Invasive non-native species are species of plants or animals that have been introduced to an area outside of their natural habitat. These species may be introduced deliberately such as plants that have been introduced for their aesthetic value, or accidentally, such as species that have arrived attached to boats or in the soil of other plants. If these species become established in the wild they can threaten native biodiversity, have adverse impacts on economic activity, and in some cases they can even impact human health. Unfortunately south Armagh is now home to many invasive non-native species that are having a negative impact on the biodiversity here. It is therefore important that we can recognise these species and report any sightings so they can be properly controlled.
Many invasive non-native aquatic plants are still sold in garden centres. It is important to look at the scientific name of the plants you are buying as some can be labelled incorrectly and you may end up accidentally introducing an invasive species to your garden.
More information about invasive aquatic plants is provided by the Be Plant Wise campaign.
To help prevent the spread of invasive species it is important to be careful when buying and planting anything in your garden and to follow codes of practice when disposing of any garden waste or after any water based activities. The removal of invasive species that have already become established can be much more difficult, and with some species such as Japanese Knotweed and Giant Hogweed specialist help is required. More information about management and prevention can be found on the NNSS or Invasive Species Ireland websites.
If you discover any invasive species in your garden and are unsure of what to do contact us at [email protected] or Tel: (0)330 137 4898.
Japanese Knotweed was introduced into gardens in the 19th century as an ornamental plant. It is a tall plant with green, leafy shoots that can be up to 2.5m tall and purple speckled stems that look like bamboo. The leaves are shaped like a shield with a flat base. In the summer it also has white flowers that grow in loose clusters while in winter it is more difficult to identify appearing as brown, leafless stems. It is most commonly found in urban areas, parks, river banks and waste ground. It can be particularly destructive if located near property, growing through concrete and in some cases reducing house prices when it is found in their gardens.
Giant Hogweed was also introduced in the late 19th century as an ornamental plant for large gardens. It can be identified by its size at up to 5m tall with blotchy stems, sharply serrated leaves , and white umbrella shaped flowers up to 80cm in width. It is mainly found by streams and rivers but can also be seen on waste ground. If you find hogweed DO NOT TOUCH IT as even small amounts of sap from this plant can cause severe blistering of the skin when exposed to sunlight.
Himalayan Balsam is an attractive plant that can grow up to 2m tall and has reddish coloured stems with slender, finely serrated leaves that grow in whorls of 3- 5. Its most characteristic feature is its pink-purple flowers with trumpet shaped petals. During winter these features can not be seen so it is much harder to identify, only recognisable by hay-like remains and short, distinctive roots. It is commonly found growing on river banks but may also be found in other damp areas where it causes problems by out-competing native riverbank plants for pollinators such as bumblebees.
Cherry Laurel was introduced in the 19th century by estate managers and landowners who planted it for its ornamental value. It is an evergreen shrub that can reach up to 7m tall, with thick, glossy, oval shaped leaves. These leaves contain cyanide so are poisonous to humans and many animals. It also produces small, white flowers on upright spikes which are followed in autumn by inedible cherry-like fruits. It is typically found in old estate gardens and parks where it grows in dense thickets and takes over.
Rhododendron was introduced in the 18th century as an ornamental plant. It is an evergreen shrub that can grow to 8m with dense branches and leathery, dull green leaves that grow in spirals at the end of the stem. Its flowers are purple in colour and grow in clusters, with each flower attached separately to a central stem by short stalks of equal length. The density of its branches creates problems for nearby plants as it blocks out any light. It is also known to poison the soil in the surrounding area meaning that it is the only thing that can grow there. As it is very shade tolerant it has adapted to many habitats including woodlands, gardens, rocky banks and stream sides.
Spanish bluebells are widely grown in gardens and commonly crossbreed with the native bluebell. This is a concern as it weakens the characteristics of the native species and produces a highly fertile hybrid. Spanish bluebells have broad leaves about 3cm wide and flowers all around an upright stem. The flowers are normally a paler blue than the native bluebell but pink and white coloured ones have also been seen. The anthers with the pollen can be found inside the flowers and are typically blue. These characteristics are important as the Spanish Bluebell can often be mistaken for the hybrid species. They can be found in gardens, woods and parks close to urban areas.
