Cynanchum rossicum is a perennial, herbaceous vine. Plants have horizontal, woody rootstalks that form short rhizomes, with abundant pale, fleshy, lateral fibrous roots. Stems are more or less erect, but as plants mature they twine around grasses, each other, or trees for support. Stems are also pubescent in longitudinal bands, and typically reach 60-200 cm, though especially in shaded forest understories plants can grow two to three times this length. Leaves are generally 7–12 cm long and 5–7 cm wide, ovate to elliptical, acute at the tip, and have smooth margins with occasional pubescence. They are arranged oppositely, with the largest leaves occurring in the middle of the stem. Flowers are five-petaled, star-shaped, about 5–7 mm in diameter, and are borne in clusters. The corolla is light pink, reddish brown, or maroon. The fleshy corona is distinctly 5-lobed with the lobes united only at the base, and is slightly darker than the corolla. Fruits are slender, tapered follicles, about 4-7 cm long, and usually form two per flower. The seeds are light to dark brown, obovoid to oblong, may measure 4–6.5 × 2.4–3.1 mm, and have a membranous marginal wing with an apical tuft of hairs (DiTommaso et al., 2005; PCA, 2006). The species twining habit and opposite, glabrous, shiny leaves distinguish C. rossicum from other native and introduced species in the north-eastern US and adjacent regions of Canada (Lawlor, 2009).

Cynanchum rossicum is popularly referred to by its synonym, Vincetoxicum rossicum in literature. Cynanchum rossicum is the currently accepted taxonomy for this species by the Integrated Taxonomic Information System (ITIS, 2010). This species is assigned to the genus Cynanchum by the USDA, the New York State Museum and some other taxonomists in the United States. Gleason and Cronquist (1991), Canadian and European workers assign this species to the genus Vincetoxicum (Lawlor, 2009).\r\n

C. rossicum’s invasion of North America appears to include a very long lag phase (about 100 years) after initial naturalization, followed by an exponentially rapid phase of spread. Researchers believe that the species displays an Allee effect - a reproductive feedback in small plant populations in which population density and reproductive and survival rates are strongly positively correlated (Kricsfalusy & Miller, 2009; Cappuccino, 2004).

Flowering of Cynanchum rossicum can begin as early as mid to late May for populations in central New York and will peak several weeks later in early to mid June. Fruit development typically begins in early June in central New York, with maturity occurring 4–5 weeks after flowering, and finally dehiscence peaking at the end of July (Douglass et al., 2009). Mature C. rossicum ramets typically attain a height of 0.5 /2.0 m before dying back to root crowns in the fall (Cappuccino, 2004).

Cynanchum rossicum is an ornamental vine, and was intentionally introduced into North America, most likely for its horticultural and botanical value. Indeed, for much of the twentieth century plants were available for purchase in the nursery industry (Averill et al., 2008b; Douglass et al., 2009).

Cynanchum rossicum occurs in temperate climates in North America and Eurasia. It has been reported on the edges of alluvial woods, railroad embankments, fencerows, and maple, beech, oak and ash forests in Ontario and western Quebec, and gardens, grassy slopes, and streambanks in southern Ontario. Other recorded habitats include grasslands, such as verges, lawns, old fields, etc., pastures, hedgerows, and gardens. In New York State, it occurs in a variety of habitats , including: calcareous shoreline outcroppings, cliffs, talus slopes, barrens and woodlands; successional old fields, shrublands and forest openings; riverside sand and gravel bars; mesic maple-basswood forests; pasturelands and crop fields; conifer plantations; limestone quarries and dredge spoils; as well as disturbed sites. C. rossicum establishes in full sun or under forest canopies, and while plants may form monospecific stands in all light conditions, growth and fecundity are normally higher in open fields or forest gaps. Plants will tolerate a wide variety of substrates, including silty and sandy loams, glacial till, deep loams, or rocky/gravelly soils, but prefer shallow, calcareous soils. In its introduced range, the distribution of C. rossicum normally includes temperature ranges in the winter of -11 to 0.7°C and in the summer of 20.7–26.4°C, with mean annual precipitation levels of 776–1,206 mm. A mean soil pH of 6.7 at a shaded site and 7.0 at an open site has been observed for C. rossicum (DiTommaso et al., 2005). Research has indicated that generally emergence and establishment of C. rossicum is higher at the upper extent of this range of pH levels (Magidow et al, 2007).

Plants reproduce primarily by polyembryonic, self pollinated, wind-dispersed seeds, but can also expand vegetatively from buds on the root crown (Averill et al., 2008; PCA, 2006; Weston et al., 2005). Individual stems produce large numbers of seeds, with an annual an average of 250 seeds. Seedling survivorship is high, varying from 71 to 100% and, because swallow-wort is self-compatible, a single propagule can initiate a new population. Seeds of this species can also be polyembryonic, a condition in which multiple embryos can arise within a single seed, resulting in the production of multiple seedlings from a single seed (Averill et al., 2008; Averill et al., 2008b). Estimates suggest that 45–75% of seeds produced by C. rossicum are polyembrionic (Douglass et al., 2009). \r\n\r\n

There appears to be a physiological dormancy requirement for C. rossicum seeds, as under experimental conditions, high degrees of germination (greater than 90%) are only found in seeds that are subjected to a stratification treatment of three months (Douglass et al, 2009). Tufted seeds are released from follicles and disperse in late summer and fall (Cappuccino, 2004). Observations indicate that a large proportion of seeds remains close to the parent plant, though small, satellite populations are often found downwind of large seed source populations (Lawlor, 2009). A typical C. rossicum stand can produce as many as 54,000 seedlings per m² annually (Smith et al., 2006). Root crown fragments support dormant buds that readily sprout if not destroyed (PCA, 2006).

