the plant has posed further environmental restoration problems as the removal of the plant from riparian habitats was found to increase overall species diversity by allowing other non-native plants to be recruited to the area in place of I. glandulifera (Hulme and Bremner 2006). Hejda and Pysˇ ek (2006), working in the Czech Republic, also concluded that the removal of I. glandulifera served to increase species diversity. Hulme and Bremner (2006) found the recruitment rate to be four species m2, with one-third of these plants being non-native. Consequently, the removal of I. glandulifera from these sites actually served to increase the number of non-native plants in the area (Hulme and Bremner 2006). (b) Beneficial * The occurrence of I. glandulifera in native wetland plant communities has proved to be beneficial for certain bumblebee species. In the Czech Republic, Stary´ and Tkalcu (1998) classified the plant as an important source of nectar and pollen for common bumblebees such as Megabombus and Bombus spp., particularly increasing in significance later in the season when other flowers were no longer in bloom. Impatiens glanduliera does not interfere with crop pollination by bumblebees as the plants occur in riverside wetlands. Its presence in agricultural areas can be thought of as a conservational aid to crop pollinators and may enhance the ability of female bumblebees to overwinter successfully (Stary´ and Tkalcu˚ 1998).

Impatiens glandulifera attracts phytophagous insects such as aphids in Europe and North America (Beerling and Dawah 1993; Clements, unpublished observations). Although the plant supported insect diversity to some degree in wetland areas in the United Kingdom, with seven phytophagous insects recorded (see section 13b), the insect fauna was still impoverished and I. glandulifera generally results in a reduction in phytophagous insect diversity (Beerling and Dawah 1993). The typically purple-pink flowers of I. glandulifera resemble those of an orchid, and are widely considered to be pleasing and even the subject of poetry e.g., ‘‘Himalayan Balsam’’ (Stevenson 1982). Potted plants can be purchased from a number of nurseries in the United States and the seeds can also be purchased (e.g., on e-Bay). (c) Legislation * Although I. glandulifera is not currently classified as a noxious weed in British Columbia, the British Columbia Government has placed it on the Invasive Plant Alert List (British Columbia Ministry of Agriculture and Lands 2006). No other provincial or federal legislation in Canada refers to I. glandulifera. In Connecticut, it has been illegal since 2004 Oct. 01 to move, sell, purchase, transplant, cultivate, and distribute the plant according to Public Act 04-203 (Connecticut Invasive Plant Council 2004). Impatiens glandulifera is listed as a noxious weed in Washington State (Washington Administrative Code 2002). 4. Geographical Distribution In Canada, I. glandulifera is found in eight provinces: British Columbia, Manitoba, Ontario, Quebec, Nova Scotia, New Brunswick, Prince Edward Island and Newfoundland (Fig. 3). Douglas et al. (1998) reported that I. glandulifera was infrequent in the lower Fraser Valley of British Columbia. However, it is now quite common, occupying numerous riparian habitats. Although the plant is quite widespread throughout southern Ontario, populations of I. glandulifera tend to be quite localized and perhaps restricted to more urban habitats such as along the Thames River in London or St. Mary’s (Mike Oldham, personal communication) or the Don Valley in Toronto (Stephen Smith, personal communication). Similarly, I. glandulifera occurs as fairly isolated populations in the Maritimes (Fig. 3). Impatiens glandulifera has been recorded as naturalized in 10 states which somewhat mirror the Canadian distribution pattern: Washington State, Oregon, Idaho, Montana, and California in the west, and Michigan, New York, Vermont, Massachusetts, and Maine in the east (USDA 2004). It has been planted as an ornamental as far north as Alaska (USDA 2002) where it also has been reported as naturalized (AKEPIC database 2004).


408 CANADIAN JOURNAL OF PLANT SCIENCE Fig. 3. Distribution of Impatiens glandulifera in Canada. Locations based on herbarium specimens from the following herbaria (abbreviations according to Holmgren et al. 1990): ACAD, CAN, DAO, HAM, NFLD, NSPM, OAC, SASK, SFUV, TRT, UBC, UWO, UWPG, V, WAT, and WIN.



