Hedychium gardnerianum
(kahili ginger)

Pictures

Picture	Title	Caption	Copyright
Title Habit Caption Population of H. gardnerianum in the understory of native rainforest in La Réunion: capsules have fallen after fructification. Copyright Soudjata Radjassegarane	Habit	Population of H. gardnerianum in the understory of native rainforest in La Réunion: capsules have fallen after fructification.	Soudjata Radjassegarane
Title Habit Caption Population of H. gardnerianum in the understory of native rainforest in La Réunion: note one plant with capsules (orange) with some seeds (red) which attract birds. Copyright Soudjata Radjassegarane	Habit	Population of H. gardnerianum in the understory of native rainforest in La Réunion: note one plant with capsules (orange) with some seeds (red) which attract birds.	Soudjata Radjassegarane
Title Habit Caption Population of H. gardnerianum in the understory of native rainforest in La Réunion: vegetative stage of H. gardnerianum. Copyright Soudjata Radjassegarane	Habit	Population of H. gardnerianum in the understory of native rainforest in La Réunion: vegetative stage of H. gardnerianum.	Soudjata Radjassegarane
Title Flowers Caption Flowers of H. gardnerianum: inflorescence in clusters. Note yellow flowers with red stamens. Copyright Soudjata Radjassegarane	Flowers	Flowers of H. gardnerianum: inflorescence in clusters. Note yellow flowers with red stamens.	Soudjata Radjassegarane
Title Flower spikes Caption H. gardnerianum; flower spike and unopened bracts, India. Copyright Djamila Djeddour/CABI E-UK	Flower spikes	H. gardnerianum; flower spike and unopened bracts, India.	Djamila Djeddour/CABI E-UK
Title Fruithead Caption Fruithead of H. gardnerianum: mature fruits with orange capsules and bright red seeds that attract birds. Copyright Soudjata Radjassegarane	Fruithead	Fruithead of H. gardnerianum: mature fruits with orange capsules and bright red seeds that attract birds.	Soudjata Radjassegarane
Title Mature fruits Caption Mature fruits (green capsules) of H. gardnerianum. Copyright Soudjata Radjassegarane	Mature fruits	Mature fruits (green capsules) of H. gardnerianum.	Soudjata Radjassegarane
Title Avian seed dispersal Caption Action of birds in seed dispersal; fruits of H. gardnerianum (capsules open by three valves). Seeds have been eaten and thus dispersed by birds. Copyright Soudjata Radjassegarane	Avian seed dispersal	Action of birds in seed dispersal; fruits of H. gardnerianum (capsules open by three valves). Seeds have been eaten and thus dispersed by birds.	Soudjata Radjassegarane
Title Seedlings Caption Seedlings of H. gardnerianum in understory of native rainforest in La Réunion: note regeneration of endemic species of Réunion island (Chassalia corallioides, Rubiaceae). Copyright Soudjata Radjassegarane	Seedlings	Seedlings of H. gardnerianum in understory of native rainforest in La Réunion: note regeneration of endemic species of Réunion island (Chassalia corallioides, Rubiaceae).	Soudjata Radjassegarane
Title Rhizomes Caption Rhizome system of H. gardnerianum: note axillary bud. Copyright Soudjata Radjassegarane	Rhizomes	Rhizome system of H. gardnerianum: note axillary bud.	Soudjata Radjassegarane
Title Invasive habit Caption Dense H. gardnerianum infestation in Hawaiian forest. Copyright Pat Bily/The Nature Conservancy, Hawaii	Invasive habit	Dense H. gardnerianum infestation in Hawaiian forest.	Pat Bily/The Nature Conservancy, Hawaii
Title Invsasive habit Caption H. gardnerianum invasion in the Azores. Copyright Djamila Djeddour/CABI E-UK	Invsasive habit	H. gardnerianum invasion in the Azores.	Djamila Djeddour/CABI E-UK
Title Invasive habit Caption H. gardnerianum invasion in New Zealand. Copyright Jonathan Boow/Auckland Regional Council	Invasive habit	H. gardnerianum invasion in New Zealand.	Jonathan Boow/Auckland Regional Council
Title Control measures Caption Manual control of H. gardnerianum in Hawaii. Copyright Pat Bily/The Nature Conservancy, Hawaii	Control measures	Manual control of H. gardnerianum in Hawaii.	Pat Bily/The Nature Conservancy, Hawaii
Title Natural enemy Caption Stem boring weevil (Tetratopus sp.) on H. gardnerianum, Sikkim, India. Copyright Djamila Djeddour/CABI E-UK	Natural enemy	Stem boring weevil (Tetratopus sp.) on H. gardnerianum, Sikkim, India.	Djamila Djeddour/CABI E-UK

