Lysichiton americanus
(American skunk cabbage)

Pictures

Picture	Title	Caption	Copyright
Title Habit Caption Lysichiton americanus (Western skunk cabbage). habit. Goodman Creek, Eugene, Oregon. April 2008. Copyright I, Martin Bravenboer, the copyright holder of this work, release this work into the public domain. This applies worldwide.	Habit	Lysichiton americanus (Western skunk cabbage). habit. Goodman Creek, Eugene, Oregon. April 2008.	I, Martin Bravenboer, the copyright holder of this work, release this work into the public domain. This applies worldwide.

Identity

Preferred Scientific Name

• Lysichiton americanus Hultén & H. St. John

Preferred Common Name

• American skunk cabbage

Other Scientific Names

• Lysichiton camtschatcensis auct. non (L.) Schott

International Common Names

• English: American skunk-cabbage; American yellow skunk cabbage; meadow cabbage; skunk cabbage; skunk weed; swamp cabbage; western skunk-cabbage; yellow arum; yellow skunk cabbage; yellow skunk-cabbage
• French: faux-arum; lysichite

Local Common Names

• Denmark: gul kaempecalla
• Estonia: Ameerika kevadvohk
• Finland: keltamajavankalla
• Germany: Amerikanischer Riesenaronstab; Amerikanischer Stinktierkohl; Gelbe scheinkalla; Gelber skunkkohl; Scheinkalla, Amerikanische
• Netherlands: moeraslantaarn; stinkdierkool
• Norway: skunk-kala
• Poland: tulejnik Amerykanski
• Sweden: Amerikansk skunkkalla; gul skunkkalla; skunkkalla
• USA: western skunk cabbage

EPPO code

• LSYAM (Lysichiton americanus)

Summary of Invasiveness

Lysichiton has a century long history of cultivation and introduction, though it has never been a very popular species grown on a large scale. Both the size of the plant, its habitat and the smell of the flowers prohibit popularity of full grown species for small gardens. Lysichiton has mostly been used in large scale gardens and ponds where it can “take care of itself”. It is known to spread slowly but surely. In some cases a brook might be overrun in about 40 years (AJW Rotteveel, Netherlands Plant Protection Service, personal communication, 2009); in the Netherlands it took about 50 years to establish a small but viable and locally spreading population. The history of invasion is similar in the Taunus mountains of Germany (König and Nawrath, 1992) and elsewhere in Europe.

These established populations are able to out-compete native vegetation and over time create a problem for biodiversity. The inaccessible habitat makes control and eradication excessively difficult and only possible for small populations (Alberternst and Nawrath, 2002), and this is confirmed by experience in the Netherlands.

Taxonomic Tree

• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Monocotyledonae
•                     Order: Arales
•                         Family: Araceae
•                             Genus: Lysichiton
•                                 Species: Lysichiton americanus

Notes on Taxonomy and Nomenclature

Lysichiton americanus is an easily recognised and highly ornamental plant that has been used outside its natural range in North America as an ornamental plant in ponds and brooks of large gardens. There is no information on races, cultivars or varieties; it is likely that the species has hardly deviated from the original wild species.

Lysichiton camtschatcensis is the only other species in the genus. It is closely related and was originally restricted to north-east Asia. It is also grown as an ornamental in the same habitats as L. americanus (Royal Horticultural Society, 2011). Stace (1991) comments that the two taxa hybridise, are often confused, and might be better treated as subspecies. The taxonomy of the two species is discussed by Armitage and Phillips (2011). They note that a hybrid between the two has been given the designation L. hortensiscv Billy.

The Jepson Flora Project (2001) discusses the historical anomalies in the spelling of the specific epithet “americanus”. The epithet “americanum” has been used as well, but is now considered wrong. The genus name Lysichitonis also misspelled on occasion asLysichitum.