In its native range, I. glandulifera occurs throughout the northern Indian provinces from Kashmir to Garhwal and in Pakistan at altitudes generally between 2000 and 2500 m (Gupta 1989; Tanner 2007) but has been reported up to 4000 m (Polunin and Stainton 1984). Impatiens glandulifera is also widespread in riparian habitats in Europe (Wadsworth et al. 2000), particularly between the latitudes of 30 and 648N (Beerling and Perrins 1993). It has colonized the majority of mainland United Kingdom, much of Ireland, the Isles of Scilly, Shetland and Orkney (Beerling and Perrins 1993). In Wales, the plant occupies many riparian habitats, particularly in the industrial coal fields in the southern district (Gunn 1986; Beerling 1990). Impatiens glandulifera is also found in: Austria (Alps), throughout the Baltic region, the Czech Republic, French Pyrenees, Germany, Holland, Hungary, the Mediterranean region, Poland, southern Russia, Slovakia, southern Sweden, Switzerland, and the former Yugoslavia (Beerling and Perrins 1993). 5. Habitat (a) Climatic requirements * It is clear that I. glandulifera is far from reaching its potential climatic range in Canada (Fig. 3), given what is known about the plant’s ability to thrive in relatively cool climates. The northern limit of I. glandulifera in north-west Europe corresponds with a heat sum of at least 2195 degree-days at roughly 648N, the extent of its distribution in Sweden (Beerling 1993; Beerling and Perrins 1993). It has also been reported as naturalized in Alaska (AKEPIC database 2004). Fertilization of the ovule is not prevented by brief periods of cold temperatures as long as germination begins when temperatures are sufficiently warm; even if plants are growing at their upper altitudinal or northern limits (Beerling and Perrins 1993). Willis and Hulme (2002) examined the affect of temperature on the rate of invasion of I. glandulifera in the United Kingdom and found that although pods were produced at the end of the season in upland (600 m above sea level) populations that experience fewer heat units; if the growing season were slightly shorter at these sites seed output would be prevented. In Europe, plants from northern latitudes exhibited reduced growth and fecundity, both in the field and in a common garden experiment, indicating some local adaptation to higher latitudes (Kollmann and Ban˜uelos 2004). Latitude alone correlated with the differences in growth and phenology observed by Kollmann and Ban˜uelos (2004); other geographical, climatic or population traits did not explain the observed patterns. In its native range I. glandulfera has been found at altitudes up to 4000 m (Polunin and Stainton 1984). Because of its preference for moist areas, rainfall might seem to be a better predictor of I. glandulifera distribution than temperature. In the Vancouver Area, BC, which receives 1199 mm precipitation annually (Environment Canada 2007), I. glandulifera is wide-

spread, particularly in riparian areas. Even within areas with fairly low rainfall levels such as the Canadian prairies, riparian areas may be invaded by I. glandulifera. For example, I. glandulifera has recently become naturalized in the Assiniboine Forest in Winnipeg, which receives 514 mm precipitation annually (Environment Canada 2007; Bruce Ford, personal communication). Similarly, Kollmann and Ban˜uelos (2004) noted that I. glandulifera occurred at European locations with moderate (e.g., Halle-Leipzig, Germany with 519 mm annual precipitation) to heavier precipitation (e.g., Zurich, Switzerland with 1137 mm annual precipitation). Thus, sufficiently high soil moisture (Beerling and Perrins 1993) is a more stringent requirement than the annual precipitation level. (b) Substratum * Impatiens glandulifera tolerates a variety of soil textures and structures. It grows in fine and coarse alluvium, maritime shingle, free-draining mineral soils, colliery spoil and peats (Beerling and Perrins 1993) and tolerates a wide range of nutrient and soil pH values, with populations found in soil with pH as low as 3.4 (based on 70 quadrats at a depth of 10 cm) (Beerling and Perrins 1993) and in alkaline silts and calcareous riverside sands with a pH as high as 7.6 (Coombe 1956). Impatiens glandulifera has been observed to grow in soil with nitrate nitrogen values as low as 0.590.3 mg g 1 and as high as 5.591.3 mg g1 (Beerling and Perrins 1993); the latter is not an extremely high concentration (Paul Brown, personal communication) and more research is needed to evaluate its true tolerance range, especially because it is referred to as a nitrophilous species (Hejda and Pysˇ ek 2006). The plant can also tolerate a wide range of soil moisture from 15 to 53% (Beerling and Perrins 1993), but does not thrive in drier habitats and tends to be limited to moist habitats such as riparian areas, marshes and ditches (Toney et al. 1998). (c) Communities in which the species occurs * Impatiens glandulifera requires a moderately disturbed area for establishment (Sinker et al. 1985; Maskell et al. 2006). Examples of disturbances that facilitate invasion include uprooted trees, fallen branches and large scale winter flooding of river banks (Sinker et al. 1985). In its native Himalayas, I. glandulifera commonly occurs in deciduous and mixed forests up to the timberline, preferring wetter, open or slightly shaded areas with less dense grass cover (Pysˇ ek and Prach 1995). Likewise in Canada, I. glandulifera occurs along riverbanks, marshes, bogs, ditches, roadsides, and vacant lots (Clements and Feenstra, unpublished data). Within the Trinity Western University Ecosystem Study Area in Langley, BC, it often formed monotypic stands; however, smaller populations of 34 plants and individual plants also occurred occasionally, particularly in dryer areas. Species growing near the plant were: fireweed (Epilobium angustifolium L.), hairy cat’s ear



