Cynoglossum officinale (hound's tongue)
- 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 Vectors
- Plant Trade
- Impact Summary
- 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
- Cynoglossum officinale L.
Preferred Common Name
- hound's tongue
International Common Names
- English: begger's lice; common bur; common houndstongue; dog burr; dog's tongue; glovewort; houndstongue; woolmat
- Spanish: lengua de perro comun
- French: cynoglosse officinale; herbe d'antal; langue de chien; langue-de-chien
Local Common Names
- Germany: Echte Hundszunge; Gemeine Hundszunge
- Italy: cinoglossa
- Netherlands: hondstong
- Sweden: hundtunga
- CYWOF (Cynoglossum officinale)
Summary of InvasivenessTop of page C. officinale, native to Eurasia, is a highly invasive weed now present throughout much of North America, probably introduced as a seed contaminant. It is a common weed of rangeland and spreads locally attached to the fur of livestock. Its presence reduces the availability of forage grasses and it is poisonous to livestock if ingested. It is possible that further introductions may occur to other countries with similar climates.
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Plantae
- Phylum: Spermatophyta
- Subphylum: Angiospermae
- Class: Dicotyledonae
- Order: Boraginales
- Family: Boraginaceae
- Genus: Cynoglossum
- Species: Cynoglossum officinale
Notes on Taxonomy and NomenclatureTop of page Cynoglossum officinale is the accepted scientific name of this weed and no subspecies have been reported. The genus Cynoglossum belongs to family Boraginaceae (Borage family). The common name in English is 'hound's tongue', derived from the shape of the leaves, though it also known by a variety of other names (Macoun, 1884; Clark and Fletcher, 1909; Cockayne, 1961; Greatorex, 1966; Scoggan, 1978; Muenscher, 1980).
DescriptionTop of page C. officinale is a herbaceous weed, producing either single or multiple erect hairy stems, 0.3 to 1.2 m tall and a thick, woody taproot. It has rough, hairy, alternate leaves, 10-30 cm long and 2-5 cm wide, lanceolate to oblong, i.e. shaped like hound's tongue (Upadhyaya et al., 1988). Lower leaves with short petioles and in rosettes. Upper leaves clasp the stem. Leaf margins are entire. The flowers are dull reddish-purple in colour, with five petals, and are present in axils of upper leaves. The inflorescence is a raceme. Indehiscent burred fruits, which are brown to greyish-brown in colour, consist of four nutlets. The seed coat is dark brown to black with a white embryo inside.
Plant TypeTop of page Biennial
DistributionTop of page C. officinale has a broad native range in the temperate zones from western Europe (Tutin et al., 1972) to central Asia (USDA-ARS, 2003), and has been introduced to the USA (Cochrane, 1975; Dickerson and Fay, 1982; Knight et al., 1984), and Canada (Breitung, 1957a, b; Boivin, 1966; Scoggan, 1978).