Description

L. americanus is a tall herb (up to 1.5 m high, covering approximately 1 m² ground) with large (40-70 cm up to 1.5 m) glossy light green leaves coming from short thick fleshy rhizomes (up to 30 cm long and 2.5-5 cm diameter). The 1 to 2 (sometimes up to 4) inflorescences are surrounded by a showy bright yellow spathe up to 45 cm high, enclosing one fleshy, up to 25 cm long spadix carrying many flowers at the bottom. Flowers are small, yellowish green, often monoecious with female flowers below and male above (with generally 4, sometimes 6 stamens); bisexual flowers are also found. Flowers consist of generally 4, sometimes 6 free or fused sepals. They usually flower between March and May before leaves appear. The fruits are green berries at the end of the spadix, and mature in its natural range from June to early August. Flowering and fruiting are earlier in the native range as compared to northern and central Europe (Alberternst and Nawrath, 2002).

A picture of the seeds may be found in the Digital Seed Atlas of the Netherlands (2006).

Plant Type

Distribution

L. americanus is a species that is confined in its native distribution to the western part of North America. It reaches south to California (Calflora, 2005) but hardly crosses the Rocky Mountains, while to the north it reaches Alaska. The closely-related species L. camtschatcensis occupies the other side of the Bering Strait and neighbouring East Asia. The species is thought to originate in eastern Asia and have crossed the Bering land bridge during the late Tertiary (Pliocene/late Miocene). L. americanus has never reached the eastern half of North America; its ecological place in those parts is taken by Orontium (Nie Ze-Long et al., 2006).

In its native distribution it is a plant that is typical for a number of both shaded and open swamp communities.

The USDA Natural Resources Conservation Service states on its website that L. americanus is native to Alaska, British Columbia, Washington, Oregon, California, Montana, Idaho and Wyoming (USDA-NRCS, 2011).

L. americanus has been introduced throughout Europe; however, although it is not common in its introduced range, it may locally dominate vegetation. In addition to its introduced range shown in the distribution table, the literature also mentions common names in Estonian and Polish suggesting this species may also be of ornamental use in these countries.

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

Lysichiton is an attractive plant that was taken a century ago to Europe as an ornamental. The first date it was mentioned in Britain was 1901, dates of introduction are not known exactly for other European countries, but the picture emerges of ornamental use in all western, northern and possibly also central European countries before 1950.

As an ornamental it demands planting in large swampy garden areas and because of this it is typically found in parks and landscaped estates. It is grown and traded as a speciality plant on a considerable scale (see various plant finder guides, e.g. Royal Horticultural Society, 2004). The Dutch plant finder mentions 10 nurseries as suppliers of the species (Wortelboer and Luijken, 2003).

Risk of Introduction

L. americanus has been introduced via the horticulture pathway into many (water and swamp) gardens over a long time period and on a considerable scale in many European countries. In many cases introduction into the wild has been carried out on purpose (e.g. in Taunus in Germany) or via old swamp-nurseries that have been abandoned and returned to the wild. Alberternst and Nawrath (2002) mention the introduction of species into the wild by dumping of garden waste. This is a route known for many ornamentals; for L. americanus this remains to be seen. Only the corm can establish vegetatively, and it is sensitive to drying out. Seeds need to be introduced at the right place and time. Not too many gardens are adjacent to a suitable swamp.

Planting has led to naturalised populations in several European countries.

L. americanus is known as being a hardy plant and that will seed spontaneously. Therefore it is not surprising that it will become established on suitable sites. Seed production starts after about 5 years.

It seems that natural dissemination by animals does not play a significant role (as yet) in its introduced range. Spread is mainly by flowing water. 

Habitat

L. americanus has a rather wide ecological amplitude as long as the habitat is wet. It grows in shady forested bogs, in peatbogs, in swamps in full sun, and in shallow brooks with flowing water. It grows best in nutrient rich soils but may be found in association with Sphagnum (Klinkenberg, 2009).

Habitat List

Hosts/Species Affected

L. americanus is a large plant, emerging in early spring, with very large leaves forming large and dense clumps of vegetation. It may be quite competitive with native vegetation in its introduced range. Alberternst and Nawrath (2002) mention competition with Viola palustris and orchids.

Biology and Ecology

Genetics

Chromosome number: 2n=28 (Flora of North America Editorial Committee, 1993).

Reproductive Biology

The plant propagates by seed. Young plants take 3 to 6 years to flower for the first time. Flowering takes place in spring (late March to May). The large, shiny yellow flowers attract mainly flies due to the strong smell that is emitted during flowering; giving rise to the name of skunk cabbage. The flowers sit on a spike that will carry the berries when ripening. At that stage the spike bends over and finally lies on the ground.

