Clematis vitalba (old man's beard)

C. vitalba produces many seeds that are wind dispersed, and it is a strong colonizer of disturbed ground. It is a fast-growing vine with the ability to climb up and bring down tall trees and reduce standing forests to impenetrable low-growing infestations of the vine. It has the ability to expand its range and cover in Europe, North America, Australia and New Zealand, and to be further introduced as an ornamental species. It is a very serious environmental weed in New Zealand undergoing eradication.

The name 'vitalba' is derived from the Latin words for 'white vine', referring to the mass of white flowers that cover vines in summer. The common name, 'traveller's joy', also refers to this massive floral display, whereas the common names 'old man's beard' and 'virgin's bower' refer to the creamy mass of feathery achenes that hang on the bare canes through winter. Other common names are used regionally in England (West, 1991). Common names in other languages evoke the forest and hedgerow habitat that this vine inhabits. The name 'herbe au gueux' ('beggars plant') is said to originate from the use of the acrid juice of the plant to produce ulcerous wounds as a means of exciting pity (West, 1991). There are no taxonomic synonyms for this species. Several varieties have been recorded, but these are probably phenotypic variations in response to habitat.

C. vitalba is a deciduous, woody climber that can live for 40 years (West, 1991) or more. Woody stems can grow to over 10 m in length and can reach 15-20 cm in diameter. New stems are deeply ridged, dark purple and green, with silky white hairs near the apex, and have been recorded to grow as much as 3 m per year (West, 1991). Stems grow erect between holds, rather than entwining a vertical stem. A shoot can support itself for some distance before twining 3-4 times around a new hold of approximately 1 cm in diameter (Kennedy, 1984; West, 1991). Vines can climb 25 m-tall forest trees, but have difficulty colonizing tall, emergent species with long distances between branches (Ogle et al., 2000). Mature stems have grey, stringy bark, with thickened nodes approximately 15 cm apart. Where stems grow along the ground, adventitious roots form at the nodes. Leaves are opposite, and almost all comprise five 3-10 cm leaflets with long petioles. Leaflets are variable in size and shape, ovate, acute to acuminate, rounded or sub-cordate at the base, and coarsely toothed or entire (Cronk and Fuller, 1995). Leaves have light- and shade-forms (Kennedy, 1984). The flowers are solitary, in terminal or axillary cymes. Flowers are small (c. 2 cm), white to greenish-white, usually hermaphrodite, and without petals (Clapham et al., 1987). The achenes are compressed, 2.0-2.5 mm long. Each retains a feathery style that is 2-3 cm long. Achenes are produced in large heads.

C. vitalba is native to Europe, from southern England and the Netherlands to North Africa, and from Spain to the Middle East and the Caucasus. It is naturalized in European countries bordering its contiguous native range, including Ireland, Poland, Norway and Sweden (Tutin et al., 1964) and it also grows north of its native European range, for example in northern England and Scotland. It has been introduced to, and has naturalized in, North America, Australia and New Zealand. The best means for estimating distribution in Europe appears to be mean temperature in July (Fitter, 1978).

C. vitalba has been introduced widely throughout the world as a garden ornamental, and has naturalized in Europe, North America, and Australasia. Gardeners in Philadephia and Boston, USA imported several Clematis species including C. vitalba between 1830 and 1840 (ACS, 2003). It was first recorded in New Zealand in the 1920s and had become naturalized by 1935 (West, 1991), but it was not until the 1960s that this plant was recognized as a threat.

C. vitalba seeds could be imported between continents as contaminants on trade items. However, this plant is not commonly associated with agricultural or industrial goods. Such events are therefore likely to be rare, and the risk low. However, C. vitalba often grows on roadsides, and the risk of seeds being transported on road vehicles from known infestations to new sites within continents is high. In the past, ornamental Clematis species were often grafted onto C. vitalba rootstocks. It is likely that some incursions of C. vitalba have resulted from reversion of these rootstocks. The highest risk of introduction remains via intentional introduction of the plant as an ornamental, and plants and seed continue to be sold by nurseries, mail order catalogues and websites.

Natural Dispersal (Non-Biotic)The feathery styles assist wind dispersal of achenes (West, 1991) but propagules can also be spread along watercourses.Vector Transmission (Biotic)Dumping of garden waste containing C. vitalba vines onto roadsides has been a significant cause of spread in New Zealand (West, 1992). Achenes can be spread by adhesion to animals. Accidental IntroductionThis weed appears to invade along roadsides by seed, possibly aided by the turbulence created by motor vehicles.Intentional IntroductionC. vitalba is an attractive climber, and was originally introduced to New Zealand, Australia and the USA as an ornamental.

C. vitalba is a minor weed of vineyards, and damages small trees and hedgerows in its native and introduced ranges in Europe (Britt, 1994; Clay and Dixon, 2000) as well as being a weed of pine (Pinus spp.) plantations (Mitchell, 1975).