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|
|Georgia (Republic of)||Present||Native||USDA-ARS, 2003|
|Canada||Present||Present based on regional distribution.|
|-Alberta||Present||Introduced||Invasive||Upadhyaya et al., 1988; Upadhyaya and Cranston, 1991|
|-British Columbia||Present||Introduced||1922||Invasive||Anon., 2002a; Taylor and MacBryde, 1977|
|-Manitoba||Present, few occurrences||Introduced||Upadhyaya et al., 1988; Upadhyaya and Cranston, 1991|
|-Newfoundland and Labrador||Absent, intercepted only||Introduced||Not invasive||Upadhyaya et al., 1988; Upadhyaya and Cranston, 1991|
|-Ontario||Present||Introduced||before 1859||Invasive||Macoun, 1884; Upadhyaya et al., 1988|
|-Prince Edward Island||Absent, intercepted only||Introduced||Not invasive||Upadhyaya et al., 1988; Upadhyaya and Cranston, 1991|
|-Saskatchewan||Present, few occurrences||Introduced||Upadhyaya et al., 1988|
|USA||Present||Present based on regional distribution.|
|-New Hampshire||Present||Introduced||USDA-NRCS, 2002|
|-New Jersey||Present||Introduced||USDA-NRCS, 2002|
|-New Mexico||Present||Introduced||USDA-NRCS, 2002|
|-New York||Present||Introduced||USDA-NRCS, 2002|
|-North Carolina||Present||Introduced||USDA-NRCS, 2002|
|-North Dakota||Present||Introduced||USDA-NRCS, 2002|
|-Rhode Island||Present||Introduced||USDA-NRCS, 2002|
|-South Dakota||Present||Introduced||Invasive||USDA-NRCS, 2002|
|-West Virginia||Present||Introduced||USDA-NRCS, 2002|
|Czech Republic||Present||Native||USDA-ARS, 2003|
|Iceland||Present||Love and Love, 1956|
|Netherlands||Present||Native||Freijsen et al., 1980|
|Poland||Present||Native||Skalinska et al., 1959|
|Russian Federation||Present||Present based on regional distribution.|
|-Central Russia||Present||Native||USDA-ARS, 2003|
|-Eastern Siberia||Present||Native||USDA-ARS, 2003|
|-Northern Russia||Present||Native||USDA-ARS, 2003|
|-Southern Russia||Present||Native||USDA-ARS, 2003|
|-Western Siberia||Present||Native||USDA-ARS, 2003|
|Yugoslavia (Serbia and Montenegro)||Present||Native||USDA-ARS, 2003|
History of Introduction and SpreadTop of page C. officinale is considered native to Eurasia (Scoggan, 1978). It was probably introduced to North America as a contaminantion of cereal seeds (Knight et al., 1984). It was reported as common around Montreal, Quebec, and present in Ontario, Canada, as early as the 1880s (Macoun, 1884), with herbarium specimens collected in Ontario in 1859 and in western Canada in 1922 (Upadhyaya et al., 1988) indicating its spread. It was already reported as a troublesome weed in Canada before 1910 (Clarke and Fletcher, 1909).
Risk of IntroductionTop of page There is a high risk of further introduction of C. officinale to other countries with similar temperate climates as a contaminant of seed, wool or other livestock products. It is on the noxious weed lists for seven states of the USA (USDA-NRCS, 2002).
HabitatTop of page C. officinale is a weed of temperate regions. It is found in rangelands, pastures, roadsides and waste places, and abandoned croplands (Alex and Switzer, 1976; Scoggan, 1978; Dickerson and Fay, 1982). It has been reported to occur in eastern North America on gravelly, somewhat limey soils (Meunscher, 1980), in the UK in sandy areas (Cockayne, 1961) and in old dune-grassland with dry sandy soils (Boorman, 1982), in the Netherlands on calcareous costal dunes, with high soil nitrogen (Freijsen et al., 1980) and in eastern Canada on rocky pastures in limestone regions (Frankton and Mulligan, 1970). Clapham et al. (1962) reported its occurrence in grassy places and borders of woods on dry soils, on gravel, sand, limestone, or chalk, near the sea. In British Columbia, Canada, it occurs on disturbed sites of the interior Douglas fir (Pseudotsuga menziesii) and ponderosa pine (Pinus ponderosa)-bunchgrass biogeoclimatic zones (Taylor and McBryde, 1977). These zones have cold winters and hot dry summers. It is also found in many clear-cut logged areas (Cranston and Pethybridge, 1986) and grows in grasslands and low- to mid-elevation forests in British Columbia, Canada (Anon., 2002b).