Identity

Preferred Scientific Name

• Hedychium gardnerianum Sheppard ex Ker Gawl.

Preferred Common Name

• kahili ginger

Other Scientific Names

• Hedychium glaucum Rosc.
• Hedychium pallidium Regel
• Hedychium var. pallidium Regel

International Common Names

• English: garland flower; ginger lily; kahila garland-lily; wild ginger; yellow ginger lily

Local Common Names

• China: jin jiang hua
• Cook Islands: kopi
• Fiji: cevuga dromodromo
• Germany: Girlandenblume
• Micronesia, Federated states of: sinter weitahta
• Nepal: sun kewara
• Netherlands: gardner's gember
• Portugal/Azores: conteira
• Réunion: le longose
• Saudi Arabia: longose
• USA/Hawaii: awapuhi kahili; cevuga dromodromo; kahili

EPPO code

• HEYGA (Hedychium gardnerianum)

Summary of Invasiveness

Native to the Eastern Himalayas, H. gardnerianum has been widely introduced as an ornamental in different regions of the world. It continues to be available as an ornamental and is therefore likely to spread further.H. gardnerianum is an ecologically versatile plant with rapid vegetative growth, the dense rhizome system of the plant prevents regeneration of other species. This very aggressive, shade-tolerant plant is able to form dense thickets on undisturbed sites in the understorey of open and closed-canopy native rain forests and managed forests, as well as in open areas (forest margins, ravines or path sides). Its high seed production and efficient dispersal by rats and birds, allows it to persist in invaded areas for a long time and establish new points of invasion. As H. gardnerianum is able to invade native forests, ecological, conservation and cultural values are threatened and it is a major threat to native biodiversity.

Taxonomic Tree

• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Monocotyledonae
•                     Order: Zingiberales
•                         Family: Zingiberaceae
•                             Genus: Hedychium
•                                 Species: Hedychium gardnerianum

Notes on Taxonomy and Nomenclature

Although there is little taxonomic confusion surrounding the species or its synonymy, several different taxonomic authorities are still used for Hedychium gardnerianum, including Ker Gawl. (Smith, 1983; Anderson and Gardner, 1999; PIER, 2000; ISSG, 2003), Roscoe (Hooker, 1897; Mitra, 1958; Cronk and Fuller, 1995; Missouri Botanical Gardens, 2003) and Sheppard ex Ker Gawl. (Stainton, 1988; Karthikeyan et al., 1989; USDA-NRCS, 2003) with reference to Sheppard, the publishing author, who did not provide the validating description. Sheppard is sometimes cited incorrectly as Shepard (e.g. USDA-NRCS, 2003). Randall (2002) and USDA-ARS (2003) use Sheppard ex Ker Gawl. as the taxonomic authority, which is accepted here.
 