(Hypochaeris radicata L.), red alder (Alnus rubra Bong.), field bindweed (Convolvulus arvensis L.), bull thistle [Cirsium vulgare (Savi) Ten.], ox-eye daisy (Leucanthemun vulgare Lam.), common tansy (Tanacetum vulgare L.), tufted vetch (Vicia cracca L.), beaked hazelnut [Corylus cornuta var. californica (A.DC.) Sharp], common snowberry [Symphoricarpos albus (L.) Blake], sweet gale (Myrica gale L.), creeping buttercup (Ranunculus repens L.), self-heal (Prunella vulgaris L.), American winter cress (Barbarea orthoceras Ledeb.), lady fern [Athyrium filix-femina (L.) Roth.], ribwort (Plantago lanceolata L.), and the common touch-me-not (Impatiens noli-tangere) (Feenstra unpublished observation). In other Canadian regions, I. glandulifera is likewise associated with plants of riparian areas, but because of the tendency of I. glandulifera to form monotypic stands the diversity of plants within these stands is likely fairly low. Impatiens glandulifera is also associated with riparian communities in Europe (Wadsworth et al. 2000; Hejda and Pysˇ ek 2006; Hulme and Bremner 2006). The species was considered widespread in four major communities, as identified according to the National Vegetation Classification System, along the Rivers Taff and Ely in Glamorgan (United Kingdom): (1) Inundation communities: river-gravel, river alluvium and river-shingle; (2) Fens: Phragmites australis (Cav.) Trin. ex Steud. Urtica dioica L. fen: Epilobium subcommunity, also occurs at times on inundated river islands; (3) Mesotrophic grasslands: coarse grass [Arrhenatherum elatius (L.) P.Beauv.], tall herb [Myrrhis odorata (L.) Scop.], and tall herb related communities of Epilobium angustifolium L., E. hirsutum L., and Petasites hybridus (L.) P.G. Gaertn., B. Mey. & Scherb.; and (4) Woodlands: occurs below and around developing canopies of planted and mixed woodlands in early successional stages: Alnus-Fraxinus-Lysimachia woodland, Deschampsia cespitosa (L.) Beauv.; Carex remota L. subcommunity, Fraxinus-Acer campestre L. and Mercurialis woodland, Acer-Ulmus community with Sambucus nigra L. subcommunity (Beerling and Perrins 1993). The expansion of I. glandulifera beyond riparian habitats is only occasional (Pysˇ ek and Prach 1995). 6. History Impatiens glandulifera was first recorded in Canada in 1901 in Ottawa, Ontario (CAN; herbarium codes as in Holmgren et al. 1990) from a large roadside population. Its distribution has gradually expanded to include other parts of Ontario. Impatiens glandulifera first appeared in the Hamilton area in the 1950s (Rothfels 2004). There are many other Ontario herbaria records from the 1950s, but a noticeable gap subsequent to the initial records from Ottawa. By the 1950s, I. glandulifera was found growing in many parts of southern Ontario and by 1968 it had been recorded in Thunder Bay. In 1937, specimens were found in Burnaby British Columbia alongside Still Creek, near Burnaby Lake

