Cynoglossum officinale (hound's tongue)

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.

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).

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.

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).

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).

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).

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).Accidental IntroductionC. 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).

C. officinale is mainly a weed of grasslands, also forests, but can also be a problem in cultivated crops,

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.

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).

GeneticsThe 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 PhenologyC. 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.Reproductive BiologyC. 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.Environmental RequirementsIn 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). AssociationsIn 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).

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.

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.

C. officinale has been reported to cause dermatitis when handled (Muenscher, 1939; Taylor and MacBryde, 1977).

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).