Description

H. gardnerianum is a perennial herb with leafy shoots, 1-2 m tall, and large, branching surface rhizomes that may form dense mats up to 1 m thick. Leaves are alternate, ovate-elliptic, 25-45 cm long and 10-15 cm wide, subsessile, oblong, caudate, glabrous or sparsely pubescent along the midrib of the lower surface, apex short-acuminate, petioles 1-2 cm long, ligules membranous, 1.5-3 cm long, entire or very shallowly 2-lobed, glabrate, sheaths glabrous or glabrate. The flowers are scented and are bright yellow in colour. Inflorescences (spikes) erect, cylindrical, 25-40 cm long, primary bracts widely spaced, ovate-elliptic, spreading or obliquely ascending, much shorter than the floral tube, 1-2 flowered, 3-5 cm long, glabrous and pinkish inside, rachis glabrous; calyx cylindrical, 3-lobed, 3-3.5 cm long, greenish, reflexing; tube longer than the primary bract, 5-6 cm long, the lobes greenish yellow, linear, 3.5-5 cm long; labellum centrally tinged orange, 2.5-3 cm long; red stamens, far exceeding labellum, 6 cm long; lateral staminodes yellow, 3 cm long, narrowly oblanceolate; ovary glabrous, anthers orange-red, 0.8-1.2 cm, linear. After the flowers fall, the prominent fruiting spike remains, producing 1.5-2 cm long fleshy orange fruits: capsules persistent, oblong, 1.5 cm long, valves orange within each fruit contain small shiny red seeds included in a crimson arillus.

Plant Type

Distribution

H. gardnerianum is native to the Eastern Himalayas: India, Nepal, Sikkim, Khasia Hills (Hooker, 1897; Mitra, 1958), now widely introduced and naturalized in various tropical countries and probably present in areas neighbouring its native range. One of New Zealand's worst weeds of rainforests, a major weed of the Azores Islands of the mid-north Atlantic Ocean and also of Hawaii. It has been observed as widespread in Ecuador (Tye A, Charles Darwin Research Station, Galapagos, Ecuador, personal communication, 2003) though there is no specific literature record. First reported from Kruger National Park in 1999 (Foxcroft et al., 2008), it is a declared weed, naturalized and cultivated in South Africa.

Widely planted in Australia for its showy flowers, it is a weed of bushland, roadsides and riverbanks. In its very early stages of spread in Queensland, it has been highlighted as worthy of pre-emptive eradication (Blood, 2001).

It is probably far more widespread in tropical regions than indicated in the distribution table.

Distribution Table

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.

History of Introduction and Spread

First knowledge of this plant was derived from a dried specimen sent by Dr Nathaniel Wallich from Calcutta (1819) to the Botanic Garden at Liverpool, where it produced seeds and was subsequently introduced to greenhouses in the UK around 1823. Thought to have been discovered by Wallich in the valley of Kathmandoo, Nepal, he named this plant in honour of the Hon. Edward Gardner, son of the Admiral Lord Gardner, who lived in Nepal. H. gardnerianum has since been introduced throughout the tropics as a garden ornamental and is now invasive in many forest ecosystems (Cronk and Fuller, 1995), common in islands in the Caribbean, Pacific, Indian and Atlantic oceans, New Zealand and Natal, South Africa. It was introduced into New Zealand around the 1860s as a garden plant, and by the 1940s had escaped from gardens and naturalized in the wild along roadsides, bush fringes and stream edges from rhizomes and root fragments disposed of by gardeners. It is common in North Auckland, very common in and around Auckland City, common in Coromandel Peninsula, Kawhia, Bay of Plenty, Opotiki and Gisborne City, and in the Nelson-Buller area in South Island.

It was introduced to Réunion Island in 1819 (de Cordemoy, 1895) where it was for a while cultivated for the extraction of its essence.

In Hawaii, it was introduced as an ornamental before 1943 (Minden et al., 2010) and first collected in 1954 at Hawaii Volcanoes National Park (Smith, 1985) where it now covers over 500 ha (Anderson and Gardner, 1999). It is aggressive in wet, disturbed, well lit areas such as open-canopied forest understory and along streambeds and an especially large population occurs along the Koukouai stream in southwestern Kipahulu Valley (1070-1100 m) (Loope et al., 1992). Populations are now found on all islands in Hawaii (Smith, 1985) and it threatens undisturbed sites in the understory of open and closed canopy rain forests as well as in open habitats and forest edges around the National Park.