(UBC). It is likely that the species was introduced via ship’s ballast, appearing in the port city of Victoria at about the same time (Richard Hebda, personal communication). By 1944, the species had also become established in Washington State (Toney et al. 1998). Also in 1937, plants were collected from vacant lots in New Glasgow, Nova Scotia (ACAD). The first specimen recorded in Quebec was found at Coteau-du-lac in 1940 along the Saint Lawrence River (CAN); in New Brunswick at St. John in 1943 (DAO); in Newfoundland at Conception Bay in 1970 (NFLD), and in Manitoba at Winnipeg in 1987 (WIN). Although widely grown as a garden ornamental in Manitoba, Saskatchewan and Alberta (Karen Jones, personal observation), with the exception of isolated occurrences in Winnipeg, I. glandulifera does not appear to have naturalized in the Prairie Provinces to date. The most recent new provincial record is for Prince Edward Island where a specimen was collected in New Annan in 1999 (DAO herbarium; MacQuarrie and Schaeffer 2001). Impatiens glandulifera was first introduced to the United Kingdom in 1839 as an ornamental garden plant (Perrins et al. 1993) by J. F. Royle, who worked as a surgeon in India and sent examples of I. glandulifera to the Horticultural Society of London [tcm (r&d) 2006]. In 1855, the species was recorded as a naturalized alien in Middlesex and Hertfordshire near Manchester (United Kingdom) from where it spread rapidly (Kent 1975). The spread of the plant was so rapid that it was given weed status in 1898, less than 60 yr after its introduction (Lee 1984). It was recorded to have escaped from cultivation in Litomerice, Northern Bohemia in 1896 (Pysˇ ek and Prach 1995). 7. Growth and Development (a) Morphology * The large stem base of I. glandulifera and many fleshy adventitious roots serve to anchor the plant in the soil (Ennos et al. 1993), and more adventitious roots are produced when plants are blown over, or when plants are growing on sloping terrain (Beerling and Perrins 1993). Roots are strengthened peripherally by lignification of vascular tissue (Ennos et al. 1993). At up to 3 m in height, it is a strong competitor with other species (Pysˇ ek and Prach 1995) and can project its seeds a distance of several metres (see Section 8b). (b) Perennation * Impatiens glandulifera is a summer annual reproducing by seed (Pysˇ ek and Prach 1995). (c) Physiological data * In a study by Beerling and Perrins (1993) of I. glandulifera across a wide range of habitats in the United Kingdom, stomatal density of both adaxial and abaxial surfaces of mature leaves was lower in shaded areas than in open areas. In both open and shady areas the adaxial surface had a higher density of stomata than the abaxial surface (Beerling and Perrins 1993). Stomatal density was 97912 (SE)



mm 2 on the adaxial surface, and 134913 (SE) mm 2 on the abaxial surface on plants in open areas. Stomatal density of plants in shaded areas was 82910 (SE) mm 2 on the adaxial surface and 111913 (SE) mm 2 on the abaxial surface. Beerling and Perrins (1993) demonstrated some shade tolerance of I. glandulifera through a growth analysis of plants growing in shaded and unshaded conditions, but the plant appears to be adversely affected by photon flux of B30% full daylight. The concentrations (mg g19SE) of inorganic nutrients and of inorganic compounds in stem bases and roots of plants growing in Chorlton Brook, Cumbria, Great Britain was N9.090.9, P 2.69 0.2, K 27.794.9, Ca 14.390.9, Mg3.690.3, soluble carbohydrates 2.690.9, starch 0.790.1, crude fat 1.4590.1, holocellulose 51.090.9, lignin 8.59 0.8 (Callaghan et al. 1981 cited in Beerling and Perrins 1993). The concentration of organic and inorganic compounds was found to differ in areas with contrasting amounts of sunlight (Andrews et al. 2005). Leaf and stem NO3 levels were negligible at 50100% irradiance and potassium, malate2 and sugars, respectively, accounted for 33.250.1%, 19.320.8% and 2.02.6% of total osmoticum in stems (Andrews et al. 2005). At irradiance levels of 210%, NO3 concentrations were four to eight times greater in stems than leaves; Andrews et al. (2005) concluded that these high concentrations in the stems enabled I. glandulifera to reach heights up to 3 m even at low light levels, with NO3 taking the place of other molecules such as malate or carbohydrates as an osmoticum. Lobstein et al. (2001) detected levels of naphthaquinone, a class of secondary metabolites with known allelopathic properties, in both leaf and stem tissue of I. glandulifera in France. Likewise, naphthaquinones were detected in plants collected in Langley, BC, in 2004 (Andrea Busby, unpublished data). (d) Phenology * In British Columbia, seedlings emerge in FebruaryMarch and grow rapidly; Birch (1999) recorded heights of 1015 cm by 199 Apr. 12. Flowering begins in late July and continues through October in British Columbia (Clements, unpublished observations). Seedling emergence is later in other regions of Canada with cooler temperatures in spring, but flowering times are similar. Over winter the mature plants decay almost completely, which aids in the establishment of seedlings in areas where I. glandulifera formed patches in the previous year (Clements and Feenstra, unpublished obs.) although some of the remaining material may be sufficient to prevent germination of other species (Beerling and Perrins 1993). Germination is epigeal (cotyledons are above the ground) and occurs from February to March in the United Kingdom (Beerling and Perrins 1993), in FebruaryMarch in BC (Clements, unpublished observations), but later in parts of Canada where there is

