Euonymus japonicus
(Japanese spindle tree)

Euonymus japonicus is native in Japan (and perhaps China and Korea) but has been widely introduced for cultivation as an ornamental or hedge plant. It has become naturalized in other Asian countries, a number of states in the USA, and in some European countries including the UK. It is of concern for its potential to be invasive. E. fortunei, which is closely related, is already proving invasive in some regions. In New Zealand, E. japonicus is cited as a ‘weed of concern on conservation lands’ (Invasive Plants Database, 2017). In Australia, it has been ranked as an environmental weed and declared weed (regulated) ‘with the potential to have serious impact' (Randall, 2007). E. japonicus was included in the Life IAP-Risk list of 37 potentially invasive species to the EU (Tanner, 2017), but was subsequently removed due to a lack of adequate information (Life IAP-Risk, 2016). As the seeds are dispersed by birds it has the potential to readily spread outside cultivation.

According to most sources, E. japonicus, is only native to Japan but some sources, e.g. World Agroforestry Centre (2017), indicate that it is also native to China and Korea. E. japonicus has been widely introduced for cultivation as an ornamental or hedge plant. This is well documented in many countries in Europe (DAISIE, 2017; Flora Europaea, 2017; Online Atlas of the British and Irish Flora, 2017), USA (USDA-NRCS, 2017), South and South East Asia (Flora of China Editorial Committee, 2017; USDA-ARS, 2017), Australia (Randall, 2007) and New Zealand (GBIF, 2017), and locally in South America (Bolivia) (Missouri Botanical Garden, 2017), and may well occur in more countries than are indicated in this datasheet. It has naturalized in some parts of the USA (USDA-NRCS, 2017) and Europe (DAISIE, 2017), and elsewhere (GBIF, 2017).

There is a high risk of introduction, due to its popularity as an ornamental plant. The likelihood of it becoming invasive when introduced is far less certain. As the seeds are dispersed by birds it has the potential to readily spread outside cultivation.

In the UK it has naturalized in woodland, on sea-cliffs and roadsides (Online Atlas of the British and Irish Flora, 2017; PFAF, 2017). In China it occurs from sea level up to 1400 m.

Genetics

The chromosome number of E. japonicus is 2n = 32 (Missouri Botanical Garden, 2017).

Reproductive Biology

E. japonicus reproduces by seed. Flowering occurs in early summer and flowers are pollinated by bees and flies. Seed is dormant when shed and requires stratification. Stored seeds require 3 months of cold stratification, and can take up to 18 months to germinate (PFAF, 2017). Increasing the period of cold stratification can improve the rate of seed germination to 65% after 60 days germination. Soaking the seeds in gibberellin can further enhance germination. Optimum germination occurs at about 25^°C (Xue, 2011).

For commercial purposes propagation can be obtained from cuttings (Tawfik, 2001).

Physiology and Phenology

E. japonicus is an evergreen shrub with a periodic growth pattern consisting of several growth flushes per year. In each flush, 9-11 nodes are added to the stem length. Nodes formed at the beginning of a growth flush are short and bear scale-like leaves. In the middle of the flush, the nodes are longer and become shorter again toward the end of the flush (Zieslin and Pines, 1987).

Longevity

Trees may live for up to 150 years (Urban Forest Ecosystems Institute, 2017).

Environmental Requirements

E. japonicus tolerates temperatures as low as -10°C (PFAF, 2017) and is rated by PFAF (2017) as being tolerant to both UK and USA hardiness zones 7 (down to -20°C). It also has a wide tolerance to different soil types and acidity levels and some tolerance of salinity (Urban Forest Ecosystems Institute, 2017). It does not tolerate deep shade but has medium shade tolerance (Lin ShuYan, 2007). Plants are very tolerant of maritime exposure, succeeding even when grown on the seashore but they can be killed by cold drying winds (Useful Tropical Plants, 2017).