Introduced as an ornamental to São Miguel Island in the nineteenth century, it has become a dominant plant capable of replacing native vegetation and is naturalized on all the Azores Islands. It is present along stream margins and in the native vegetation from sea level to 1000 m (Cordeiro and Silva, 2003). Cutting of native forest for plantation is often followed by a potent invasion of H. gardnerianum (Cordeiro and Silva, 2003).

Risk of Introduction

Further spread is highly probable, owing to the risks of both accidental movement as a seed contaminant of crop seed and other agricultural produce, and deliberate introduction as an ornamental. This is encouraged by availability from commercial nurseries by mail-order catalogues and websites, for example, in France, La Réunion and the Netherlands. H. gardnerianum is one of the top 100 worst invasive species of the world (PIER, 2000). There are no regulations in La Réunion, but H. gardnerianum is prohibited as a noxious weed in New Zealand and it is a proscribed species to be intercepted at entry points to New Zealand and Hawaii.

In South Africa, it is a declared weed of forests, plantations, riverbanks and moist shaded sites (Category 1 plants): “These are prohibited plants that will no longer be tolerated, neither in rural nor urban areas, except with the written permission of the executive officer or in an approved biocontrol reserve. 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”.

Habitat

H. gardnerianum is native to the foothills of the Eastern Himalayas, in cool mountains areas at an altitude of 1200-2500 m, with a sub-tropical climate, cool winters and mild summers. It is present in forests and woodlands as an understorey species. It has been introduced to gardens as an ornamental, and escaped from these foci, especially along roadsides and stream edges, and is also a weed of natural forests, ravine sides, rail and roadsides, also wetlands and wastelands.
 

Habitat List

Hosts/Species Affected

Growth Stages

Biology and Ecology

Genetics

A spontaneous naturalizing hybrid (H. coronarium x H. gardnerianum= H. sadlerianum) is thought to have been found in Medeiros, Haleakala National Park Maui, Hawaii which favours the simultaneous seed production of H. gardnerianum (P Bily, The Nature Conservancy, USA, personal communication, 2008). Other interspecific hybridization may be possible and a natural hybrid of “Tara” (form of H. coccineum) and H. gardneriaum is postulated as the two species coexist in Nepal (PIER, 2007).

Physiology and Phenology

The flowering period occurs from December to March in La Réunion and after fructification in April to August, the above-ground parts of the plant senesce and die. A new stem will grow from an axillary bud present in the rhizome. In its native range, H. gardnerianum flowers and fruits from July to December.

Reproductive Biology

H. gardnerianum spreads primarily by vegetative regeneration of rhizomes: it can reproduce from any underground parts of the plant, even from the smallest root fragments and disperse as parts detach from the main plant. H. gardnerianum produces conspicuous and fleshy red seeds which are carried long distances by frugivorous birds and rats, creating many new infestation sites, making H. gardnerianum a far greater threat to native plant ecosystems and exotic forests. In the Azores, a study of seed production and vegetative growth on São Miguel revealed that the number of seeds per spike ranged from 300 to 500 and concurred with the findings of Byrne (1992), which ranged from 20 to 600 depending on light conditions. H. gardnerianum seeds do not have dormancy (Cordeiro, 2001) and only remain viable in the soil for a short period, relying on high annual seed production as a mechanism for efficient dispersal. Each new corm usually originates new leaves and eventually a spike although many act as storage organs and lack leaves. Generally, the pseudostem, leaves and spike collapse in winter leaving a scar at the top of the corm. Vegetative growth is characterized by the development of new corms at the rhizome ends, creating a dense cover and crowding the soil, which is how it impairs regeneration of native species.

The scent of the flowers and the conspicuous petals and petaloid staminodes indicate insect pollination, while the long exerted stamen and style suggest that hovering insects in particular may be involved. Wing scales of Lepidoptera have been found adhering to stigmas of some Hedychium spp. in their native habitats and it is likely that long tongued butterflies in search of nectar produced by the prominent gland at the base of the style are likely to brush the stigma followed by the anther-cells with their wings and carry out cross pollination.