Keys successfully distinguish C. vitalba from sympatric Clematis species in Europe by flower colour and structure, and by climbing habit. C. vitalba achenes are barely compressed whereas achenes of C. flammula are strongly compressed (Tutin et al., 1964). C. vitalba can be distinguished from C. tangutica because it has white rather than deeply yellow flowers, and because leaves are coarsely rather than finely toothed (Atkinson, 1984).

C. vitalba is a versatile plant capable of growing in a variety of habitats, on a variety of substrates from trees and shrubs in forest margins to hedgerows, fencelines, dunes, riverbanks, and grassland. It is commonly associated with degraded and disturbed areas (Beekman, 1980), and so can be invasive within its native range. In both its native and exotic range, C. vitalba typically occupies forest margins and gaps and can invade open spaces. The distribution of C. vitalba in England is mainly on chalk and limestone, but elsewhere in Europe it occurs on a wide range of moderately fertile, well-drained soils. In New Zealand it is often associated with riverbeds, and fertile alluvial soils (Atkinson, 1984; West, 1991). It does not appear to be unusually sensitive to soil acidity or nutrient deficiency although heavy soils may restrict growth and spread (Atkinson, 1984). Its native range is in the latitudinal range 36-52°N, and it does not thrive north of 36°S. It is a lowland species in New Zealand, suggesting that it is limited by cooler temperatures at high elevation (Atkinson, 1984). In North America it occurs near the coast or on the Great Lakes at latitudes similar to those in Europe (Anon., 2003). These distributions suggest that C. vitalba is a warm temperate species although infestations can occur in microhabitats within regions that otherwise appear inhospitable (Atkinson, 1984). C. vitalba also invades riparian vegetation, waste land, long grass, and even urban areas (Atkinson, 1984; Buxton, 1985; West, 1991). C. vitalba seedlings are readily grazed, and as such C. vitalba is often confined to ungrazed areas (West, 1992).

GeneticsSeveral studies confirm that the species is diploid, with 2n=16 chromosomes (Pastor et al., 1984; Ozyurt et al., 1997). C. vitalba has been artificially hybridized with other species to produce vigorous garden varieties such as C. 'jouiniana' (C. vitalba x C. davidiana or C. vitalba x C. heracleifolia) and C. 'Paul Farges' ('summer snow') (C. vitalba x C. potanini).Physiology and PhenologyBare stems produce leaves in mid-spring, and stem growth is rapid until flowering begins in mid-summer. Inflorescences continue to form as the stem elongates over summer. Achenes form from late summer, are retained on the plant, and fall in late winter or early spring. In New Zealand, there is phenological variation between sites that appears to be related more to microclimatic conditions than latitude or elevation (West, 1992). Seeds require winter-chilling to maximise germination. Hydrated seeds do not survive long, and the dense feathery seed loads hanging in plants over winter can be regarded as a dry, aerial seed bank from which seeds can fall at any time of year. Optimal germination of C. vitalba requires after-ripening of the seeds at temperatures lower than 15°C, and preferably alternating temperatures (Lhotska, 1974; West, 1992). Optimum temperatures and germination success of C. vitalba seeds varied with the duration of winter after-ripening, and this synchronised germination to the optimum period in spring. Similarly, Czekalski (1987) found that germination of seeds collected from plants in the autumn was poor (0-21%) compared to germination of seeds collected from the same plants in the following spring.Seedlings form basal rosettes of single or trifoliate leaves, and after several months produce one or more elongating shoots bearing quinquefoliate leaves. Mature leaders grow 2.0-2.5 m per annum on average (West, 1992). C. vitalba can attain densities of over 7000 stems/ha and a fresh weight increment of 6.3 kg/m²/year. Stems at one New Zealand site grew an average 2.3 m in 1 year, producing 20 new nodes, with secondary stems developing from some of these nodes (West, 1992). Stem diameter and stem rings may not be good indicators of age (West, 1991).Reproductive BiologySeedlings do not flower before the third year (Kennedy, 1984). Flowers are slightly protandrous. Insects visit C. vitalba flowers, but flowers do not appear to be self-incompatible (West, 1992), and pollination can be successful without the attention of insects. West (1992) recorded an average production of 780 viable seeds/m² per year at one New Zealand site, and found 160-900 seeds/m² in the soil. It was estimated that seed might last as long as 5 years in the soil, but no longer than 10 years. Environmental RequirementsC. vitalba grows on well-drained, moderately fertile soils (pH 5.5-8.0) and it is unlikely that poorly drained soils or arid areas will support this species. It responds well to the application of lime but is not restricted to calcareous sites. Plants respond to the addition of calcium and phosphorus (Hume et al., 1995) and to nitrogen (Bungard et al., 1998). The growth and spread of C. vitalba may be restricted by extremely acid soil conditions and by very low concentrations of nitrogen, phosphorus, calcium, sulphur and possibly manganese in the soil. However, it does not appear to be unusually sensitive to soil acidity or nutrient deficiencies (Groppe 1991; Hume et al., 1995). It is somewhat tolerant of saline soils.Seedlings planted within undisturbed forest in New Zealand do not persist, and low irradiance appears to be the primary factor limiting establishment. Under controlled conditions, seedlings achieve maximum growth in full sunlight (100% Ir), substantial growth as low as 10% Ir, and little growth at 3% Ir. Seedlings raised at 1% Ir do not survive (Baars and Kelly, 1996; Bungard et al., 1998). Bungard et al. (1998) studied one forest remnant and suggested that germination and growth in response to light and nitrogen could account for the observed pattern of establishment and success of C. vitalba in New Zealand.It is generally found in Europe only where annual rainfall is greater than 800 mm, and in New Zealand where rainfall is 800-1600 mm (Atkinson, 1984). Otherwise, little has been published on the climatic limits of C. vitalba.