snow cover. The testa splits in the region of the radicle, which enlarges as it emerges; after 12 d, the first lateral roots emerge and the radicle begins to develop fine root hairs. The cotyledon stage follows until early April, followed by rapid shoot extension and leaf expansion from July to October. The time from germination to flowering has been measured as 13 wk in the United Kingdom and flowering continues for 12 wk (Perrins et al. 1993). In BC or Great Britain, flowering begins at the end of June and continues to either the first severe frost, or until October when the plant begins senescing (Perrins et al. 1993; Clements, unpublished data). In Denmark, it was found that flowering occurs earlier further north, likely due to shorter day length (Kollmann and Ban˜uelos 2004). Seeds are set from mid-July and onwards although there is a delay at shady sites; flowering is delayed 23 wk in such locations (Beerling and Perrins 1993). (e) Mycorrhiza * None recorded. 8. Reproduction (a) Floral biology * Impatiens glandulifera is both insect and self-pollinated (Valentine 1978). Self-pollination of the same flower is rare as the flowers are protandrous with the stamens maturing before the pistil; the anthers are shed subsequent to pollen depletion to reveal the receptive stigma and the female stage only lasts a few hours (Valentine 1971). Pollination of one flower by another flower on the same plant (i.e., geitonogamy) frequently occurs (Valentine 1971), but I. glandulifera is not cleistogamous (self-pollinating via unopened flowers) (Beerling and Perrins 1993). The abundant nectar produced by I. glandulifera (Barrow and Pickard 1984) attracts numerous pollinators including many types of bumblebees (Bombus spp.), honeybees (Apis mellifera L.), wasps and moths (Dunn 1977; Barrow and Pickard 1984; Fussell and Corbet 1992). The pollination ecology of I. glandulifera has been studied extensively (e.g., Daumann 1967; Dunn 1977; Valentine 1971, 1978; Bu´rquez and Corbet 1991; Chittka and Schu¨rkens 2001). Its flowers are welldesigned for pollination by bumblebees in that the corolla tends to enclose the bumblebee completely, resulting in a thorough dusting of pollen and leading to high percentages of fertilized ovules (Proctor and Yeo 1973; Beerling and Perrins 1993). As mentioned in section 3a, the relatively high nectar production by I. glandulifera has been linked to its invasive success in Europe. (b) Seed production and dispersal * Although a single plant is capable of producing up to 2500 seeds (Koenies and Glavac 1979; Pysˇ ek and Prach 1995), seed production varies depending on the environment. Salisbury (1961) observed up to 800 seeds plant 1 produced at densities of 20 plants m 2, but 1600 seeds plant 1 may be produced with lower plant densities or in more



favorable environments (Koenies and Glavac 1979; Perrins et al. 1993). Willis and Hulme (2004) found that taller plants produced proportionally more pods and more seeds per pod, ranging from 1 to 19 and averaging 7.0 per pod for lateral infloresences and 8.5 for terminal inflorescences. Number of pods per plant was one of the most variable traits, with some plants bearing 100 pods plant 1 (Willis and Hulme 2004). Kollmann and Ban˜uelos (2004) measured seed weights of 10.819.1 mg per seed. A field study in the United Kingdom noted that I. glandulifera produced fewer seeds at higher elevations though the plant was able to germinate in areas above its current altitudinal distribution (Willis and Hulme 2002). In another study, Willis and Hulme (2004) observed a negative correlation between seed size and heat units experienced over the growing season. Capsules split explosively when touched (Gilkey and Dennis 2001) and release seeds as far as 5 m from the parent plant (Beerling and Perrins 1993), although the modal distance was recorded approximately 1 m in a BC study (Birch 1999) and 2 m in a study done in the United Kingdom (Beerling and Perrins 1993). The long distance transport of seeds is facilitated by human agency and by water dispersal; seeds travel near the channel bottom and are deposited on the river banks only during heavy floods (Pysˇ ek and Prach 1995). It is likely that animals also transport the seeds (Pysˇ ek and Prach 1995). (c) Viability of seeds and germination * Seeds require chilling and germinate in the spring (Barton 1939; Pysˇ ek and Prach 1995). Impatiens glandulifera is not known to produce a sizeable persistent seed bank (Grime et al. 1988; Sheppard et al. 2006). A study done in British Columbia detected no evidence of a persistent seed bank in areas where high densities of I. glandulifera occurred (Burns and Clements, unpublished data). However, it has been reported that some seeds may persist beyond a single year and it is generally recommended that control measures be repeated for several years at a given location (King County Department of Natural Resources 2005; Stephen Smith, personal communication 2007; Lisa Dreves, personal communication 2007; Washington State Noxious Weed Control Board 2007). In its native range, breaking of dormancy is dependent on abrupt seasonal temperature changes (Mumford 1988). Survival of the seed was not related to winter temperature or the number of days below freezing (Willis and Hulme 2002). In the laboratory, dormancy can be broken by maintaining imbibed seeds at 48C; the period of chilling required decreased with increased seed age (Mumford 1988). If the stratification requirement is not met, fully imbibed seeds can remain dormant for several years at 208C and the breaking of dormancy in the seeds can be identified by the presence of anthocyanin in the cells of the root cap (Mumford 1989). Interrupting the stratification with desiccation did not have an effect on