Environmental Requirements

H. gardnerianum prefers moist, wet and well-drained soil, but it is ecologically very versatile, thriving in bright light or dense shade, good or poor drainage, high or low fertility, thick humus or very little soil, even sprouting in tree forks above the ground and on tree trunks, like epiphytes in the native rainforest in La Réunion. In La Réunion, H. gardnerianum is present in wetlands with annual rainfall of 2000-5000 mm, and with an annual average temperature range between 11°C and 17°C (Cadet, 1977). It generally occurs at altitudes of 800-2000 m in the native wet forests and disturbed areas. In Hawaii, populations are found on all islands between sea level and 1700 m (Smith, 1985).

 

Climate

Latitude/Altitude Ranges

Air Temperature

Rainfall

Rainfall Regime

Notes on Natural Enemies

Winks et al. (2007) reported the results of a survey for the fungi, bacteria and invertebrate fauna associated with H. gardnerianum carried out in New Zealand in order to identify and assess their potential as biological control agents. However, no specialist invertebrates or pathogens were found and most of the foliar damage caused was minimal and associated with generalist herbivores. In Hawaii, the soil-borne plant pathogenic bacterium, Ralstonia solanacearum, was isolated from a number of ginger species including H. gardnerianum. It caused a significant bacterial wilt disease and is spread naturally via soil water and root-root transmission, as well as artificially through wounds and agricultural practices. The bacterial survey in New Zealand did not detect any isolates of R. solanacearum, or any other plant pathogenic bacterium of wild ginger.

A number of fungi have been recorded from Hedychium spp. and a search of herbarium and fungal databases lists the following on H. gardnerianum: Microthyriella azorica, Gliomastix luzulae and Phomopsioides natalinae from the Azores, Stachybotrys subsimplex from Canada, Antennularia sp. from Jamaica, and a Mycosphaerella sp. from its native range in India (CABI, 2007; USDA-ARS, 2008). Periconia minutissima and Stachybotrys subsimplex from New Zealand; Pythium sp. and Rhizoctonia (root rot) from Hawaii. Note that mycobiota associated with the plant in its introduced range would either represent host shifts or would have been introduced on the plant as they were imported.

Means of Movement and Dispersal

The spread of H. gardnerianum is mainly furthered by its seeds, which are produced in very large numbers, eaten by frugivorous exotic birds and rats (e.g. Acridotheres tristis (mynah bird) and tui in New Zealand; Turdus merula azorensis in the Azores). This mechanism allows both short- and long-distance transport of the seeds. Seeds collected by birds may be eaten where they are found or transported and the seeds will be ejected some distance from the parent tree and will not impair germination. Such long-distance seed dispersal by animals appears to be the most effective method for establishing new points ('foci') of invasion. Each new colony also increases the size of the expanding margin of the invasion of H. gardnerianum by means of rhizomes, which can also be broken off and spread by water. Dispersal may also occur by hydrochory (rain water flushing of seeds and corms) over short distances (Cordeiro and Silva, 2003).

H. gardnerianum is used by man for ornamental purposes; several horticulturists sell rhizomes or plants of H. gardnerianum. Such introduction is encouraged by the availability of seed from the horticultural industry via mail-order catalogues; and as such, deliberate introduction of H. gardnerianum is quite likely.

Pathway Causes

Pathway Vectors

Plant Trade

Impact Summary

Economic Impact

There are no records of direct impact on crops, but mechanical and chemical control of H. gardnerianum is very costly.

A combined assessment of the estimated annual expenditure on kahili ginger control in the Hawaiian Islands of Kauai, Oahu, Maui and Hawaii come close to US $1 million, with approximately 50,000 acres estimated to be infested, although this is certainly an underestimate that doesn't include the full range of invading outlier populations (P Bily, The Nature Conservancy, USA, personal communication, 2008).

