C. japonica is native to eastern Asia (USDA-ARS, 2009) and is recorded as a significant weed of fruit and ornamental trees in Japan, China and neighbouring countries, but has now been repeatedly introduced to USA, apparently deliberately as a medicinal plant. It was first recognised in SE USA in the 1940s and was believed to be eradicated but there have been further occurrences in Texas (since 2001), and, since 2004, in California (USDA-NPAG, 2001; Hrusa and Kelch, 2006; Texas Invasives, 2007). It has proved locally invasive and damaging to fruit and ornamental trees and is the subject of intensive eradication efforts. Eradication has been achieved at many sites but there is continued introduction.
While many botanists have adopted the APG III system of classification for the orders and families of flowering plants which places Cuscuta in the family Convolvulaceae, the CAB Thesaurus continues to use the Cronquist system which places it under Cuscutaceae.
Cuscuta japonica, with a single style falls in section Monogyna of the genus, which also includes the weedy species C. reflexa, C. monogyna and C. lupuliformis (Yuncker, 1932).
Flora of China (2009) lists two varieties var. formosana (Hayata) Yuncker, and var. japonica. It also refers to some possible confusion with C. engelmannii Krock in some localities in China. Otherwise C. japonica appears to be a well-recognised and well-defined species, free of nomenclatural uncertainties.
C. japonica is usually an annual but in California it is observed to over-winter and behave as a perennial (Tidwell, 2008). It is a typical parasitic dodder with yellowish vines 1-2 mm in diameter, almost devoid of chlorophyll, much branched. The vines twine anti-clockwise around the host stems and foliage. Leaves are absent, represented only by small hooded bracts, the same colour as the stems. The inflorescence is a loose spike about 3 cm long, of 5-10 sub-sessile flowers, each supported by 2 mm ovate bracts or bracteoles. Calyx are cup-shaped about 2 mm across, and deeply divided. Sepals are whitish, colourless or occasionally purplish, almost circular, sub-equal, and tuberculate on the lower sides. The corolla is white, campanulate/tubular, 3-7 mm long with 5 shallow lobes erect or deflexed, ovate-triangular, and much shorter than the tube. Stamens are inserted at the throat, anthers yellow on very short or no filament. Scales are oblong, fimbriate, and half as long as the tube. The ovary is spherical and smooth. The single style is about equal to the ovary, with two stigmas, much shorter than the style. The mature capsule is ovoid about 5 mm in diameter. The seeds brown, 2-2.5 mm, 1-3 per capsule. (Based on Flora of China, 2009 and other sources.)
C. japonica var. japonica has tongue-shaped stigma lobes, while in var. formosana they are quadrangular. In Taiwan, var. formosana also has larger flowers 4-7 mm long v. 3-5 mm long in var. japonica (Liao et al., 2000). The pollen morphology of both these varieties is described by Liao et al. (2005). The ultrastructure of the embryo has been described by Lee (2007a). The form observed in USA corresponds to var. japonica.
C. japonica is native to eastern temperate Asia, mainly in Japan, China,Taiwan and South Korea, with distribution extending to more tropical conditions in southern China and Vietnam (Flora of China, 2009; USDA-ARS, 2009). It has been introduced to USA, apparently many times, over the past 30-40 years. USDA-NRCS (2009) still records it as occurring in Florida and South Carolina, though another USDA source suggests that it was eradicated from both Florida and South Carolina (USDA-NPAG, 2001). Both sources confirm continuing occurrence in Texas, while further introductions have now been recorded in California (Hrusa and Kelch, 2006).
Liao and Tsai (1990) refer to C. japonica being newly recorded in Taiwan, but Kuoh and Chiang (1989) had already recorded C. japonica var. formosa occurring on at least 36 host species in Taiwan a year earlier. Hence the status of C. japonica in Taiwan is not completely clear but it is assumed to be native there.
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.
According to USDA-NPAG (2001), C. japonica was introduced to a number of sites in USA, in Texas, Florida and South Carolina from 1940s onward but was apparently eradicated. It was subsequently re-introduced to Texas about 2001 and continues to persist there, while also now occurring quite widely in California, as a result of deliberate introduction as a medicinal herb and by subsequent accidental or (mainly) deliberate spread in the field (Hrusa and Kelch, 2006).
The risks of introduction are apparently high to judge from the large number of sites where it has been detected in California. Some of these (over 200) sites may be the result of local re-distribution, but many are believed to be the result of deliberate importation of living shoots of the plant as a herbal medicinal material.