The seeds need vernalization and will germinate the following spring, or exhibit dormancy that may last 6 years (Alberternst and Nawrath, 2002).

L. americanus is protogynous, with great seasonal variation in floral sex ratios. It is pollinated chiefly by a small staphylinid beetle (Pelecomalius testaceum), which was found most abundantly on male-phase inflorescences in southeast Alaska. Yellow spathes attracted more beetles than green ones, especially on male inflorescences. The gelatinous coat around the seed was found to impede local dispersal and to slow germination slightly, but had no detectable effect on seed predation, and had a possible deterrent effect on a pathogenic fungus (Willson and Hennon, 1997).

Physiology and Phenology

Being a plant of very wet growing conditions Lysichiton is well adapted to oxygen-poor conditions. The plant emerges in spring when the leaves start to emerge and the flower spikes appear.

Associations

In the wild Lysichiton is characteristic for a number of plant associations in the USA and Canada. The Washington natural heritage programme site shows two associations named after Lysichiton:

• Thuja plicata - Tsuga heterophylla / Lysichiton americanus / Sphagnum spp. forest
• Thuja plicata - Tsuga heterophylla / Lysichiton americanus forest
  (Lysichiton occupies patches of swamps in these forests).

Environmental Requirements

Soils should be very wet and may be temporarily submerged; the water-table being from 10 cm above to 10 cm below the surface being ideal (according to gardeners). Standing water and flowing waters are equally suitable. This means that both oxygen-poor as well as oxygen-rich conditions are acceptable. Lysichiton withstands nutrient-poor conditions, but thrives best in nutrient rich clay soils (Plantfiles, 2011).

Plantfiles (2011), a US gardeners site, states that pH values between 5.6 (acidic) and 7.5 (neutral) are suitable for cultivation. It provides also information on hardiness for the following USDA zones:

USDA Zone 4b: to -31.6 °C (-25 °F)
USDA Zone 5a: to -28.8 °C (-20 °F)
USDA Zone 5b: to -26.1 °C (-15 °F)
USDA Zone 6a: to -23.3 °C (-10 °F)
USDA Zone 6b: to -20.5 °C (-5 °F)
USDA Zone 7a: to -17.7 °C (0 °F)
USDA Zone 7b: to -14.9 °C (5 °F).

Climate

Notes on Natural Enemies

The most important natural enemies, at least in the early stages of development, are slugs. Slugs are frequently mentioned by gardeners as the most important problem in establishing seedlings. Herbivory from other species does not seem to play an important role, which is understandable because of the toxicity of the plant due to oxalic acid (Plants for a Future, 2011). Kibota and Courtney (1991) record occurrence of Drosophila magnaquinaria on L. americanus in Oregon, USA, but do not suggest that it causes significant harm.

Means of Movement and Dispersal

Movement and dispersal of this species compared to other invasive species is very slow. It takes decades to settle and dominate even small sites.

Natural Dispersal (Non-Biotic)

Natural spread is only by seed as the rhizomes are short, growing deep in the soil, and not spreading. Seeds are mainly spread by water, and to some extent by animals (Alaska Natural Heritage Program, 2002). Propagation by dividing rhizomes is possible under cultivation conditions.

Intentional Introduction

L. americanus is typically a species that is introduced intentionally for ornamental purposes into a new habitat and is able to spread locally by natural means. When the sites of introduction are close to, or part of natural habitats, local spread to nature reserves may occur. Equally important or possibly more important might be intentional planting in natural areas (“enhancement of nature” is a hobby for some people) (Alberternst and Nawrath, 2002).

Pathway Causes

Pathway Vectors

Economic Impact

The economic impact of invasion by and naturalisation of L. americanus should be considered negligible unless expressed in terms of effort involved in eradication campaigns. As the size of the infestations are still low the costs of the efforts are still low, unless measured on a cost per surface basis. In that case the costs are quite high because the labour required is high and action takes at least 5 years to carry out and terrain is normally inaccessible.

An infestation in the Netherlands consisted of a few hundred square metres of swamp and only a few dozen large plants and a few hundred seedlings. The eradication effort has taken since 2006 with an estimated 100 man-hours and is not expected to be complete before 2011 at the earliest. Experience in Germany and Switzerland indicates similar situations.