Habitat ListTop of page
|Terrestrial – Managed||Managed forests, plantations and orchards||Present, no further details||Harmful (pest or invasive)|
|Managed grasslands (grazing systems)||Present, no further details||Harmful (pest or invasive)|
|Disturbed areas||Present, no further details||Harmful (pest or invasive)|
|Rail / roadsides||Present, no further details||Harmful (pest or invasive)|
|Terrestrial ‑ Natural / Semi-natural||Natural grasslands||Present, no further details||Harmful (pest or invasive)|
|Coastal areas||Present, no further details|
Hosts/Species AffectedTop of page C. officinale is mainly a weed of grasslands, also forests, but can also be a problem in cultivated crops,
Biology and EcologyTop of page Genetics
The diploid chromosome number of 2n=24 has been reported in C. officinale plants obtained from Ontario, Canada (Mulligan, 1957), Belgium, Denmark, the USA (Britton, 1951), Iceland (Love and Love, 1956), and Poland (Skalinska et al., 1959).
Physiology and Phenology
C. officinale is generally considered a biennial or short-lived perennial. Seedlings emerge in both spring and autumn and the rosettes bolt in the second year. Its deep root system gives it a competitive advantage over grasses under conditions of moisture stress. The C. officinale leaf surface is covered with uniseriate trichomes (hairs), which become more abundant as light intensity declines (Upadhyaya and Furness, 1994) and ultraviolet-B radiation levels above ambient have been reported to reduce C. officinale leaf area, leaf, stem and root biomass, and influence trichome abundance (Furness et al., 1999). Nitrogen has been shown to increase germination of C. officinale seeds (Freijsen et al., 1980). Svensson and Wigren (1982) showed application of fertilizer increased C. officinale dry biomass and second-year flowering by more than 100 and 50%, respectively, and also the number of flowers per plant.
C. officinale reproduces by seeds, with mature plants producing 2000-4000 seeds (Powell et al., 1994). Seeds attached to the mother plant can remain viable for 2-3 years (Anon., 2002b) whereas buried seeds rarely remain viable for more than one year. Viability of freshly-harvested mature seeds may exceed 90% (Boorman and Fuller, 1984). C. officinale mortality has been estimated to be 75% from seed to seedlings, 77% from seedlings to rosettes, and 94% from rosettes to flowering (Boorman and Fuller, 1984). Less than 1% of C. officinale seeds survive to produce seeds, and the high seedling mortality was suggested to be due to moisture deficits early in the summer prior to deep root penetration. Repeated flowering has been reported to occur in some C. officinale plants in the second, third and even fourth year (Boorman and Fuller, 1984), suggesting that this weed is not strictly monocarpic. In the majority of cases, however, plants die after flowering. C. officinale flowers are perfect (Taylor and MacBryde, 1977) and seed production is via autogamy. Pollination does not require insects and outcrossing or vivipary have not been reported (Upadhyaya et al., 1988). The weed relies on innate, non-embryogenic seed dormancy for its persistence; impermeability of seed coats to oxygen has been suggested as the underlying mechanism of dormancy (Qi et al., 1993; Stabell, et al., 1998). C. officinale seeds contain a high level of phenolic substances and polyphenol oxidase activity and phenolics in C. officinale seeds exert an allelopathic influence on neighbouring species. Decoated seed leachate significantly inhibits seed germination and seedling growth of several species associated with C. officinale in nature.
In Ontario, Canada, C. officinale infested regions have 770-1020 mm annual precipitation, 3.9-10.9°C mean January temperature and 19.2-22.2°C mean July temperature (Anon., 1982). Elsewhere in Canada, C. officinale inhabits zones with hot, dry summers and cold winters. C. officinale is common in areas with sandy and/or alkaline calcareous soils of variable fertility, also on gravelly and rocky sites. In Canada, C. officinale is associated with soils of Burnisolic, Luvisolic and Chernozemic orders in Alberta (Lodge et al., 1971) and is found on Eutric and Dystric Brunisolic, brown and dark brown Chernozemic and Luvisolic soils in British Columbia (Cranston and Pethybridge, 1986).