C. japonica is mainly a plant of warm temperate conditions. In Japan, it is described as a plant of roadsides and waste places (Morita, 1997). In Taiwan it occurs mainly in a zone between 1000 and 2000 m above sea level. In USA it occurs to some extent in fruit orchards but primarily in amenity trees and shrubs in urban situations.
C. japonica has a relatively wide host range which includes herbs, woody plants and ferns. Liao et al. (2000) record 36 host species in Taiwan: Zaroug and Ito (1988) record 32 hosts in 16 different families in Japan. The latter authors also note that while C. japonica grew very well on aubergine and potato, it showed limited vigour on pumpkin (Cucurbita moschata), was relatively weak on soyabean and did not persist on maize, tomato or Trifolium pratense, apparently due to a hypersensitive response. Pea, cucumber and Brassica campestris were immune. Euphorbia pulcherrima is described by Christensen et al. (2003) as ‘partially incompatible’, developing abnormal ‘coral-like’ growth, before apparently normal shoot growth, but the latter die before flowering. Hu et al. (2005) describe somewhat different virulence on a range of hosts including Wedelia chinensis, Broussonetia papyrifera, Ipomoea cairica and Lantana camara. Tree crops affected include several commercial fruit species (apple, citrus, grape) and also ornamental trees which are apparently the main hosts in USA. In Texas, 20 hosts have been recorded (Camilli, 2003).
Growth Stages
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Flowering stage, Fruiting stage, Vegetative growing stage
C. japonica reproduces both by seed and vegetatively. The flowering of Cuscuta species has been linked in different studies either to the flowering of the host, or, in C. reflexa particularly, to short days. In China, flowering occurs in August and fruiting in September, while in California it occurs very late in the season in the north of the state, suggesting that it is reacting to the shorter days of the autumn, but no specific study has been reported. Fortunately whether because of the late flowering or for lack of fertilization, seed set has not so far occurred in California (Tidwell, 2008). It has been confirmed that C. japonica is self-sterile (Tidwell, 2008) and the populations in California may be largely clonal. The presence of extra floral nectarines supports the assumption of insect pollination (Schaffner, 1980). Seed set does apparently occur in Texas and there is comment that a single plant can yield over 2000 seeds (Texas Invasives, 2007) with viability for 20 years (GBEP, 2006).
Vegetative spread occurs via the stems either naturally or deliberately by transfer of lengths of detached stem.
C. japonica can behave as an annual or, at least in California, as a perennial, readily surviving mild winters.
Physiology and Phenology
Cuscuta species are obligate parasites with negligible chlorophyll, totally dependent on attachment to a host plant within a short period after germination. Germination does not depend on the presence of host plants but occurs over a prolonged period as a proportion of hard-coated seeds gradually become permeable and allow absorption of water. This ensures that not too many seeds germinate at one time in the possible absence of a potential host plant. In many species, there is also an innate dormancy which is broken by chilling over the winter. There is a scarcity of information on the germination behaviour of C. japonica, but Lee (2007b) in his studies of the ultra-structure and development of the seedlings, used the standard procedure, for Cuscuta spp., of scarification by concentrated sulphuric acid to obtain germination for his studies, and it is assumed it is similar in its behaviour to other Cuscuta spp. On germination a very short root is formed which provides anchorage only, while the plumule elongates rapidly and, in the light, circumnutates widely anticlockwise until contact is made with a stem or other solid object. The length of the seedling rarely exceeds 10 cm and if a host is not located, the seedling dies. In most species the seedlings are not expected to survive more than a few days, but according to Camilli (2003) seedlings of C. japonica may survive for several weeks in the absence of a host. Once contact with a stem or other object is made, the shoot will twine around it, whether living or inanimate and the root and shoot base below this point will soon die. The anticlockwise coiling action requires blue or far-red light (Furuhashi et al., 1995) and is suppressed under red light or darkness. If a suitable host stem is found, several coils will develop, with pre-haustorial swellings on the inner face of the coiled stem, from which full haustoria develop in the presence of cytokinins, which derive partly from the parasite and partly from the host. Haustorial initiation may also involve calmodulin (Huang and Li, 1991). It also depends on blue or far-red light, with far-red being the much more effective (Furuhashi et al., 1995, 1997; Tada et al., 1996). Intrusive organs develop from the haustorium and searching hyphae penetrate the host tissues by a combination of separation and penetration of cells (these processes reviewed by Parker and Riches, 1993). Connections are then formed by a bridge of tracheids with the host xylem, while connection with the phloem via plasmodesmata between searching hyphae and host parenchyma cells has also been confirmed in C. odorata by Dorr (1987). Development of the tracheids and sieve tubes in C. japonica is described by Huang and Li (1987).Structure and development of the upper haustorium of C. japonica are also described by Lee (2007c). Once the haustorial connection is complete, new shoot buds develop close by, leading to the outgrowth of shoots which can elongate at a rate of 15 cm per day.