Environmental Impact

Impact on Biodiversity

Studies in Germany by König and Nawrath (1992) and Alberternst and Nawrath (2002) report displacement and local extinction of mosses like Aulacomnium palustre, Spaghnum species, vascular plants like Carex echinata, Viola palustris and orchid species.

Uses

L. americanus is rich in calcium oxalate, which is toxic and if consumed makes the mouth and digestive tract feel as though hundreds of needles are being stuck into it. However, calcium oxalate is easily destroyed by thoroughly cooking or drying the plant. Lysichiton was/is used in Native American cooking on the west coast. The tubers are rich in starch but need thorough preparation (Plants for a Future, 2011).

Economic Value

L. americanus is a valued ornamental plant that has a small but significant market via garden centres and growers of (semi) aquatic plants. The value of that market is not known. It is likely that Lysichiton is traded internationally as is the case with practically all ornamentals.

Social Benefit

L. americanus is an ornamental species grown “to please the eye” and has in this way a social benefit. In its native range it is used as a medicinal herb for a plethora of ailments (Johnson, 1999).

Uses List

General

• Ornamental

Detection and Inspection

L. americanus is often growing as an invasive in inaccessible places. Detection is difficult only because of this inaccesibility. First findings are seldom the result of a directed search, but mostly of chance by nature lovers and nature managers. The colourful large blooms with their penetrating smell often are a first indication of its presence.

Known infestations can be inspected on foot, but sometimes only during part of the year when waterlevels are suitable. Willow swamps can be quite tangled, making inspection an arduous creeping job in deep mud. Brooks can be equally hard to inspect.

Similarities to Other Species/Conditions

L. americanus is very similar in most respects to Lysichiton camtschatcensis. It is distinguished from the latter mainly by its bright yellow flowers, that are white in L. camtschatcensis. The latter species is also slightly smaller. Hybrids of the two species are found in cultivation and are characterized by a light yellow spathe (EPPO, 2006).

Prevention and Control

Prevention

Removing Lysichiton from trade would have an effect on availability to gardeners. However, the plant is already present in many (swamp) gardens and rarity might only enhance its desirability.

Early warning systems

Early detection outside cultivation is important and is dependant on botany-loving volunteers reporting their findings, an example of this is FLORON in the Netherlands.

Rapid response

It is important to find new infestations as early as possible in order to halt seed production and hence dissemination.

Public awareness

Educating the public on the dangers of dumping garden materials outside their gardens, and worse, on planting garden species in the natural environment is likely to be the most important preventive measure that can be taken. 

Eradication

All eradication efforts so far (in Germany, Switzerland, and the Netherlands) depend on manual removal of plants, including rhizomes. With small populations this might be feasible; however, this may take years because it has to be continued until the seedbank is exhausted. There are no reports of successfully completed eradication campaigns as yet but Rotteveel (2007) describes the early stages of an eradication effort in the Netherlands which suggested that laborious digging out of the rhizomes would eventually be effective. 

Containment/zoning

This does not seem to be necessary or possible. The species confines itself largely to the watershed where it has established itself, but seeds move freely with flowing water. 

Control

Physical/mechanical control

Available control reports all describe removal by hand as the method of choice. In doing so one has to take care that the underground corm is removed. This is often not easy because it may be deep in the swamp (over 30 cm) and hard to remove. After initial action several years of inspection and seedling removal are necessary.

Chemical control

No reports on control of invasive Lysichiton refer to chemical control. It is likely that chemical control would be efficacious, but equally it should be expected that chemical control would do considerable collateral damage to the sensitive aquatic environment. It is likely that chemical control has not been tried for this reason.

Gaps in Knowledge/Research Needs

The European Food Safety Authority (EFSA) (2007) studied the EPPO pest risk analysis on L. americanus and concluded that the species could not yet be given a quarantine status because there are several gaps in knowledge, especially on its invasive behaviour in its acquired range.

References

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Contributors

16/11/09 Original text by:

Ton Rotteveel, Plant Protection Service, P.O. Box 9102 6700, HC Wageningen, Netherlands

Distribution Maps