Environmental Impact

Although rhizome beds may become very deep, H. gardnerianum roots are quite shallow and maintain poor purchase in the soil. In steep areas, prolonged rainfall causes these rhizome beds to become heavy with absorbed water and the soil to become slip-prone. The combined effect of added weight, slip-prone soil and weak roots often leads to erosion, with entire hillsides of H. gardnerianum disappearing at once. Erosion also downgrades water quality and causes siltation of rivers and harbours. H. gardnerianum produce thick beds of rhizomes, forming a dense ground cover which prevents regeneration of other species. It spreads into shaded areas on native or managed forests and displaces lower tier plants of the native communities. This greatly impairs the regeneration of forests and proper functioning of ecosystems: H. gardnerianum threatens the biodiversity of native, undisturbed ecosystems. Studies by Minden et al. (2010) have shown that with removal of H. gardnerianum, however, the native Hawaiin forest is likely to regenerate and regain its natural structure.

In Hawaii, areas between sea level and 2300 m where the annual rainfall exceeds 1500 mm, the land below 1350 m has been greatly altered by agriculture. The gullies at these lower altitudes are forested by a tropical weed flora and between 1000 and 1650 m ginger creates significant problems, able to invade and take over native ecosystems without any apparent disturbance (Smith, 1985), preventing regeneration and threatening viability. Aircraft based analysis has found it to reduce the amount of nitrogen in the native Metrosideros polymorpha rainforests which have an impact on the natural ecosystem processes and can alter the type of fauna able to inhabit such habitat (ISSG, 2006).

Impact: Biodiversity

H. gardnerianum competes with native flora and disturbed native ecosystems and threatens biodiversity (Macdonald et al., 1991). It out-competes other species for light, space, nutrients and moisture and its shade tolerance makes it able to thrive in forests. Other invasive characteristics include rapid growth, long-term persistence of plants and ability to recover from removal of stems, making slashing worthless as a control measure. H. gardnerianum produces thick beds of rhizomes, forming a dense ground cover, which prevents seedlings of other plants from growing through them. The stems and leaves also form dense thickets, preventing other species from germinating below or growing amongst them. H. gardnerianum threatens remnants of primary forests of La Réunion. In the Azores, continuous expansion also threatens several fragments of endemic vegetation, leading to the prediction that several communities of lichens, vascular plants, molluscs, and arthropods native and endemic to the Azores
might be endangered, particularly on the islands of São Miguel, Santa Maria and Flores. Recent studies (Borges et al., unpublished data) suggest that for several endemic species of arthropods with a wide distribution in the Azores the smallest population densities are found in fragments disturbed by exotic plants. Also of concern is the present situation of H. gardnerianum in Terceira island, since it is now present in small gaps in the middle of large fragments of otherwise pristine native forest. Infestations on Sao Miguel Island also threaten the Azores bullfinch which is restricted to threatened natural laurel scrub and forest. The Madeira archipelago supports remnants of a type of laurel forest ("laurisilva" or "lauraceas madeirense") which is a protected area towards the higher altitudes that was once widespread throughout southern Europe and north-western Africa. The flora and fauna of this relict forest is quite unique; it has many endemic species including the Madeiran long-toed wood pigeon (Columba trocaz) and Zino's petrel (Pterodroma madeira). Having suffered extensive clearance after the islands were settled, the native vegetation is currently threatened by invasive species and the laurisilva forest, recently declared World Nature Heritage under the aegis of UNESCO is under serious threat due in particular to H. gardnerianum, which recently went into its colonization phase in new and extensive areas and can also impedethe natural expansion of laurisilva on abandoned rural land. Bird density and vegetation characteristics were studied in wet montane forest in native Hawaiian forests dominated by Metrosideros polymorpha at the summit of Kilauea Volcano, on plots containing greater than 90% ginger invasion and on plots from which ginger was eradicated. Results supported the hypothesis that species less dependent on native fruiting plants in the understorey will remain unaffected or possibly augmented (Apapane and Japanese white-eye), but did not support the hypothesis that ginger invasion decreases the density of understorey feeding birds.