Although C. japonica stems normally show little sign of green-ness, there are well-developed chloroplasts: Lee KyuBae (2007d) and van der Kooij et al. (2005) have shown that there is a significant level of photosynthesis, comparable to, or greater than, that of C. reflexa. Chlorophyll content and photosynthetic activity are greatest in starved plants, e.g. in seedlings before attachment to the host, although the green colour is generally masked by the high levels of yellow carotenoids. This photosynthetic capacity clearly contributes to the unusual ability of seedlings (and stem fragments) of this species to survive for several weeks before attaching to a host.
Vegetative growth may continue for some time before any flowers are formed, or flowering may occur very rapidly. Flowering is thought by some authors to be linked to the flowering of the host plant but this is not apparently consistent.
The physiological effects of C. japonica on its hosts are discussed under Impacts.
Guo and Li (2000b) recorded Alternaria tenuis [A. alternata], Fusarium semitectium [Fusarium pallidoroseum] and Pestalotiopsis guepini [Pestalotia guepinii] as fungi occurring on C. japonica. Guo et al. (1998) had previously shown that Fusarium solani from Cuscuta reflexa was also pathogenic on C. japonica in China, though it is not clear whether this species occurs naturally on C. japonica.
While some other Cuscuta species have been found to enter USA in medicinal herb preparations, which are supposed to be crushed and should not contain viable seeds but do so, it appears that most if not all introduction of C. japonica occurs as vegetative material, deliberately introduced by passengers from Asia (Fred Hrusa, California Department of Food and Agriculture, USA, personal communication, 2009).
At the local level there can be a steady spread of established infestations by vegetative growth, or via discarded garden waste, or by birds using it for nesting material, but again there is suspicion that most spread is due to deliberate transfer of Cuscuta stems by those interested in growing and using the material for medicinal purposes.
Natural Dispersal (Non-Biotic)
Cuscuta species have no specialized dispersal mechanism and movement is assumed to occur by wind and water.
Vector Transmission (Biotic)
The main biotic dispersal agent of C. japonica, both locally and internationally, is man, as seeds and vines are transported for use in medicinal herb products.
Accidental Introduction
At the local level there may be accidental movement as a result of soil movement, and disposal of garden waste. At the international level, it has been suggested that some of the introductions to USA may have resulted from contamination of kudzu vine (Pueraria lobata) (Yuncker, 1965; O’Driscoll, 2003).
Intentional Introduction
While some introductions into USA may have arisen from deliberate introduction of herbal products accidentally contaminated with whole viable seeds, most are thought to be the result of deliberate smuggling of vegetative material for medicinal purposes (Fred Hrusa, California Department of Food and Agriculture, USA, personal communication, 2009).
Cuscuta spp. are known to be powerful sinks for metabolites, causing a severe drain on host resources and often completely preventing normal fruit development, as shown by Wolswinkel (1979) for C. europaea on faba bean. This powerful metabolic sink effect was studied and described in detail by Wolswinkel and Ammerlaan (1983). Wang et al. (2007) also record reductions in the photosynthesis of hosts parasitized by C. japonica.
The damage from Cuscuta spp. to infected hosts can be severe, to the extent of total crop loss and a number cause significant economic loss, especially C. campestris, on lucerne and a range of horticultural and agricultural crops. Woods et al. (2008) note that trees infested by C. japonica can be completely smothered and killed but it has not been recorded as a major threat to crops in its native area, and the damage to fruit and ornamental trees in USA is extremely localized and limited as it is routinely subject to eradication. However, economic loss can occur due to the direct cost of eradication programmes and the damage sustained to host plants in the course of eradication measures. Loss could also occur when the possible contamination by the parasite leads to quarantine restrictions on sale or movement of produce.
Cuscuta species can act as bridges for the transmission of viruses and mycoplasma-like organisms, and C. japonica has been shown to transmit the causal agent of witches’ broom from one host to another (Zhang et al., 1991). Such transmissions are usually deliberate for research purposes but it is possible that they could occur accidentally and cause additional impact in that way.
There is considerable potential for a damaging effect of C. japonica on biodiversity if it were allowed to flourish. The parasite has a limited and fairly specific host range which could result in a change in the flora of a habitat due to selective parasitization. However, so far it has not been allowed to realise this potential in the USA.