When grown as an ornamental, it tolerates light, medium and heavy (clay) soils, but prefers well-drained soil. It also tolerates acid, neutral and basic (alkaline) soils. The plant prefers night temperatures of 4-12°C and day temperatures of 19°C or lower.

A wide range of pests and pathogens have been recorded on E. japonicus, scale insects, thrips and powdery mildew are perhaps the most common causes of damage.

Major host of:

Colletotrichum boninense; Erysiphe euonymi-japonici; Luperomorpha xanthodera; Parthenolecanium persicae (peach scale); Senecio vulgaris.

Minor host of:

Alfalfa mosaic virus (alfalfa yellow spot); Armillaria luteobubalina (armillaria root rot); Ceroplastes floridensis (soft scale); Ceroplastes japonicus (tortoise wax scale); Cydalima perspectalis (box tree moth); Epiphyas postvittana (light brown apple moth); Exomala orientalis (oriental beetle); Metcalfa pruinosa (frosted moth-bug); Pratylenchus penetrans (nematode, northern root lesion).

Wild host of:

Aphis fabae (black bean aphid).

Host of:

Aphis fabae cirsiiacanthoidis; Fusarium oxysporum (basal rot); Pryeria sinica (pellucid, zygaenid (Japan)); Unaspis euonymi (euonymus scale).

Pryeria sinica (Euonymus leaf notcher) is newly recorded in the USA (University of Maryland Extension, 2017). E. japonicus is noted to be susceptible to scales, spider mites and thrips, oak root rot, powdery mildew and root rot (Urban Forest Ecosystems Institute, 2017).

In California, E. japonicus can be heavily infested by the light brown apple moth, Epiphyas postvittana, an exotic introduction from Australia (Wang et al., 2012).

Unaspis euonymi is found in the centre of Brussels, Belgium, and in Belgrade, Serbia, causing severe leaf loss and dieback (Graora, 2007; Malumphy, 2016)

Heavy infestations of Eutetranychus orientalis have been recorded in Shandong, China (Sun et al., 1996).

Rhizoctonia solani [Thanatephorus cucumeris] can be a serious problem in seedling nurseries of E. japonicus (Lee et al., 1996).

Paratylenchus dianthus was found to cause severe leaf drop of E. japonicus in Chongqing, China (Liu, 1995).

It may also be a host of the sugar beet fly, Pegomya mixta [Pegomya cunicularia] (PFAF, 2017).

Environmental

• Agroforestry
• Amenity
• Landscape improvement
• Revegetation
• Soil conservation

General

• Research model

Medicinal, pharmaceutical

• Source of medicine/pharmaceutical

Ornamental

• Propagation material

E. japonicus is very similar to E. fortunei but is more erect, growing to 3 m tall, while the latter has a climbing or procumbent habit (Flora of China Editorial Committee, 2017). It is distinguished from most other species by its leathery leaves and smooth, rounded fruit, not lobed (Stace, 1997; Schulz, 2006).

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.

Physical/Mechanical Control

Established plants can be removed by cutting and by uprooting if small enough, but larger stumps may need to be covered with thick black polyethylene to exclude light (Forest and Bird, 2017).

Biological Control

E. japonicus is damaged by a wide range of insects, pathogens and nematodes but there are no reports of attempts at exploiting these for biological control.

Chemical Control

The growth of E. japonicus can be inhibited by the growth regulator paclobutrazol (Keever et al., 1990); also by uniconazole (Norcini and Knox, 1990); and by dikegulac (Yamazaki et al., 1979) but these would only limit the size of established plants. In New Zealand, recommendations include cutting and painting the stump with a 1-2 mm layer of metsulfuron gel; also spraying foliage with metsulfuron (Forest and Bird, 2017). Glyphosate is not included as a means of control in New Zealand but it is known to be mildly damaging to the foliage and GISD (2017) recommendations for control of the closely related E. fortunei include the application of glyphosate or triclopyr to freshly cut stems.

08/02/17 Original text by:

Chris Parker, Consultant, UK

Pedro Acevedo-Rodríguez, Department of Botany-Smithsonian NMNH, Washington DC, USA