Dangerous, Poisonous and Irritant Plant Species

Since setting up Jamie's Garden Services as a Grounds Maintenance business it has been a very interesting journey of learning many new skill. Rarely does a day go by without learning something new.

There are many dangers that are faced while undertaking such activities. Not just from using dangerous equipment, working at heigh or climbing trees.

It is surprising just how many plants can also pose a danger as well. I therefore thought that it would be interesting to create a page on my website that informs people about of some of the innocent looking plant that you may come across in every day life and not even knowing how dangerous they are to you.

These plants could be dangerous for many reasons, as they could be poisonous, cause skin irritation, infections,  cause a server reactions or burns as a result of coming into contact with them or their sap.

I hope that you enjoy reading this page..

Common Name:  Giant Hogweed

Botanical Name: Heracleum mantegazzianum

Description:  Looks like a giant version of Cow Parsley that you see on roadsides across the country.

Height: 2 to 5 m (6 ft 7 in to 16 ft 5 in) depending on its environment.

Danger:  Causes Skin Burns that Blister and re-blister when exposed to sunlight.
Areas affected: Gardens and allotments adjacent to infested woodland, heathland, common land wasteland.
Main Causes Sreading: Spreads by seed

Invasive: Spreads by seed
Timing:  Seen spring to autumn; treat in summer

Giant Hogweed (Botanical name: Heracleum Mantegazzianum)

Giant Hogweed is a relative of and looks very similar to an overgrown native Cow Parsley plant that is often seen along rural road verges and pathways. Please note that Cow Parsley can also grow to about 6ft, but is often seen when it is only 3-5 feet tall.  Hogweed is also a relative of the Carrot…  It is not unusual for Hogweed and Cow Parsley to occupy the same area

Identifying Giant Hogweed:

A giant hogweed is often very easy to identify because of its height. It grows vigorously in the early stages of its life. Other clues to identification are important, though, especially for a shorter or an immature plant. Some of these clues are listed below. 

The plant has:- Giant hogweed typically grows to heights of 2 to 5 m (6 ft 7 in to 16 ft 5 in) depending on its environment. - The Large leaves are incised / Serrated and deeply lobed. (Think of a Fat Cannabis type leaves). 

- A mature plant has huge leaves, between 1–1.5 m (3 ft 3 in–4 ft 11 in) wide, and a stout, bright green stem with extensive dark reddish-purple splotches and prominent coarse white hairs on the stem and especially at the base of the leaf stalk. These coarse white hairs can act like an injection and administering sap when touched. 

- Its hollow, ridged stems vary from 3–8 cm (1.2–3.1 in) in diameter, occasionally up to 10 cm (3.9 in) in diameter and can grow to more than 4 m (13 ft) high. (although the hollow stem element may not be obvious without breaking the stem and being exposed to the sap).

- Green Stems that often have Dark Red / Purple spots on the stem. 

- The Stems have Ridges and coarse hairs. 

- The umbrella-shaped inflorescence, called a compound umbel, may be up to 100 cm (39 in) in diameter across its flat top.  

- The flowers are white or greenish white and may be radially symmetrical or strongly bilaterally symmetrical (zygomorphic).  

- Small white flowers in a flattened or slightly domed cluster has up to fifty or more rays per flower cluster. - a flower cluster that is / can be as wide as two and a half feet.

- The fruits are schizocarps, producing seeds in dry, flattened, oval pairs. 

- Each seed is approximately 1 cm (0.39 in) in length, with a broadly rounded base and broad marginal ridges, tan in colour with brown lines (so-called oil tubes) extending 3/4 of the length of the seed. 

- It's important to remember that some plants in a species may have an atypical appearance. If you have any doubt about the identity of a plant, admire it from a distance and don't touch it.Heracleum Mantegazzianum: is also known as:  

- Cartwheel-Flower - Giant Cow Parsley  

- Giant Cow Parsnip - Hogsbane (In New Zealand).

- Wild Parsnip (not to be confused with Pastinaca sativa or wild rhubarb).

Although the plant is striking and can be attractive in certain situations, it was introduced to ornamental gardens in the 19th century from its native environment of Eastern Europe and Asia. Most gardeners will want to eradicate it, as it is potentially invasive and the sap can cause severe skin burns. It is widely distributed in the wild and poses a serious risk to people who are unaware of its potential for harm. Even if you are aware of the plant it is easy to be looking at the bigger more established plants and not realising that you are brushing past Hogweed leaves without its main stem that are closer to the ground. If you are wearing shorts you can guarantee that you could be brushing past them. This is why you need to steer clear of them and make sure your children also stay away. As they will normally love to run around and through them and they will often handle the stems.

There are about four other Giant Hogweeds in Britain some are biennial and others are perennial.Giant Hogweeds are usually referred to by one name, Heracleum Mantegazzianum. 