Most of the concern over this species as an invasive weed arises from its economic value as a herbal medicine and the deliberate introduction and propagation that this has encouraged in USA. Several Cuscuta species are used in Chinese herbal remedies under the term ‘Semen Cuscutae’ (or ‘tu si zi’ in Chinese). Li et al. (2000) state that Semen Cuscutae is originally specified as the dry ripe seed of C. chinensis in China Pharmacopoeia. However, a survey of the herb market showed that C. australis was the main source and C. japonica was also a source in some areas. Their paper further shows that the content of sesamin (a lignan with dietary fat-reduction potential) is highest in C. chinensis and not detectable in C. japonica. Content of sesamin was higher in stems than in seeds, and it appears that stems are frequently used as a source material as well as seeds. According to Du et al. (1998), the preferred species is C. chinensis but C. australis and C. japonica are now often used because of the ‘decline in the production capacity of C. chinensis’. Ye Min et al. (2002) however show that C. australis has a much higher flavonoid content than either C. chinensis or C. japonica and comment that ‘the quality of Semen Cuscutae can be evaluated according to the content of flavonoids’. The properties attributed to these ingredients include ‘replenishing the kidney essence or ‘jing’ in order to support healthy sexual and reproductive functioning’; ‘nourishing the liver and brightening the eyes’; indications include ‘Impotence, seminal emission, dripping of urine after urination, enuresis, frequent urination, aching and weakness of the loins and knees, blurred vision and tinnitus; threatened abortion due to deficiency of the kidney; diarrhea due to hypofunction of the spleen and the kidney; external use for vitiligo’. There is evidence to support claims for some of these effects. Qin et al. (2000) confirm that extracts from seeds of C. chinensis ‘invigorate the reproductive system and reproductive endocrine function in male rats’. Oh Hyuncheol et al. (2002) confirm that derivatives of a caffeoylquinic acid from C. japonica have activity in keeping with reputed antihypertensive action of ‘Cuscuta Semen’. Yang et al. (2006) show that an extract of C. japonica can significantly protect the human sperm from damage caused by reactive oxygen species. Many other studies involve treatment with a combination of Cuscuta extracts with other herbs, making it difficult to judge the value of the Cuscuta itself.
Extracts of C. japonica have shown anti-fungal activity against Alternaria mali (Kim et al., 1993).
Social Benefit
C. japonica is widely valued in Asia for its medicinal benefits, and is likewise valued by some communities of Asian extraction in USA.
Environmental Services
It is doubtful that C. japonica can be said to provide any environmental service.
Identification of C. japonica from seed morphology is difficult. In the field, flowering specimens are not difficult to distinguish from other species, while the hooded leaf-bracts distinguish it from all the native American species. This is now also achieved by the use of RFLP techniques which have been developed to help distinguish C. japonica tissue from native American species in the vegetative stage (Woods et al., 2008). It is not clear whether this latter technique allows discrimination of seed (or crushed seed) samples. C. chinensis and C. australis were not included in the work by Woods et al. but would presumably not be confused as their profiles would be more comparable to other members of the Grammica section of the genus.
Detection of C. japonica in USA has involved visual inspection of imported herbal products and germination studies to check for viable seed. In the field it has been detected by surveys of residential neighbourhoods, concentrating on those known to have Asian immigrant populations. Aerial surveys are being considered (Tidwell, 2008).
C. japonica is distinct from other weedy Cuscuta species in having a single style, longer than the stamens, with two short but distinct stigmas. In C. lupuliformis the single style is shorter and the stigmas are little more than lobes. In C. reflexa and C. monogyna also there is only a single style but it is extremely short or non-existent. The seeds of C. japonica can be distinguished from those of C. monogyna by the exposed hilum, and scar area square and flush with the surface (hilum hidden and scar area narrow-rectangular and hidden in C. monogyna).
As most infestations of C. japonica in California do not flower, a means of successfully distinguishing it from native North American Cuscuta species in the vegetative stage has been developed by Woods et al. (2008), using RFLP (restriction fragment length polymorphism). C. australis and C. chinensis were not included in that study but as they fall in section Grammica of the genus rather than section Monogyna, they are also unlikely to be confused. Hu et al. (1997) had previously shown that preparations from seed of C. japonica, C. chinensis and C. australis could be distinguished on the basis of HPCE (high performance capillary electrophoresis).
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
Prevention
SPS measures
Many countries include all Cuscuta species in their official lists of prohibited, quarantine species. Holm et al. (1997) indicate that 25 countries have declared Cuscuta spp. as noxious, and that the movement of Cuscuta-infested material is prohibited in every state of the USA.
