While often chosen for their uniqueness and decorative qualities, certain species of plants introduced to the UK can pose serious risks to human and animal health.

According to the Norfolk Non-Native Species Initiative, here are six plants homeowners in the county should look out for on their land. 

1. Giant hogweed

Eastern Daily Press: Giant hogwood is a common sight in the UK but it hides a dangerous secret. Giant hogwood is a common sight in the UK but it hides a dangerous secret.

Giant hogweed produces a phototoxic sap that can cause severe burns and blistering when it comes in contact with skin and is exposed to sunlight.

The plant negatively impacts biodiversity by forming dense canopies which can shade out native vegetation and can burn pets such as cats and dogs as well.

As seeds are spread by wind and water, the Norfolk Non-Native Species Initiative advises eradication to take place annually to not let the plant seed. 

2. New Zealand pygmy weed/Australian swamp stonecrop

Eastern Daily Press: New Zealand pygmy weed creates a blanket of suffocating darkness.New Zealand pygmy weed creates a blanket of suffocating darkness. (Image: Jonathan Kington)

This plant group reproduces vegetatively by small fragments that can easily be spread on clothing or equipment or by animals - making it extremely difficult to contain. 

It forms dense mats on water bodies that shade out other aquatic vegetation which has a negative impact on fish and invertebrate life.

These mats of vegetation can impede drainage and lead to flooding so the use of herbicide in the isolated area is advised to completely eradicate the outbreak.

3. Floating pennywort

Eastern Daily Press: Floating pennywort - hydrocotyle ranunculoides - has been seen on the River Ant in the Norfolk Broads.Floating pennywort - hydrocotyle ranunculoides - has been seen on the River Ant in the Norfolk Broads. (Image: Archant)

These mats of floating vegetation have been observed to grow up to 20cm per day and can be so dense that dogs and other animals who fall in can potentially become trapped and drown underneath.

Pennywort often outcompetes native aquatic plants and clogs waterways which leads to the disruption of natural river processes.

It can increase the temperature of the water by absorbing sunlight which provides the perfect conditions for mosquito breeding sites.

4. Himalayan balsam

Eastern Daily Press: Norfolk Rivers Trust and the Norfolk Non-Native Species Initiative have launched a project aiming to eradicate Himalayan balsam from the River Wensum

This plant, introduced to the UK in the 1800s, produces a lot of nectar which bees and other pollinating insects prefer, leading to reduced seed production in native plant species and decreased biodiversity.

Each plant can produce around 800 seeds each year that are launched up to 7m from exploding seedpods.

The seeds can easily travel along watercourses which means this species can spread along rivers and streams which leaves the banks bare and susceptible to erosion.

Small infestations such as those found in gardens can be easily controlled by pulling out by hand due to the plant's shallow roots.

5. Japanese knotweed

Eastern Daily Press: Japanese knotweed causes an estimated £200m worth of damage in the UK every year.Japanese knotweed causes an estimated £200m worth of damage in the UK every year. (Image: Archant)

This infamous plant species have been known to grow through concrete pavements and building foundations, taking advantage of the smallest crack.

Damage caused by the species causes the UK an estimated £200m per year.

Removal of this species is highly controlled and should only be done by professionals in its more severe forms.

If you catch the outbreak early, you can treat it with a glyphosate-based herbicide to save yourself from a potentially very costly problem in the future. 

6. Parrot's feather

Eastern Daily Press: Pretty, but deadly. Parrot's feather starves waterways of sun and nutrients.Pretty, but deadly. Parrot's feather starves waterways of sun and nutrients. (Image: Evelyn Simak)

Similar to floating pennywort, parrot's feather can blanket a large area with weeds that choke waterways and prevent native plants and animals from accessing vital life systems. 

Parrot’s feather can also make rivers and lakes unsuitable for activities such as fishing and boating which the Norfolk Broads relies on.

Manual pulling of the plant can be an effective control method although it's best to contact a professional for safe removal. 

If you suspect you have any of these plants on your land, notify the Norfolk Non-Native Species Initiative so it can provide management advice as well as monitor the distribution of certain species.

To record a sighting, take a photo, note the date and location and any other additional information such as the abundance or size of the area and report online at NNNSI@norfolk.gov.uk.