the required chilling period, however an interruption of the stratification at 48C with a period at 208C was found to increase the required chilling period. (d) Vegetative reproduction * No vegetative reproduction is reported (Pysˇ ek and Prach 1995). 9. Hybrids There are no recorded hybrids involving I. glandulifera. 10. Population Dynamics Impatiens glandulifera commonly forms dense monotypic stands. In the last decade, I. glandulifera populations have expanded throughout greater Vancouver, BC, along riparian corridors (Clements, unpublished observations) but this spread has not been quantified for this or any other region in Canada. According to Beerling and Perrins (1993) reemergence and monotypic stands in the United Kingdom may be helped by the hollow woody stems that often persist through the winter and into the spring; this helps to prevent other species from invading territory occupied by I. glandulifera. In addition, synchronous germination of seeds helps to form monotypic stands wherein all the plants are the same age. Initial seedling density and final flowering density were not strongly correlated in wild populations studied in the United Kingdom, but a slight increase in seedling survivorship was seen at higher initial seedling densities (Prowse 1998). The same study found that mortality peaked in late May and early June. Plants from shaded sites had a higher maximum biomass likely due to increased leaf area ratio, but plants from open areas had a higher maximum relative growth rate (Beerling and Perrins 1993). The increased concentration of nitrate in plants from shaded sites gives the plants a competitive advantage and allows them to reach great heights (Andrews et al. 2005). At the landscape level, riparian areas become increasingly occupied by I. glandulifera due to efficient seed dispersal, including transport via watercourses (Pysˇ ek and Prach 1995; see Section 8b). The rate of spread of I. glandulifera has been quantified in a number of studies, and generally it is ranked as having one of the highest rates of spread among invasive species. For example, Pysˇ ek and Prach (1993) found it spread more rapidly in comparison to giant hogweed (Heracleum mantegazzianum Somm. et Lev.), a monocarpic perennial (i.e., dies after the 1st season), and two polycarpic perennials (i.e., producing seeds in multiple years), Japanese knotweed [Fallopia japonica (Houtt.) Ronse Decr.] and giant knotweed [Fallopia sachalinensis (F. Schmidt) Ronse Decr.]. By analyzing logistic growth curves of its spread through the United Kingdom, Perrins et al. (1993) determined that I. glandulifera obtained a maximum spreading rate of 38 km yr 1 (estimated to have occurred in about 1933 in the later stages of the invasion process). The maximum for I. parviflora was 24 and that for I. capensis was 13 km



