Clematis terniflora
(sweet autumn clematis)

Clematis terniflora is a perennial woody vine, native to Asia and introduced to North America as an ornamental. It can self-seed, and has escaped cultivation and naturalized in many parts of the USA. It is reported to be invasive in a number of eastern states. It grows in forest margins, scrub, grassy areas on hills and slopes, and in disturbed areas such as roadsides, thickets and urban green spaces. Seeds are widely dispersed by wind. It grows rapidly, forming dense clumps that outcompete and cover young native trees, shrubs and herbs at ground level and suppress seed germination. It can also climb to nearly 10 m, smothering trees and pulling down telephone poles. C. terniflora is difficult to control. Removal by hand can help encourage the growth of native species, but is unlikely to eliminate C. terniflora entirely due to root re-sprouting and prolific seed production. Some herbicides have proven effective in controlling the spread of this species; however, repeated applications are necessary.

C. terniflora is native to China, Japan, Korea, Mongolia, Taiwan and parts of Russia (Flora of China Editorial Committee, 2018; USDA-ARS, 2018). It has escaped cultivation and is naturalized in many parts of the USA, particularly in the East and Midwest (Missouri Botanical Garden, 2018). It is reported as invasive in Alabama, Delaware, Florida, Georgia, South Carolina and Tennessee in the USA (Alabama Invasive Species Council, 2007; SC-EPPC, 2011; FLEPPC, 2017; GA-EPPC, 2018; TE-EPPC, 2018; Delaware Invasive Species Council, 2019). It is also introduced in Canada, Indonesia and Nepal (Roskov et al., 2018).

C. terniflora is still widely available as an ornamental, so it is likely that it will continue to spread into wild areas from gardens, where it is grown.

In the USA, C. terniflora is found along roadsides and in thickets, forest edges, rights of ways and urban green space, especially near creeks (Swearingen and Bargeron, 2016; Flora of North America Editorial Committee, 2018).

In China, C. terniflora is found in forest margins, scrub on slopes, grassy areas on hills, among rocks in coastal areas at sea level to 800 m (Flora of China Editorial Committee, 2018).

Genetics

C. terniflora is tetraploid (2n = 4x = 32) (Wang et al., 2017).

Reproductive Biology

When C. terniflora was grown under natural photoperiods of at least 14 h, flowering was favoured by day/night temperatures of 24/19˚C and 30/25˚C (Suzuki and Hori, 1991). At temperatures of 17/12˚C, shoot growth was delayed and flower buds did not develop (Suzuki and Hori, 1991). Flower buds did not develop under short photoperiods of 8 h or 12 h (Suzuki and Hori, 1991). Spraying plants with GA3 decreased flower numbers and resulted in over 50% of the flowers having degenerated anthers and undeveloped pistils (Suzuki and Hori, 1991).  

C. terniflora is a perennial plant that reproduces both vegetatively and by seed (Global Invasive Species Database, 2010). Seeds (achenes) are small and brown and germinate within 1-9 months (Global Invasive Species Database, 2010). C. terniflora is self-pollinating and a high proportion of its seed is viable (Skibo, 2006).

Physiology and Phenology

With support, C. terniflora can grow to over 9 m high (Global Invasive Species Database, 2010). Where it is unable to climb, it will sprawl across the ground forming dense, 15-30 cm tall and 3 m wide, clumps (Global Invasive Species Database, 2010; Missouri Botanical Garden, 2018).

Flowering occurs from July to September (Flora of North America Editorial Committee, 2018), and flowers attract bees and flies (Burnham, 2013).

Environmental Requirements

C. terniflora prefers full sun or partial shade, where its leaves can be in the sun and its roots in the shade (Floridata, 2015; Missouri Botanical Garden, 2018). It can grow in light (sandy), medium (loamy), or heavy (clay) soils that are fairly well drained. It also tolerates a variety of pH, including highly alkaline settings (Global Invasive Species Database, 2010).

In the USA, C. terniflora grows to elevations of 1000 m, and in China, it has been recorded up to 800 m above sea level (Flora of China Editorial Committee, 2018; Flora of North America Editorial Committee, 2018).

General

• Botanical garden/zoo

Medicinal, pharmaceutical

• Traditional/folklore

Ornamental

• garden plant

The species C. virginiana, native to the USA, is very similar to C. terniflora, although it tends to have toothed leaf margins and is not as prone to self-seeding and spreading as C. terniflora (Swearingen and Bargeron, 2016). The floristic changes in the New York metropolitan region were monitored between two time periods (1901-1950 and 1951-2000) (Clemants and Moore, 2005). It was found that C. terniflora was spreading in the area, whilst the native C. virginiana was declining (Clemants and Moore, 2005).

C. terniflora is easily distinguished from C. occidentalis during flowering as the latter has purple, solitary flowers (Burnham, 2013). 

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

It has been suggested that one way to limit the spread of C. terniflora, is to encourage people to plant alternative species, such as native vines, in their gardens instead (Skibo, 2006).

Control

Physical/Mechanical Control

In a study conducted over six growing seasons, removal of non-native plants, including C. terniflora, either by hand, using chemicals, or a combination of both, led to an increase in native plant cover and richness, and a decline in the abundance of non-native species (Farmer et al., 2016). However, C. terniflora was still a significant community component even after removal treatments, suggesting that it is difficult to control (Farmer et al., 2016).

C. terniflora seedlings can be pulled by hand or mowed, and mature plants can be cut down by hand or mowed (Skibo, 2006). Plants are dormant in winter, making it easier to cut down larger plants at this time (Skibo, 2006).

Chemical Control

In Alachua County, Florida, C. terniflora is treated with foliar applications of the herbicides, glyphosate and pelargonic acid (Global Invasive Species Database, 2010). Glyphosate-based products or growth regulator herbicides such as 2,4-D and Dicamba may be used to control C. terniflora (Skibo, 2006).

In herbicide trials in Florida, imazapic 0.6 g ae/L, glyphosate as low as 3.6 g ae/L, triclopyr as low as 3.6 g ae/L, metsulfuron 0.07 g ai/L, and fluroxypyr as low as 1.8 g ae/L, resulted in 72-99% control of C. terniflora 90 days after application (Langeland and Meisenburg, 2009). It is suggested that repeat applications will be required to control this plant where it is invasive (Langeland and Meisenburg, 2009).

There is a lack of information about the direct effects of C. terniflora on native species, such as C. virginiana. More information is also needed about the costs and timescales required to clear C. terniflora infestations and the potential for use of biological control agents. 

03/06/18 Original text by:

Vicki Cottrell, Consultant, UK