Lysichiton americanus
(American skunk cabbage)

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.

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.

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. 

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).

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.

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).

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.

General

• Ornamental

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.

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).

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

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.

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.

16/11/09 Original text by:

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