In 1989-90, a field survey identified 81 phytophagous species that attacked C. vitalba in central Europe, including 31 insects, four mites and four nematode species that were regarded as monophagous or oligophagous (Groppe, 1991; Wittenberg and Groppe, 1991, 1992; Wittenberg and Schroeder, 1993; Wittenberg, 1994). A field survey for plant pathogens was carried out in Europe and North America in 1990. Pathogenic fungi were isolated from 57 collections from nine countries (Spiers, 1991; Gourlay et al., 2000).

C. vitalba is generally regarded as a minor weed in European vineyards. However, Angelini et al. (2003) identified a phytoplasma in C. vitalba that is associated with a serious grape disease and it is also a host for Alfalfa mosaic virus (Polak, 1986). They highlighted the risk of disease transmission posed by wild plants such as C. vitalba growing in or near vineyards. C. vitalba is largely an environmental weed in New Zealand, and causes little direct economic damage. However, the total cost expended by the New Zealand Department of Conservation to manage the impact of C. vitalba in native habitats from 1989 to 1994 was approximately US$500,000 (Gourlay et al., 2000; Hill et al., 2001), and total expenditure by all agencies over this period exceeded US$2 million (Hill et al., 2001). C. vitalba is also poisonous to grazing animals but the direct costs of this to the livestock industry has not been quantified (West, 1991).

C. vitalba is not a significant environmental weed in Europe, North America, or Australia. Only in New Zealand has it caused serious environmental damage. C. vitalba infestation can reduce the forest structure, and change the recruitment patterns in forests (Ogle et al., 2000). It grows so strongly in forest margins and light gaps that vines can form a dense, light-absorbing canopy that suppresses all vegetation beneath it and can be so vigorous that the weight of foliage and stems breaks the supporting trees. C. vitalba can reduce small, healthy forest remnants to low, long-lived thickets of vines scrambling over the ground on forest debris (Hill et al., 2001).

Contact with C. vitalba foliage can cause irritant dermatitis in humans. Moore (1971) found the stems and leaves of C. vitalba in the rumen of an 18-month-old cow that died with symptoms consistent with poisoning. However, the toxicity of C. vitalba appears to vary seasonally and it can be controlled by judicious grazing (West, 1991). C. vitalba grows as a dense vertical curtain in forest margins or along the ground as a deep mass of wiry stems restricting access to affected areas by animals and humans. C. vitalba is clearly perceived as a serious social threat by the New Zealand public. Greer and Sheppard (1990) used a contingent valuation method to assess the value that New Zealanders placed on obtaining a solution to this problem. The public was prepared to pay US$22-56 million for research that provided a 'relatively small' likelihood of controlling the weed biologically.

C. vitalba shoots are harvested and eaten in Italy (Pieroni, 1999) and other parts of Europe. Shoots must be boiled to inactivate the toxin protoanemonine (Pieroni, 1999). C. vitalba is also used as a ritual botanical to ward off evil spirits and 'turn away the evil eye' in Tuscany (Pieroni and Giusti, 2002). Leaf decoctions are used in homeopathic medicines for the treatment of urinary tract problems, and to treat inattention and shock. Flower essences are used in treatment of day-dreaming and inattention. There appear to be no recent references to the use of C. vitalba as a rootstock, but this appears to have been common practice in the past. The vigorous and sprawling habit of C. vitalba has been used to stabilize loose, stony slopes (Fisun, 1966). C. vitalba wood has wide vessels and Colville et al. (1979) suggested that carbonized wood of C. vitalba could be used as a matrix for bone regeneration in the treatment of fractures. It is principally used as an ornamental species.