Hedychium coccineum
(scarlet ginger lily)

Hedychium coccineum is an adaptable, tall, herbaceous, and very variable ornamental plant native to Asia. It can colonise natural or semi-natural habitats, from riverine fringe and mountain grasslands to forest understorey. In its introduced range, it can become dominant or co-dominant in natural or semi-natural environments, competing with and displacing indigenous species (e.g. in La Réunion, Africa; Brazil; South Africa). Similarly to other Hedychium species (i.e., Hedychium gardnerianum and H. coronarium), it is widely traded as a garden ornamental around the world. H. coccineum is included in the Global Invasive Species Database (2014) and the Global Compendium of Weeds (Randall, 2012) and is a declared weed and invasive species in some countries. Its environmental adaptability, high commercial appeal and growing impact in countries where it has established suggest its prospective spread in delicate ecosystems cannot be underestimated.

H. coccineum is native to the Indian and Nepalese Himalayas (Bhutan, NE India, Myanmar, Sikkim) China (Guangxi, SE Xizang Province, Tibet, Yunnan Province), and south to Bangladesh Myanmar and northern Vietnam and Thailand. It has a long history of cultivation across southern and south-central Asia. It is naturalized in many regions worldwide including Africa, Sri Lanka, Brazil and the West Indies (Fournet 2002; Govaerts, 2016).

The risk of introduction of H. coccineum is high. This species is well established in commerce, and it is widely sold and traded internationally. H. coccineum and its variant forms/hybrids hold great horticultural value, particularly in the US (including Hawaii), Canada, Australia, UK and across Asia. Currently, H. coccineum is listed as a quarantine pest in Western Australia (Biosecurity and Agriculture Management Act, 2007), and as a Category 1 CARA declared weed in South Africa (Conservation of Agricultural Resources Act, Act 43 of 1983, amended in 2001). This means these plants may no longer be planted or propagated, and all trade in their seeds, cuttings or other propagative material is prohibited. They may not be transported or be allowed to disperse.

In its native range of Asia, H. coccineum is a lower mountain plant which grows on temperate, subtropical forest edges and favours semi shaded sites. H. coccineum in Manipur (northeast district of India) grows between 750 - 1300m and has the widest distributional area of all Hedychium species there, encompassing both the hills and the plains (Sarangthem, 2013). In Sikkim (northeastern Himalayas, India), H. coccineum var. squarrosum grows at higher elevations (2400 - 2700m) (Kumar, 2001). H. coccineum is also known from grassland of mountain areas in Yunnan, China and can tolerate strong sunshine. In its invasive range it is found in moist, shaded sites (e.g. KwaZulu-Natal, South Africa) with reported infestations in natural forest invaded by pines and acacias, below cliffs, north facing areas, moist areas, understorey areas and plantations.

In many sub-tropical countries it has escaped cultivation and naturalised, invading natural and semi natural habitats and forest edges. H. coccineum grows well in the central plateau in Mauritius, where the climate is cool and humid. It tends to be invasive in sub-forest and even abandoned land or gardens. It also grows on riverine fringes, like it does in South Africa.

On the Island of Réunion, Africa, H. coccineum has the potential to invade sparsely planted forests on well drained soils, cliffs and volcanic mountains in the Island interior (Invasive Species Group of Reunion, 2014).

H. coccineum can be found in similar habitats to its congener Hedychium gardnerianum, which has itself become a serious weed of native bushland, rainforests, closed forests, forest margins, watercourses and riparian habitats in countries where H. coccineum is also naturalized, such as in sub-tropical and warmer temperate regions of New Zealand; Hawaii, USA; South Africa; La Réunion, Africa; and Australia.

Infestations of H. coccineum have been reported in plantations in South Africa as well as limited access to plantations caused by the plant (Henderson, 2001).

Genetics

The chromosome number reported for H. coccineum is 2n = 68 (Flora of China Editorial Committee, 2014). Hedychium (x = 17) (Gao et al. 2008).

