Species Orchid Society of

Western Australia (Inc)

It grows like a weed

How often have you heard the phrase "It grows like a weed!" Most often this expression means that the plant that is vigorous and easy to grow. But, conversely, a 'weed' is not something that we want in our orchid pots. However, a 'weed' is just a plant that is in the wrong place. It is not of itself a nuisance other than when it is out of its natural habitat where nature provides checks and balances in the form of predators, climatic conditions or soil types that restrict
unfettered growth and prevent it becoming a weed.

Patterson's Curse or as it is known in South Australia, Salvation Jane, Echium plantagineum , native to western and southern Europe (found from southern England south to Iberia and east to the Crimea), northern Africa, and southwestern Asia (east to Georgia) was introduced to Australia, South Africa and United States. It is now an invasive weed, and due to the high concentration of pyrrolizidine alkaloids in the shoot, it is poisonous to grazing livestock, especially those with a simple digestive system like horses. The toxins are cumulative in the liver, and death can result. It also blocks up cereal harvesting machinery.

There are many other examples of plants that have become weeds when introduced to an environment where they do not occur naturally. So it begs the questions, can this happen with orchids? In general, orchidaceae tend not to be weeds because they are highly adapted to their
environments and pollinators.

The WA Department of Agriculture and Food has a list of 'known weedy species'. There are two orchids on this list, Oeceoclades maculata and Spiranthes sinensis. While import of these species is prohibited, I was not able to find any information about local infestations of
concern that would lead to this listing.

There are other orchids which also have the potential to become weeds. Perhaps the best known local example is a South African orchid Monadenia bracteata (recently reclassified as Disa bracteata). This species apparently made its way to Australia on ships from South Africa in the 18th century and is now widespread in southwest WA and Victoria. While it is not a proclaimed species (a noxious weed) in either WA or Victoria, it has been identified as a new and emerging weed in the Wimmera district as it is considered to be a threat to the environment as it has the
potential to impact on native understorey flora, especially rare and endangered plants. It is particularly attracted to disturbed sites and will grow in all soil types and light conditions. An added issue is that this species is self-pollinating. We have this plant growing on our property In amongst the native grasses and Banksias.

A local example with which some of you may be familiar with is Cynorkis fastigiata from Comoro Islands, Mauritius, Madagascar, Reunion, and the Seychelles. This species turned up in plants brought in from the Eastern States in the media. A vigorous terrestrial species, it is readily pollinated by local insects, with wind-dispersed seed. Some years ago, many of us had this species growing in other orchid pots although I suspect that it is no longer a problem as we destroyed unwanted tubers when we repotted our plants.

In the United States, the broad-leaved Helleborine (Epipactis helleborine) is now causing serous concern as it becomes established in garden beds and lawns.

It was intentionally introduced from Europe and is now spreading throughout Michigan in lawns, flower beds and along driveways. This orchid's (syn Serapias helleborine) natural habitat is Europe and Africa through to China.

The Michigan State University has had many samples submitted by homeowners for identification and advice on removal.

Unfortunately (though an advantage to plants that become weeds), this orchid is also very vigorous, and will regrow from even small segments of root left in the ground.

 

 


Epipactis helleborine. Photo credit: Rebecca Finneran, MSUE


Source: http://7song.com/photos/629/191/Epipactis-helleborine-Weed-orchid.jpg

However, in a somewhat strange twist to this story, Epipactis helleborine is now
protected in UK as it is uncommon. This supports the notion that a weed is merely a plant growing outside its proper habitat.

Arundina graminifolia (syn Arundina bambusaefolia) also known as Kinata weed is an Asian terrestrial species that has shown potential to become a serious weed. This species has now colonised many new habitats including Hawaii (where we saw it on the big island in the Kilauea national park), Cook Islands, Guam, Fiji and Marshal Islands as well as Puerto Rico, Jamaica and Guadeloupe. It is very adaptable and rapidly takes over roadsides and any similarly cleared areas, crowding out local plant species. It is very vigorous and keikis from just below the raceme after flowering. It is not particular about its pollinators, and as a result, it is cited as invasive in many Pacific islands,

In a paper by Ms M Goosem on issues associated with control of weeds along major powerline routes in Queensland, she strongly recommends that a localised infestation of Arundina
bambusaefolia be removed as it has the potential to become as serious problem. She notes that it is a tall plant, and when blown over by the wind or knocked down, will readily regrow from any part of the stem in contact with the ground. The photo below shows an expanse of Arundina graminifolia adjacent to steam vents in Kilauea National Park .

In an article by Clifford and Kobayashi 2012, Naturalizing Orchids and the Hawaii Pacific Weed Risk Assessment System, the authors identify several exotic introduced orchid species that in their view pose a serious weed risk to Hawaii. These include Arundina graminifolia, Spathoglottis plicata, and Vanda tricolor. A major concern is the displacement of native plants that can occur through crowding out.

Ken Jones