In British Columbia, Canada, C. officinale occurs mainly in the interior Douglas fir (Pseudotsuga menziesii) and ponderosa pine (Pinus ponderosa)-bunchgrass biogeoclimatic zones (Taylor and MacBryde, 1977).
Soil TolerancesTop of page
Natural enemiesTop of page
|Natural enemy||Type||Life stages||Specificity||References||Biological control in||Biological control on|
|Ceutorhynchus cruciger||Herbivore||British Columbia|
Notes on Natural EnemiesTop of page The insects Ceutorhynchus crucifer (Schroder, 1976) and C. trisignatus (Coleoptera) (Kallweit, 1977) have been recorded on C. officinale, as well as the fungal pathogens Botrytis cinerea and Erysiphe cichoracearum (Shaw, 1973), though their specificity and effects are not known. Two further insects Mogulones cruciger and Longitarsus quadriguttatus (Anon., 2002b) and two other fungal pathogens Erysiphe cynoglossi (Clerck-Floate, 1999; Clerck-Floate and Schwarzlander, 2002) and Phoma pomorum (Anon., 2002b) have been investigated as potential biological control agents.
Means of Movement and DispersalTop of page Natural Dispersal (Non-Biotic)
C. officinale nutlets remain attached to the mother plant after maturation for up to 3 years or more, forming an aerial seed bank. These seeds, however, do not disperse long distances naturally unless attached to animal fur, with Boorman and Fuller (1984) reporting that over 75% of C. officinale seeds fall within 1.2 m of the mother plants. A study in the Netherlands reported that most viable C. officinale seeds occur within the top 1 cm of the soil profile and seeds were not found at soil depths greater than 5 cm.
Vector Transmission (Biotic)
Nutlets disperse by attaching to the fur of animals, mostly cattle and sheep, grazing in infested areas (Upadhyaya et al., 1988; Upadhyaya and Cranston, 1991; Clerck-Floate, 1997).
C. officinale seeds can also disperse as contaminants of crop seeds or soil, and the weed was probably introduced to North America as a contaminant in cereal seeds (Knight et al., 1984). It may also be transported internationally in wool or animal fur, or even attached to live introduced stock (Upadhyaya et al., 1988).
Plant TradeTop of page
|Plant parts not known to carry the pest in trade/transport|
|True seeds (inc. grain)|
Impact SummaryTop of page
|Fisheries / aquaculture||None|
ImpactTop of page Due to its robust growth habit and deep root system, C. officinale reduces rangeland forage yield by competing for resources. It also interferes with establishment of desirable forage grasses, thereby decreasing forage availability for grazing and C. officinale itself is not a desirable food for animals. The barbed fruits of C. officinale attach to animal fur (Gains and Swan, 1972) which reduces their market value and may increase veterinary costs (Upadhyaya et al., 1988).
C. officinale is also a poisonous weed (Greatorex, 1966; Mandryka, 1979; Bartik and Piskac, 1981; Knight et al., 1984), with sheep being less susceptible than cattle or horses (Anon., 2002b). Its leaves contain the toxic alkaloids, echinatine, heliosupine and acetylheliosupine which are poisonous to animals when ingested (McGaw and Woolley, 1979; Resch and Mienwald, 1982; Knight et al., 1984); the concentration of these alkaloids is highest in rosette leaves. Fortunately, grazing animals will avoid browsing this species where alternative forage is available, but poisoning may occur when animals are fed hay contaminated with C. officinale leaves.
Threatened SpeciesTop of page
Social ImpactTop of page C. officinale has been reported to cause dermatitis when handled (Muenscher, 1939; Taylor and MacBryde, 1977).