Mukherjee (1970) examined Hedychium species from India and reported a degree of correlation between leaf index and ploidy level, indicating that with the increase in the level of ploidy, there is also an increase in the leaf breadth and decrease in leaf length in the genus Hedychium. Accordingly, the diploid taxa have longer and narrower leaves in comparison to tetraploids which have shorter and broader leaves. While the stomatal size increases, their number per unit area decreases with the increase in ploidy level. H. coccineum (from Darjeeling) was found to be tetraploid and its chromosomes fall in 13 fours, 2 triplets and 5 pairs with 68 chromosomes agreeing with that reported in Flora of China Editorial Committee (2014). Mukherjee (1970) found the tetraploids to be erect, large with few tillers, small flowers and scarcely fragrant. However, number of flowers arising from elongate spikes has increased considerably. Flowers are fully fertile and they are probably alloploid in constitution. No positive correlation between level of ploidy and the useful properties like size and colour and extent of scent in flowers was detected.

Reproductive Biology

The scent of the flowers and the conspicuous petals indicate insect pollination, while the long exerted stamen and style suggest that hovering insects in particular may be involved. Reports of self-sterility dating back to 1900 are common for the genus (Holttum, 1950; Gao et al., 2008), with morphological individuals of the species appearing sterile between themselves despite hybridisation with other species of the same genus (Ludwig, 1900). Whilst this ready hybridization has contributed to the confusion surrounding the current taxonomy of Hedychium (Wood et al., 2000), it provides breeders with an opportunity to develop many new cultivars. Failed cross-fertilization of a Javanese H. coccineum with plants introduced into Brazil has been reported for this species (Ludwig 1900). The structure and development of the inflorescence and flowers of H. coccineum is described in detail in Kong et al. (2010).

Physiology and Phenology

In China, this species has been recorded flowering from June to August and fruiting in October (Flora of China, 2016). Peak bloom occurs in early to mid-summer in zones of the United States, but a few blooms may appear in the late summer to autumn months on late-emerging canes. In South Africa, it flowers from January to March.

The chemical composition of the essential oils obtained from the hydrodistillation of the rhizomes of H. coccineum grown in Mauritius was investigated by GC and GC/MS. The oils were characterized as follows: H. coccineum: (E)-nerolidol (44.4%), trans-sesquisabinene hydrate (24.2%) (Gurib-Fakima et al., 2002).

Associations

H. coccineum attracts hummingbirds in areas where it has been planted in Florida, USA (Dave’s Garden, 2014).

Environmental Requirements

H. coccineum prefers moist, wet and well-drained soil, but it is ecologically very versatile. It grows within an altitudinal range of 600 m-2300 m. It is recommended for USDA Zones 8-11 being evergreen at the warm end of the range and grown as a deciduous perennial in colder zones. It prefers a warm, frost-free climate although it will grow outside in temperate areas that have light, infrequent frosts. Easily cultivated in gardens in temperate regions, it will tolerate full sun to light shade and is considered one of the hardier gingers (Branney, 2005).

Cercospora hedychii [Pseudocercospora hedychii] fungi was reported from the leaves of H. coccineum in Java, Indonesia (Bussaban, 2002; USDA-ARS, 2014). There are also records of Leptosphaeria sp. from Cuba occurring on H. coccineum (USDA-ARS, 2014).

Ben-Dov (2006) report H. coccineum as a host of the scale insect, Asterolecanium epidendri (Hemiptera order, Asterolecaniidae family).

Surveys across the Indian native range have provided an opportunity to observe natural enemies associated with a number of Hedychium species, including H. coccineum. In the state of Meghalaya, surveys in the East Khasi Hills highlighted a number of damaging insect and pathogen species associated with the plant such as fungal leafspots and leaf folders (Lepidoptera) and leaf miners (Hispine beetles) (D Djeddour, CABI, Egham, personal observation, 2014).