Cynanchum rossicum was intentionally introduced to New York state and Canada from Ukraine as an ornamental specimen (Averill et al., 2008b).

Cynanchum rossicum is rapidly invading suitable regions of North America, where it establishes dense monocultures that smother and displace native vegetation (Averill et al., 2008). In a century since its introduction to North America in the late 1800s, C. rossicum has already invaded an area roughly three times larger than it native range in Eurasia, and continues to spread rapidly. \r\n

C. rossicum possesses various allelopathic abilities. For example, plant roots and fruits contain at least two compounds (including (-)-antofine) that have pronounced anti-fungal and anti-feedant activity (Mogg et al., 2008). Leaves release leachates as they decay that negatively affect germination and growth of indicator species (Douglass et al., in press). These root exudates and tissue leachates may play an important role in altering soil microbial and mycorrhizal communities, changes that appear to facilitate C. rossicum’s invasive ability (DiTommaso et al., 2005; Douglass et al., 2009; Smith et alIn New York state alone, C. rossicum displaces and threatens 23 rare plant species and six rare animal species. It has caused significant reductions in arthropod diversity, especially in old field communities, and thus indirectly affects wildlife that prey on insect communities (Averill et al, 2008b; Ernst & Cappuccino, 2005). C. rossicum serves as a population sink for monarch butterflies by attracting oviposition despite being an unsuitable host for larval development. It also displaces common milkweed (Asclepias syriaca), the primary native host for monarch butterflies (Danaus plexippus) (Averill et al., 2008b; Mattila & Gard, 2003; DiTommaso & Antonio, 2003). Dense stands of C. rossicum deter grassland birds from typical nesting habitats in the summer, and can inhibit predation by raptors of small rodents who can take refuge under the abundant and dense senesced plant material during the winter (Averill et al., 2008b; DiTommaso et al., 2005). \r\n

C. rossicum threatens globally-rare alvar communities in the Great Lakes region - which are composed of a unique mixture of sparsely vegetated rock, grassland, and savanna barrens that develop on thin soils over glaciated limestone or dolostone bedrock. Research indicates that C. rossicum populations modify soil microbial communities, thereby displacing sensitive native plant species whose survival depends on unique microbial associations (Averill et al., 2008b; PCA, 2006; Smith et al., 2008). \r\n

C. rossicum has negative effects in agricultural and horticultural ecosystems as well. Christmas tree growers in central New York state have reported increased problems stemming from invasions of the species in plantations, especially within the last decade. Orchard owners east of Rochester, NY cited C. rossicum as their most problematic weed species, since it rapidly and severely alters abiotic and biotic features of tree understories by: decreasing sunlight penetration; increasing nutrient and water acquisition (swallow-wort species have abnormally high root to shoot biomass ratios); and altering rhizosphere dynamics both through shifts in the mycorrhizal communities and the exudation of allelopathic chemicals. Horticultural nursery owners and Christmas tree producers affected by pale swallow-wort infestations have reported that due to a lack of effective control methods, land abandonment was often the most reasonable option (Douglass et al., 2009). Furthermore, C. rossicum has become problematic in no-till corn and soybean fields in several central and western New York State counties. Finally it serves as a host for various insect pests of crops and as an alternate host of Cronartium rusts that attack Pinus species (DiTommaso et al., 2005).

Management of Cynanchum rossicum has proven difficult. Triclopyr and glyphosate have demonstrated effective control when applied as post-emergence foliar spray and cut-stem applications. Both methods require annual follow-up applications, and adequate control will likely be achieved only with 2-3 years of treatments (Averill et al., 2008b; Lawlor & Raynal, 2002, Weston et al., 2005; DiTommaso et al., 2010). Mowing can contain invasive populations of pale swallow-wort, particularly when timed to suppress seed production, but again treatments must be repeated both within a growing season and likely for several subsequent years (Douglass et al., 2009; McKague & Cappuccino, 2005). Additionally, there is some evidence that C. rossicum leaves may leach allelopathic compounds as they decay that can inhibit the germination and growth of species in the soil seedbank (Douglass et al., in press). \r\n\r\n

The noctuid moth Hypena opulenta was discovered feeding on C. rossicum in Ukraine and is being investigated as a potential biological control agent. H. opulenta adults and larvae feed on C. rossicum, and studies have found that releases decreased reproductive output (specifically flower, seedpod, and seed production) in C. rossicum (Weed & Casagrande, 2010). \r\n

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