Risk and Impact FactorsTop of page Invasiveness
- Proved invasive outside its native range
- Highly adaptable to different environments
- Highly mobile locally
- Has high reproductive potential
- Has propagules that can remain viable for more than one year
- Negatively impacts agriculture
- Negatively impacts human health
- Negatively impacts animal health
- Negatively impacts tourism
- Reduced amenity values
- Competition - monopolizing resources
- Produces spines, thorns or burrs
- Highly likely to be transported internationally accidentally
- Difficult/costly to control
UsesTop of page Root extracts of C. officinale have been reported to cure fever and chest and respiratory ailments (Cockayne, 1961; Altschul, 1973). Leaves of C. officinale have also been used as a mole repellent in gardens and for protection of stored vegetables and fruits from rodents (Bocs, 1983).
Uses ListTop of page
Similarities to Other Species/ConditionsTop of page C. officinale rosettes can be confused with blueweed (Echium vulgare) but the latter is separable by its narrow, more harshly hairy rosette leaves and conspicuous blue flowers (Frankton and Mulligan, 1970) as compared to the reddish-purple flowers of C. officinale. It may also be confused with common mullein (Verbascum thapsus) though this species has rosette leaves that are more hairy and have less conspicuous venation than the rosette leaves of C. officinale.
Prevention and ControlTop of page Cultural Control
Svensson and Wigren (1982) reported that inter-specific competition significantly reduced dry biomass of first- and second-year C. officinale plants as well as seed production. Dispersal of nutlets by animals, humans, vehicles and equipment should be avoided (Anon., 2002b).
For small C. officinale populations and before seeds are formed, control by hand pulling is possible (Anon., 2002b). Cutting of young rosettes below the crown in autumn or early spring, mowing of flowering stems close to the ground, and ploughing followed by cultivation have been shown to control C. officinale (Muenscher, 1980). Dickerson and Fay (1982) showed that clipping of second-year plants during flowering reduced seed production significantly and seed production of plants that resumed growth declined dramatically; however, removal of leaves from second year plants neither affected seed number nor seed weight (Boorman and Fuller, 1984).
Picloram, dicamba, chlorsulfuron (Cranston and Ralph, 1983; Cranston et al., 1983; Cranston and Pethybridge, 1986; Cranston and Wood, 1986) and 2,4-D amine (Dickerson and Fay, 1982) have been reported to effectively control C. officinale (Upadhyaya et al., 1988). In Montana, USA, seed production of second year C. officinale plants was most affected by 2,4-D when it was applied to plants 28 cm high (Dickerson and Fay, 1982), whereas chlorsulfuron provided complete control from the beginning of the rosette state until the bolted plants were 28 cm tall (Dickerson and Fay, 1982).
There are attempts to identify insects and pathogens for the biological control of C. officinale (Conner et al., 2000). Erysiphe cynoglossi, a powdery mildew fungus that is commonly found occurring on C. officinale, has been suggested as a potential biological control agent for this weed in North America (Clerck-Floate, 1999). The fungus, with characteristic white or grey velvety mycelium growth, is seen on all above-ground parts of C. officinale plants under field conditions. The fungus has been reported to reduce C. officinale root crown diameter, biomass, nutlet number, nutlet size, seed set and seed germination (Clerck-Floate, 1999) and the potential for use in biocontrol of C. officinale in North America is currently being investigated (Clerck-Floate, 1999, Clerck-Floate and Schwarzlander, 2002). A weevil, Mogulones cruciger, and a beetle, Longitarsus quadriguttatus, have also been studied for biocontrol of C. officinale (Anon., 2002b), both attacking the roots. M. cruciger was released in British Columbia, Canada, in 1998 and has shown promising results (Anon., 2002b). Phoma pomorum, an indigenous pathogen which causes brown lesions on the leaves has also been investigated (Anon., 2002b).
ReferencesTop of page
Alex JF, Switzer CM, 1977. Ontario Weeds. Descriptions, Illustrations and Keys to their Identification. Ontario, Canada: Ministry of Agriculture and Food College, University of Guelph, Publication 505:200 pp.
Altschul S, 1973. Drugs and Foods from Little-known Plants. Cambridge, USA: Harvard University Press.