yr 1. Usher (1986) estimated that I. glandlifera spread 35 km yr l over an interval of 20 yr in the United Kingdom. At an individual plant level, spread is limited to 2 m yr 1 due to ballistic and animal dispersal (Perrins et al. 1993). Pysˇ ek and Hulme (2005) summarized the measured rates of spread of the plant in various European locations as follows: United Kingdom (various regions) at 2.63.9 m yr 1 (Perrins et al. 1993; Williamson et al. 2003); Czech Republic at 3.7 m yr 1 (Williamson et al. 2003). These rates of spread calculated from sampling grids and floristic records may be underestimates, however, as they are not sufficient to account for how rapidly I. glandulifera spread throughout parts of the United Kingdom (Collingham et al. 1997; Pysˇ ek and Hulme 2005). 11. Response to Herbicides and Other Chemicals A common chemical control method for I. glandulifera is glyphosate applied twice a season prior to flowering (Wadsworth et al. 2000). Due to the riparian location of many populations, the choice of herbicides and method of application are limited and application is often not advised. Typically, upstream populations are best managed first because of seed transport downstream (Pysˇ ek and Prach 1995). Wadsworth et al. (2000) found that 99% control was almost as ineffective as no control at all due to prolific seed production. Control has also been achieved by spraying 2,4-D amine at rates of 69 L ha 1 early on in the season before flowering to prevent the development of seeds; plants sprayed while flowering were able to produce viable seed (Beerling and Perrins 1993). Typically, 2,4-D amine needs to be applied twice, with the first application early in the season (Beerling and Perrins 1993). 12. Response to Other Human Manipulations Cutting plants at the base of the stem potentially reduces flowering and simultaneously prevents disturbance of the soil. A trial in Langley, BC, demonstrated that plants cut in August were still able to reestablish from the root system and flower, and thus able to produce seed in the fall (Snidal and Clements, unpublished observations). The moist, riparian habitat favored by I. glandulifera facilitates this recovery by cut plants. The root system is relatively shallow (i.e., 1020 cm), and thus pulling does not disturb the soil as much as with more deeply rooted plants. Thus, for the same effort, it may be worthwhile to uproot the plants to prevent seed production. Plants can be composted on site within a week or so as long as seed capsules are not present (King County Department of Natural Resources 2005). More extensive trials need to be conducted, but manual removal of plants does seem to be effective (although costly and requiring extensive person power) in the British Columbia context. A Comox Valley Naturalist crew was able to remove over 80 000 I. glandulifera plants in the Comox Valley on Vancouver Island in 2006, which involved 15 d of work (Sellentin and

Millham 2006). Although the Langley Environmental Partners Society has employed pulling and cutting, the most efficient method attempted to date is mowing mid to late July, immediately following the appearance of blossoms (Lisa Dreves, personal communication). Another technique that has recently been attempted in the Fraser Valley is flaming, using a small portable propane flamer prior to flowering. However, it appeared that some plants either recovered or escaped control, because quite a number of plants were seen flowering in the same location later in the season (Feenstra and Clements, unpublished observations). As discussed in Section 3, it is imperative that management of I. glandulifera account for potential negative community changes following removal, including invasion by other non-native species (Hulme and Bremner 2006). 13. Response to Herbivory, Disease, and Higher Plant Parasites (a) Herbivory (i) Mammals * In the United Kingdom, sheep and cattle graze the leaves, stems and flowers equally (Beerling and Perrins 1993). (ii) Insects * No published information is available on herbivory of I. glandulifera in North America, but preliminary observations suggest that the plant is not host to a large diversity of insects (Clements, unpublished obs.). Beerling and Dawah (1993) recorded relatively few phytophagous insects on the foliage of I. glandulifera in Cardiff, United Kingdom. These included: Hemiptera-Aphididae, Cicadellidae, and Nabiidae. Coleoptera-Curculionidae, and Chrysomelidae, Diptera- Agromyzidae, Lepidoptera- Sphingidae. The Lepidopteran Deilephila elpenor L. is known to feed on the plant in the United Kingdom (Allen 1949). Two specific aphid species were recorded from I. glandulifera: Aphis fabae Scopoli and Impatientinum balsamines Kallenbach (Gilbert and Pearman 1988 cited in Beerling and Perrins 1993). Sheppard et al. (2006) listed I. glandulifera as one of the top 20 environmental weeds as potential biological control targets in Europe, but noted that no attempts had been made to utilize biological control for this species. As of April 2006, CABI scientists began a program to investigate possibilities for using biological control against I. glandulifera in Europe (Tanner 2007). A team collected numerous arthropods from I. glandulifera in Pakistan and noted extensive arthropod damage to plants in the field; the flea beetle Altica himensis Shukla was rejected as a potential biocontrol agent, while the thrips Taeniothrips major Bagnall was assigned to further testing (Tanner 2007). (b) Diseases (i) Fungi * Hymenoscyphus vitellinus (Rehm) Kuntze was recorded as occurring on I. glandulifera in the United Kingdom (Dennis 1986; Farr et al. n.d.). Glushakova