H. gardnerianum is a threat to Labordia tinifolia var. lanaiensis and Clermontia samuelii in Hawaii (PIER, 2007).

Threatened Species

Social Impact

Risk and Impact Factors

• Proved invasive outside its native range
• Highly adaptable to different environments
• Is a habitat generalist
• Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
• Pioneering in disturbed areas
• Tolerant of shade
• Long lived
• Fast growing
• Has high reproductive potential
• Reproduces asexually
• Has high genetic variability

• Altered trophic level
• Damaged ecosystem services
• Ecosystem change/ habitat alteration
• Modification of fire regime
• Modification of nutrient regime
• Modification of successional patterns
• Monoculture formation
• Negatively impacts cultural/traditional practices
• Negatively impacts forestry
• Negatively impacts livelihoods
• Reduced amenity values
• Reduced native biodiversity
• Threat to/ loss of endangered species
• Threat to/ loss of native species

• Competition - monopolizing resources
• Competition - shading
• Competition - smothering
• Competition
• Hybridization
• Rapid growth

• Highly likely to be transported internationally deliberately
• Highly likely to be transported internationally illegally
• Difficult/costly to control

Uses

H. gardnerianum has been introduced all over the world as an ornamental because of its beautiful and fragrant flowers. It is still available via the Internet from horticulturist websites. H. gardnerianum was cultivated for the extraction of its essence in La Réunion in the 1930s and was later abandoned. The essential oil from the rhizomes of H. gardnerianum contains 30% sesquiterpenes (Weyerstahl et al., 1998).
 

Uses List

Environmental

• Amenity
• Landscape improvement

Fuels

• Fuelwood

General

• Botanical garden/zoo
• Capital accumulation
• Ritual uses

Materials

• Fibre
• Oils

Medicinal, pharmaceutical

• Source of medicine/pharmaceutical
• Traditional/folklore

Ornamental

• Cut flower
• Propagation material
• Seed trade

Similarities to Other Species/Conditions

Four Hedychium species are very common and can be distinguished by the colour of their flowers. H. coccineum has red or reddish orange flowers, and has more slender upright leaves. H. coronarium has white flowers which are sweetly fragrant. H. flavescens leaves are slightly narrower than those of H. gardnerianum. The flower head, 10-15 cm long, is also much smaller. Its fragrant flowers are creamy-white to pale yellow with yellow stamens. Flowers of H. flavescens do not produce seeds but it spreads relatively quickly by vegetative regeneration of rhizomes. H. flavescens is a major invader of native forests in New Zealand (Auckland Regional Council, 1999) and is also invasive in La Réunion: it is present in wet areas such as ravine sides, roadsides, native forest margins and disturbed forests (Radjassegarane, 1999). In Hawaii, H. flavescens and H. coronarium are weedy although these are usually confined to forest edges instead of invading the understorey.

Prevention and Control

Control

Mechanical control

Hand pulling can be effective on young seedlings. Small populations may be dug out and all underground parts must be removed. In La Réunion, mechanical cutting is frequently used to clear forest understorey, forests margins and ravines or roadsides. This method provides no long-term control but slows down its propagation and spread. Cutting before flowering (December to April, in La Réunion) is more effective in reducing seed production. H. gardnerianum inflorescences can be cut and dropped on the ground prior to the seeds being formed: this removal will not kill the plant but it will stop it seeding. The National Biological Invasions research programme INVABIO in La Réunion was launched in 2000 by the French Ministry of Environment, and as part of this, a 3-year research project began in 2002 with the aim of studying the impacts of mechanical control measures on native biodiversity and dynamics of native communities. The results clearly showed that the removal of an invasive alien species causes modifications to the biodiversity and a quick return to the initial situation. Contrary to the results expected, the negative impacts on the ecosystem were numerous. From an economic point of view, the intervention was both very expensive (the removal of 70 T / ha of H. gardnerianum was estimated at 24,062 euros) and constrained (specialised workers, steep slopes, etc.). By contrast, non-intervention caused few disturbances. In the case of the very low-invaded native ecosystems, the recommendation for non-intervention and the least disturbance as possible is made when the ecosystem is little invaded, or invasion is recent, or the invasive alien species occupies a small area, then early detection and rapid eradication are of interest (preventive action) (Lavergne, 2005).