Dry heat at 100°C for 15 minutes has been shown to selectively kill seeds of Cuscuta spp. in nigerseed (Guizotia abyssinica) (Strasser, 1988) providing a means of de-contaminating contaminated imports but this has not had to be applied to the problem of C. japonica.
Eradication
Successful eradication of C. japonica has been reported from some sites in USA. It is recorded that C. japonica was identified on the Clemson University site in South Carolina in 1971 (Invasive Plants of the Eastern United States, 2003). In 1991 it was decided to eradicate the infestation starting with removal of all C. japonica mats, then using herbicides glyphosate and dacthal to kill all host and parasitic vegetation within the infested site, followed by a controlled burn to fully destroy the vegetation and any seeds on the soil surface, fumigation with methyl bromide and sterilization with Vapam and Basamid granules.
Control
Cultural control and sanitary measures
Methods for Cuscuta spp. in general include the use of clean seed.
Physical/mechanical control
Control of an established Cuscuta infestation may start with manual removal of the vegetative mass of the parasite from a woody host plant, or by mowing where it occurs on a herbaceous host. This may be followed by fire, before or after use of a herbicide. If there is evidence of germination from seed, the seedlings my need to be destroyed by repeated tillage.
Movement control
Movement of Cuscuta material must be minimized by cleaning equipment leaving an infested site and by controlling the movement of domestic animals.
Biological control
Melanagromyza cuscutae and the gall-forming weevils Smicronyx spp. have been tested for control of other Cuscuta spp. Similarly the fungi Alternaria cuscutacidae and Colletotrichum gloeosporioides have shown promise in some situations but none have proved reliable enough for use in practice. On C. japonica, a number of fungi have been studied for their potential as biocontrol agents, including Fusarium solani, F. semitectum, Pestalotiopsis guepini [Pestalotia guepinii] and Alternaria tenuis, but they have not yet been fully developed for use (Guo et al., 1998; Guo and Li, 2000).
Chemical control
Literature on C. japonica in USA refers to the use of pre- and post-emergence herbicides but few specific compounds are named. In the case of pre-emergence herbicides, trifluralin is mentioned by GBEP (2006) and others could include pendimethalin which is used successfully in legume crops for control of other Cuscuta spp. including C. campestris; and perhaps imidazolinone herbicides including imazaquin. Post-emergence, glyphosate, glufosinate and dacthal have all been used effectively. Herbicides may also be injected into the trunks of infested trees, to kill both parasite and host to prevent spread when trees are felled and utilized (Texas Invasives, 2007).
Host Resistance
There is no evidence for host varietal resistance to C. japonica.
Monitoring and Surveillance
Detection of C. japonica in USA has involved visual inspection of imported herbal products and germination studies to check for viable seed. In the field it has been detected by surveys of residential neighbourhoods, concentrating on those known to have Asian immigrant populations. Aerial surveys are being considered (Tidwell, 2008).
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GBEP, 2006. Japanese dodder. Cuscuta japonica. The Quiet Invasion: A Guide to Invasive Plants of the Galveston Bay Area The Galveston Bay Estuary Program. Japanese dodder. Cuscuta japonica. The Quiet Invasion: A Guide to Invasive Plants of the Galveston Bay Area The Galveston Bay Estuary Program. unpaginated. http://www.galvbayinvasives.org/Guide/Species/CuscutaJaponica
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O'Driscoll CW, 2003. Preliminary review of the genus Cuscuta in North America prepared for the NAPPO PRA Panel - July / August 2003. Pest risk assessment unit, Canadian Food Inspection Agency. Preliminary review of the genus Cuscuta in North America prepared for the NAPPO PRA Panel - July / August 2003. Pest risk assessment unit, Canadian Food Inspection Agency. unpaginated. http://www.nappo.org/PRA-sheets/CuscutaTable2003.pdf
Stefanovic S; Krueger L; Olmstead RG, 2002. Monophily of the Convolvulaceae and circumscription of their major lineages based on DNA sequences of multiple chloroplast loci. American Journal of Botany, 89:1510-1522.
Wang D; Hu F; Chen YF; Yang J; Kong CH, 2007. Photosynthetic characteristics of Cuscuta japonica and its hosts during parasitization and after detachment. Ying Yong Sheng Tai Xue Bao, 18(8):1715-1721.
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Yang X; Ding CF; Zhang YH; Yan ZZ; Du J, 2006. Protection of extract from Cuscuta japonica on human sperm acrosome and ultrastructure. Zhongguo Zhong Yao Za Zhi, 31(5):422-425.