New Zealand Pigmyweed (Crassula helmsii)
New Zealand Pigmyweed is one of the more recently introduced invasive species and is commonly sold as an oxygenator for garden ponds. Its scientific name is Crassula helmsii but it can also be sold incorrectly as Crassula recurva, Tillaea recurva and Tillaea helmsii. It has stems that are about 1cm wide with 2cm long yellowish-green leaves in opposite pairs. In the summer it can also have small, singular white or pale pink flowers. It is typically found in ponds, lakes and canals forming a dense mat on the water’s surface where it is shallow and partially submerged in areas where the water is deeper. It is particularly problematic when it forms dense mats as this displaces other plants, affects drainage and can impact the ability to use the waterway for amenities.
Curly Waterweed (Lagarosiphon major)
Curly Waterweed is widely sold as a garden pond or aquarium plant. Its stems can grow to 3m long and are often totally submerged though sometimes shoots can reach the surface. The leaves are strongly curved and grow in spirals. It is mainly found in slow-flowing water such as ponds and lakes where it forms dense growths that shade out other aquatic species.
Parrot’s Feather (Myriophyllum aquaticum)
Parrot’s Feather has been grown in water gardens since the late 19th century and can still be found in some garden centres under the name above or as Brazilian Water-Milfoil. It is a blue-green colour with feather-like, finely divided leaves that form in whorls of 4-6. Most of the plant is often submerged with the underwater leaves appearing more separated than those above the water. It normally occurs in ponds and canals and is known to contribute to flooding as it blocks drainage.
Floating Pennywort (Hydrocotyle ranunculoides)
Floating Pennywort, also called Water Pennywort or just Pennywort, is sold as a garden pond plant and has become established in the wild due to the improper disposal of plants that are no longer wanted. It has shiny, kidney-shaped leaves with a crinkled edge that can be up to 7cm wide. The leaves can float on the surface or emerge from it with fleshy stalks attached to them. It is normally recorded in slow-flowing water such as canals, lakes or ponds. Like many other invasive aquatic species it forms dense mats that can restrict water flow and affect amenity use.
Water Fern (Azolla filiculoides)
Water Fern or Fairy Fern as it is also known, was introduced as a decorative plant for ponds and aquaria. This plant is free-floating and is very small with rough leaves around 2.5cm long that are normally green with a reddish tinge. Black or brown roots may hang below the floating leaves and can be broken off easily. It is typically seen in ponds, lakes, canals and slow-flowing rivers where it can cause deoxygenation and block out light meaning other species in the area struggle to survive. It can also be a health hazard as its dense cover can sometimes make the water surface appear solid.
In the late 19th and early 20th century grey squirrels were deliberately released at some sites in Ireland intended to be a positive addition to the native biodiversity. They have since rapidly spread across the whole country and have contributed to a decline in the native red squirrel population. This is partly due to the fact that they are carriers of the pox virus which does them no harm but can kill red squirrels within 14 days. Grey squirrels are similar to the red squirrel in shape with short front legs and a long bushy tail but they do not have the red squirrel’s long ear tufts and are much larger in size. They have mainly grey coloured bodies and tails but some may also have gingery-brown patches of fur. They are found in most woodlands but can also occur in gardens and other areas with trees.
Wild Boar may once have been native to Ireland but became extinct many years ago. The first recent recorded sighting was in 2009 and they have since been sighted in various locations across Ireland. Anyone who farms wild boar in Northern Ireland must be registered with the Department of Agriculture and Rural Development and the release of them into the wild is illegal under the Wildlife (Northern Ireland) Order 1985. They have a large head and front that lead to a smaller hind, with thick, coarse, often brown or black coloured hair. It is common for the hair on the ridge of their back to be longer than that on the rest of their body. Wild Boar can sometimes be aggressive so it is best not to approach them if you see one.
Farming mink for their fur became popular in the 1950s and continued until it was banned in Northern Ireland in 2003. However many mink were introduced to the wild during this time through escapes or deliberate releases. Mink are members of the weasel family and are semi-aquatic so are most commonly found by waterways. They have long bodies with a small pointed face, bushy tail and short legs. They are often dark brown or black in colour and can have white patches on their chin and belly. As predators of many species of native wildlife including ground-nesting birds, water voles and fish they have had a significant impact on their populations in areas where they are in large numbers.