and Chernov (2005) recorded that epiphytic yeasts occurred on I. glandulifera. In Germany, Phyllosticta impatientis (L. A. Kirchn.) Fautrey and Ascochyta weissiana Allesch. were found on the leaves of I. glandulifera (Farr et al. n.d.). A rust tentatively identified as Puccinnia argentata (C. F. Schulz) Wint. was found on I. glandulifera in its native Pakistan in 2006 (Tanner 2007). This rust was already known to occur on I. nolitangere and I. capensis, signifying that the rust found in Pakistan was either a different species or a different pathotype of P. argentata. Tanner (2007) evaluated this pathogen as having good potential for biocontrol use in Europe. The CABI scientists also identified leafspot damage in Pakistan due to three Coelomycetes species (Phomopsis sp., Phoma sp. and Ascochyta sp.), a downy mildew (Peronosporaceae) and a powdery mildew (Erysiphaceae) (Tanner 2007). Erysiphe communis Wallr. ex Fr. and Oidium spp. have also been reported on I. glandulifera in India (Farr et al. n.d.). (ii) Bacteria * None recorded. (iii) Viruses * None recorded. (c) Higher Plant Parasites * None recorded 14. Prognosis Impatiens glandulifera has been found in Canada for over 100 years and to some degree the invasion has been gradual and unnoticed. However, in some areas, particularly within British Columbia and Ontario, it has spread fairly widely and is well established and has become the target of large scale removal campaigns starting in the 1990s. Within 16 years of its introduction into the United Kingdom (18391855), it was able to spread from gardens and become established (Beerling and Perrins 1993). Now it is a widespread problem throughout Europe. Periodic but unsystematic efforts at managing populations in the Czech Republic have allowed re-invasion to occur repeatedly (Wadsworth et al. 2000). The climate and topography of the coastal region of southwestern British Columbia is similar to that of many locations throughout Europe. The average rainfall in this region of British Columbia is greater than that of the United Kingdom. Preferring wetter habitats, I. glandulifera abounds in this area due to extensive watersheds. In other Canadian locations with similar climates to southwestern British Columbia and extensive riparian areas, particularly the Maritimes and parts of southern Ontario and where it is already established, it could potentially become more widespread. Impatiens glandulifera is able to outgrow its competitors as it reaches great heights in a short period of time and thereby shades other plants that are living in the close vicinity. The prolific seed production and explosive seed dehiscence contribute to its invasive potential. Spread is also facilitated by waterways and human transportation.

Although glyphosate can be used to control I. glandulifera, its use is limited as the plants are often near water ways where herbicide use is not recommended. One alternate method of treatment is uprooting the plant, which is relatively easy due to its shallow rooting. In addition, the plants could be cut back or mowed before flowering. Flaming also shows some promise as a control technique. These methods, however, are time consuming, and could be quite costly. The recent efforts to develop biological control in Europe (Tanner 2007) could eventually provide additional measures to be used against I. glandulfera in North America. As described in Section 3, recent studies in Europe have highlighted potential negative effects of the removal of I. glandulifera. Consequently, I. glandulifera removal should be managed synchronously with nonnative control measures and ideally be accompanied by planting native species to ensure the restoration of native species composition. The prognosis for curbing the spread of I. glandulifera in Canada seems quite poor. It has rapidly established itself along waterways in many regions, following the pattern seen over the past two centuries in Europe.

ACKNOWLEDGEMENTS We thank numerous individuals who have contributed insights on I. glandulifera in Canada, particularly Beverly Birch, Leanne Burns, Andrea Busby, and Tonya Snidal of Trinity Western University, Lisa Dreves (Langley Environmental Partners Society), Bruce Ford University of Manitoba), Richard Hebda (Royal BC Museum), Michael Oldham (Ontario Ministry of Natural Resources), Carl Rothfels (Royal Botanical Gardens, Hamilton, ON), Stephen Smith (Urban Forestry Associates, Toronto, ON), and Ernie Sellentin (Comox Valley Naturalists, BC). Logistical and financial support for the research was provided by Trinity Western University and the University of Winnipeg. We also gratefully acknowledge the herbaria which have lent specimens examined and supplied information during the course of the study, and the UBC herbarium in particular for providing space for examining loans from some of the other herbaria. Suzanne Warwick and several anonymous reviewers provided excellent assistance in improving the paper. AKEPIC database 2004. Non-native plants of Alaska. [Online]. Available: http://akweeds.uaa.alaska.edu [2007 Sep. 29]. Allen, P. B. M. 1949. Larval food plants. Watkins & Doncaster, London, UK. 126 pp. Andrews, M., Maule, H. G., Raven, J. A. and Mistry, A. 2005. Extension growth of Impatiens glandulifera at low irradiance: Importance of nitrate and potassium accumulation. Ann. Bot. 95: 641648. Barrow, D. A. and Pickard, R. S. 1984. Size-related selection of food plants by bumblebees. Ecol. Entomol. 9: 369373.


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