Anon., 1982. Canadian climate normals, temperature and precipitation, Ontario (1951-1980). Environment Canada, Atmospheric Environment Service, Government of Canada, 254 pp.
Anon., 2002. Guide to Weeds in British Columbia. Canada: British Columbia Ministry of Agriculture, Food and Fisheries Publication, 195 pp.
Anon., 2002. Seven Steps to Managing your Weeds. A Manual for Integrated Weed Management in British Columbia, Canada. British Columbia Ministry of Agriculture, Food and Fisheries Publication, 58 pp.
Bartic M, Piskac A, 1981. Veterinary Toxicology. Amsterdam, the Netherlands: Elsevier Scientific Publication Company.
Bocs A, 1983. Cynoglossum officinale against moles and rodents. Kerteszet es Szoleszet, 32:13.
Boivin B, 1966. Enumeration des plantes du Canada. IV. Herbidées, 2 partie: Connatae Nat. Can., 93:989-1063.
Boorman LA, 1982. Some plant growth patterns in relation to the sand dune habitat. Journal of Ecology, 70:607-614.
Boorman LA, Fuller RM, 1984. The comparative ecology of two sand dune biennials: Lactuca virosa L. and Cynoglossum officinale L. New Phytologist, 96:609-629.
Breitung AJ, 1957. Annonated catalogue of the vascular flora of Saskatchewan. American Midland Naturalist, 58:58-72.
Breitung AJ, 1957. Plants of Waterton Lakes National Park, Alberta. Canadian Field Naturalist, 71:39-71.
Britton DM, 1951. Cytogenetic studies on the Boraginaceae. Brittonia, 7:233-266.
Clapham AR, Tutin TG, Warburg EF, 1962. Flora of the British Isles. Second edition. Cambridge, UK: Cambridge University Press.
Clark GH, Fletcher J, 1909. Farm Weeds of Canada. Ottawa, Ontario, Canada: Agriculture Canada.
Clerck-Floate R de, SchwarzlSnder M, 2002. Host specificity of Mogulones cruciger (Coleoptera: Curculionidae), a biocontrol agent for houndstongue (Cynoglossum officinale), with emphasis on testing of native North American Boraginaceae. Biocontrol Science and Technology, 12(3):293-306; 35 ref.
Cochrane TS, 1975. Notes on the flora of Wisconsin. 1. New and corrected distribution records of Boraginaceae. Michigan Botanist, 14:115-123.
Cockayne TO, 1961. Leechdoms, Wortcunning, and Starcraft of Early England. Vol. 1. London, UK: The Holland Press.
Conner RL, Declerck-Floate RA, Leggett FL, Bissett JD, Kozub GC, 2000. Impact of a disease and a defoliating insect on houndstongue (Cynoglossum officinale) growth: implications for weed biological control. Annals of Applied Biology, 136(3):297-305; 27 ref.
Cranston RS, Pethybridge JL, 1986. Report on houndstongue (Cynoglossum officinale) in British Columbia. British Columbia Ministry of Agriculture and Food, Internal Report, 8 pp.
Cranston RS, Ralph DE, 1983. Evaluation of fall applied herbicides for houndstongue (Cynoglossum) control on rangelands. Expert Committee on Weeds (Western Section), Research Report 3:126-127.
Cranston RS, Ralph DE, Falsetta P, 1983. Evaluation of spring applied herbicides for houndstongue (Cynoglossum) control on rangeland. Expert Committee on Weeds (Western Section), Research Report 3:68-69.
Cranston RS, Wood JA, 1986. Picloram rates for houndstongue control. Expert Committee on Weeds (Western Section), Research Report 3:68-69.
Frankton C, Mulligan GA, 1970. Weeds of Canada. Canadian Department of Agriculture Publication 948. Ottawa, Canada: The Queen's Printer.
Freijsen AHJ, Troelstra SR, Kats MJ van, 1980. The effect of soil nitrate on the germination of Cynoglossum officinale L. (Boraginaceae) and its ecological significance. Oecologia Plantarum, 1:71-79.