Environmental

• Amenity
• Landscape improvement

General

• Botanical garden/zoo
• Ritual uses
• Sociocultural value

Materials

• Essential oils

Medicinal, pharmaceutical

• Source of medicine/pharmaceutical
• Traditional/folklore

Ornamental

• Cut flower
• Potted plant
• Propagation material
• Seed trade

Hedychium coccineum has extensive synonymy (see identity section); some of the variants in leaf shape and flower colour have been treated as botanical varieties or even elevated to species in their own right. It is often suggested that these should be lumped together making no attempt to distinguish botanical varieties. Several forms have long been in cultivation and plants imported from Indian nurseries may be crosses between several forms (Browse McMillan, 2004). Hedychium ’kewense’ and Hedychium ‘raffillii’ have been assigned to Hedychium × moorei (the H. coccineum × H. gardnerianum hybrid) but are very similar to H. coccineum which has resulted in their being treated under that species at various times.

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.

Monitoring and surveillance

In July 2013, interim regulations and invasive species lists were published under the National Environmental Management: Biodiversity Act (NEMBA), Act 10 of 2004, proposing new legislation for H. coccineum as NEMBA – Category 1b. These are invasive species requiring compulsory control as part of an invasive species control programme and deemed to have such a high invasive potential that infestations can qualify to be placed under a government sponsored invasive species management programme.

H. coccineum is listed on the invasive alien plant list for La Réunion as defined by the Conservatoire Botanique National de Mascarin (CBNM), a conservatory which is involved in the management and monitoring of species and populations in their natural habitats, including the study and control of invasive plants which are recognized as one of the major threats to island native floras (Hankamer & Maunders, 1998).

Public awareness

Likely to be greater in countries where the potential impact of environmental weeds is more familiar (e.g. Australia and South Africa) however the status of H. coccineum as a popular garden or landscaping plants can make its harmfulness a more difficult message to convey.

Eradication

No specific mention of control or eradication attempts for H. coccineum other than elimination of a few individuals detected in Bébour near the river des Marsouins in 2006 in La Réunion, France (Groupe Espèces Invasives de La Réunion, 2014).

Control

Control is patchy and given its invasive potential, small infestations should perhaps be prioritized for control before the problem escalates.

Cultural control

Non-invasive substitutes should be used in gardens.

Physical/mechanical control

Hand pulling recommended in the Giba Gorge Environmental Plan (Giba Gorge Environmental Precinct, 2011) – Conservation Management Plan for KwaZulu-Natal Sandstone Sourveld grasslands, Scarp forests, wetlands and cliffs of Kwazulu Natal, South Africa.

Biological control

None specifically for H. coccineum but a biocontrol initiative by CABI for a consortium of funders from New Zealand and Hawaii, USA, for Hedychium gardnerianum is ongoing and records/specimens of insects and diseases associated with all Hedychium congeners are being collected as part of the project (Djeddour D, CABI, personal observation, 2014).

Chemical Control

Currently, the most effective herbicide reported for the control of H. coccineum is metsulfuron, sprayed on the leaves, stems and root system. Foliar applications of glyphosate and root applications of imazapyr have also been recommended for the control of this species in Brazil (I3N-Brasil, 2016).

It is probable that the naturalized distribution of H. coccineum is under-represented and information on environmental and economic impacts is lacking, even in areas where the plant is recorded as a noxious invasive. It is an emerging weed which is hugely adaptable and still well traded worldwide. Congeneric species with similar growth habit and spread have become highly aggressive invaders in many regions of the world and the potential for H. coccineum to become notorious in its own right, or by hybridizing with other naturalized Hedychium species, is very high.

28/06/16 Updated by:

Julissa Rojas-Sandoval, Department of Botany-Smithsonian NMNH, Washington DC, USA

12/12/2014 Original text by:

Djamila Djeddour, CABI, UK