Chemical control

A number of herbicides have been investigated and used in the past 20 years for control of H. gardnerianum (Harris et al., 1996). Currently, the most effective herbicide reported for H. gardnerianum control is metsulfuron, sprayed on the leaves, stems and root system. The effects are noticeable after 3 months and the weed will die and its rhizomes will rot after 12 to 15 months (Auckland Regional Council, 1999). Glyphosate and amitrole are also used in New Zealand (Timmins and Mackenzie, 1995). Probably the most effective and cost-efficient control method is stump treatment with herbicide. The stems are cut close to the ground, just above the pink-coloured swelling at the stem base, and concentrated herbicide is applied to the freshly cut stump; glyphosate is the common herbicide for this in La Réunion. Due to the widespread distribution of H. gardnerianum, chemical control is more cost effective than manual or mechanical control. In Hawaii, unpublished research found that metsulfuron at 0.04lb/acre, imazapyr at 0.7lb/acre, and amitrol at 0.7lb/acre applied to visible rhizomes after mechanical clearing of top growth was very effective. A commercial mixture of 2,4-D + triclopyr was ineffective but 20% triclopyr ester product applied in straight stream to the stems and surface rhizomes provided 100% kill on Maui (Motooka et al., 2003).

Biological control

Chemical and mechanical control of wild ginger are labour intensive, expensive, time consuming and often ineffective, and environmental concerns such as soil leaching, ground water contamination often limit the usefulness of herbicides in some areas. Biological control is now considered the only practical approach for the long-term management of large H. gardnerianum infestations in native forests (Harris et al., 1996). 

Ralstonia solanacearum, a naturally occurring bacterium in Hawaii, was tested for its efficacy as a bioherbicide in Hawaiian forests. The ability of this bacterium to cause severe disease in H. gardnerianum, together with its apparent lack of virulence in other ginger species seemed to indicate high potential as a biological control agent (Anderson and Gardner, 1999). Plants were inoculated with an aqueous suspension of the H. gardnerianum-infecting strain of the bacterium by stem injection or root wounding and all inoculated plants developed irreversible chlorosis and severe wilting 3-4 weeks following inoculation. Systemic infection also caused death and decay of rhizomes. Subsequently, further experiments were carried out on species of ginger to evaluate their susceptibility to R. solanacearum (Rs) race 4 (ginger strains) by several methods of inoculation, including tests to simulate natural infection. In contrast to the previous reports that Rs strains from kahili ginger (H. gardenarium), were non-pathogenic on ornamental gingers, the kahili ginger strain wilted both ornamental and edible ginger (Zingiber officinale) species within 21 days. The ability of Rs race 4 to infect many ginger species without wounding and to survive for long periods indicates that high risks will be incurred if the kahili ginger strain is inadvertently introduced from the forest reserves into ginger production areas. Conflicts of interest can often limit which plant species can be targeted for biocontrol however and ornamentals, such as ginger (Hedychium spp.), cannot be targeted for biocontrol in Hawaii because they are seen as being of high value to the Hawaiian tourist industry, despite their status as serious invaders of Hawaiian forest (Gardner et al.,1995).

In 2008, a scoping study to investigate the potential for classical biological control of the invasive Hedychium species was funded by a consortium of sponsors from Hawaii and New Zealand. Surveys in the native range (Eastern Himalayan foothills of India) identified a large guild of natural enemies exerting considerable pressure on H. gardnerianum  populations. The biological control project led by CABI scientists in collaboration with Government organisations in India is ongoing and research is now focused on prioritizing natural enemies for host specificity testing in the UK (D. Djeddour, CABI, pers. com., 2011).

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Links to Websites

Contributors

01/08/2008 Updated by:

Djamila Djeddour, CAB Europe - UK, Bakeham Lane, Egham, Surrey TW20 9TY, UK

Distribution Maps