Gains XM, Swan DG, 1972. Weeds of the eastern Washington and adjacent areas. Davenport, USA: Camp-Na-Bor-Lee Association, Inc. Publ.
Greatorex JC, 1966. Some unusual cases of plant poisoning in animals. Veterinary Record, 78:725-727.
Knight AP, Kimberling CV, Stermitz FR, Roby MR, 1984. Cynoglossum officinale (hound's-tongue)
Lodge WR, Campbell JB, Smoliak S, Johnston A, 1971. Management of the western range. Publication 1425. Ottawa, Canada: Canadian Department of Agriculture.
Love A, Love D, 1956. Cytotaxonomical conspectus of the Icelandic flora. Acta Hortic. Gotoburgensis, 20:65-290.
Macoun J, 1884. Catalogue of Canadian Plants. Part 1 - Gamopetalae. Canada: Dawson Brothers.
Mandryka II, 1979. Cynoglossum officinale (Hound's tongue) as a poisonous plant. Veterinarya, 9:69-70.
McGaw BA, Wooley JG, 1979. The biosynthesis of angelic-acid in Cynoglossum officinale. Phytochemistry, 18:1647-1649.
Muenscher WC, 1980. Weeds. Cornell University Press, Ithaca, New York and London, 586 pp.
Mulligan GA, 1957. Chromosome numbers of Canadian weeds. Canadian Journal of Botany, 35:779-789.
Powell GW, Sturko A, Wikeem BM, Haris P, 1994. Field Guide to the Biological Management of Weeds in British Columbia. Land Management Handbook No. 27. Canada: British Columbia Ministry of Forests.
Resch JF, Meinwald J, 1982. A revised structure for acetylheliosupine. Phytochemistry, 21:2430-2431.
Schroder D, 1976. Investigations on the natural enemies of some Canadian weeds. Trinidad, Commonwealth Institute of Biological Control: Report of work carried out during 1975. Trinidad, West Indies, Commonwealth Institute of Biological Control, 36-38.
Scoggan HJ, 1978. The flora of Canada, Part 3 - Dicotyledoneae (Saururaceae to Violaceae). Ottawa, Quebec, Canada: National Museum of Natural Sciences, National Museums of Canada, 568 pp.
Skalinska M, Czapik R, Piotrowicz M, 1959. Further studies in chromosome numbers of Polish angiosperms (Dicotyledons). Acta Soc. Bot. Poloniae, 28:487-529.
Svensson R, Wigren M, 1982. Competition and nutrient experiments illustrating the decline of some village weeds. Svensk Botanisk Tidskrift, 76:51-65.
Taylor RL, MacBryde B, 1977. Vascular plants of British Columbia: A descriptive resource inventory. Technical Bulletin No. 4. The Botanical Garden, Vancouver, Canada: University of British Columbia Press, 745 pp.
Upadhyaya MK, Furness NH, 1994. Influence of light intensity and soil moisture stress on leaf surface characteristics of Cynoglossum officinale, Centaurea spp., and Tragopogon spp. Canadian Journal of Botany, 72:1379-1386.
US Fish and Wildlife Service, 2013. In: Endangered and Threatened Wildlife and Plants; Endangered Status for Gunnison Sage-Grouse; Proposed Rule. 78(8) US Fish and Wildlife Service, 2486-2538. https://www.gpo.gov/fdsys/pkg/FR-2013-01-11/pdf/2012-31667.pdf
USDA-ARS, 2003. Germplasm Resources Information Network (GRIN). Online Database. Beltsville, Maryland, USA: National Germplasm Resources Laboratory. https://npgsweb.ars-grin.gov/gringlobal/taxon/taxonomysearch.aspx
USDA-NRCS, 2002. The PLANTS Database, Version 3.5. National Plant Data Center, Baton Rouge, USA. http://plants.usda.gov.
Distribution MapsTop of page
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