In Europe there are more than 20 species of the genus Heracleum that have been documented. Identification of Heracleum mantegazzianum is further complicated by the presence of two additional tall invasive hogweed species:  - Heracleum Sosnowskyi 

• Heracleum Persicum.  Other than size (as mentioned above), these species all have very similar characteristics.
• In Europe, Giant Hogweed look-alikes include:  - Hogweed (Heracleum sphondylium - Heracleum Sphondylium ssp sibiricum)- Wild Parsnip (Pastinaca sativa) - Garden Angelica (Angelica archangelica)  - Wild Angelica (Angelica sylvestris)

It is advised that all humans (especially children) should stay away from Giant Hogweed and Hogweeds in General. Extreme care should be taken when clearing areas of land and especially when using a strimmer because as the strimmer chord cuts through the plant, its sap can be sprayed all over the equipment operator. It is therefore import that people undertaking this type of work are wearing the correct PPE to protect them and this includes Eye & Face protection.

All of these Hogweeds pose a risk to public health because they have chemicals in their sap which cause phototoxic burning by making the skin sensitive and prevents the skin from protecting itself from sunlight (Phytophotodermatitis). A phototoxic reaction can begin as soon as 10-20 minutes after contact with the sap. Photosensitivity peaks between 30 minutes and two hours after contact but can last for several days and longer. It has been known to affect people for months in the worst cases.  The sap is contained in the Stork Stems, Leaves and even the roots  

Preventing and Dealing with Giant Hogweed Burns:  

The redness doesn't appear immediately. But once the discolouration does appear, it changes in appearance over time and can have a Dark Red / Brown colour. Skin often severely blisters and may also appear at some point and when the skin is exposed to sunlight after being affected re-blistering can also reoccur for even weeks, months and there are also claims that the skin can remain Phytophotodermatitis can last for many years with people reporting that the blisters reappear annually when the skin is exposed to sunlight. In some cases long-lasting scars may be also produced.  The sap is that dangerous if it gets in the eyes. It can cause severe eye irritation and even blindness. Reports vary in respect to whether the blindness is temporary or potentially permanent, but in either case it's a serious concern.

The Giant Hogweed shares these properties with its Heracleum relatives, such as the Cow Parsnip, and hence, similar caution is advised in handling these. Due to its shared physical similarities to the flower Queen Anne's Lace (Daucus Carota), it can therefore be easily mistaken as a harmless plant.

If a person does come into contact with hogweed sap, Urgent first aid procedures and aftercare are needed.- Avoid touching the eyes.- Immediately and thoroughly wash the area with plenty of soap and water. (This is the standard recommendation. Soap and water may not be available, however, so the area should be cleaned in whatever way is possible. The affected person should then head straight for the nearest source of soap and water.)- If you come in contact with the sap of the Giant Hogweed, immediately wash the affected area with lots of soap and cold water. Cover the area with layers of clothing or a material that blocks sunlight. Avoid further exposure to sunlight for at least 48 hours. It is also advised that you seek medical advice. - Medical attention is a must if the exposure or effect is widespread or severe. Important: Get medical aid immediately if sap has entered the eyes.

This is due to have high levels of Linear Furanocoumarins contained in the sap. It is thought that Furanocoumarins are produced by plants as a defence mechanism against predators such as insects and mammals. It is also likely that Furanocoumarins are related to a plant's natural defence against fungal attack.Hogweeds will affect areas like: Gardens and allotments adjacent to infested woodland, heathland or common land especially if it is not managed. The main causes of it spreading is by its seeds naturally being distributed. Hogweed is mostly seen between Spring and Autumn. If not treated each plant will spread its seed and before long you could have a Giant Hogweed Forest.

The best time of the year for treatment is in the summer. Glyphosate is often the ideal option, as is simply digging it out. Attention however must be paid in terms of completely covering hands, arms, face, legs, and wearing a mask if the plant is to be dug out. You do not want any part of your body / skin coming in to contact with the sap, so make sure your gloves are not absorbent and have a waterproof barrier. And extreme care must also be taken when handling gloves that have come in to contact with the plant.

Due to its phototoxicity and invasive nature, Giant Hogweed should be removed. In August 2017 the species was added to the List of Invasive Alien Species of Union concern. This placed restrictions on keeping, importing, selling, breeding and growing it and requiring governments to detect and eradicate it throughout the EU. In the UK, the Wildlife and Countryside Act 1981 (as amended) makes it an offence to plant or cause giant hogweed to grow in the wild.

Interesting Giant Hogweed Videos Worth Watching:Giant Hogweed & Cow Parsley, The Difference: https://www.youtube.com/watch?v=W9JNMR87ApQ  

Attack of the Giant Hogweed:https://www.youtube.com/watch?v=tQ9P1preCGM

Common Name:  Lords & Ladies

Botanical Name:   Arum Maculatum

Description:   Large Rich Deep Green Arrow-Head Leaves. The flower head tends to be small and hidden within the base of the beautiful ‘Cobra’ like hood. Arum flowers in Spring. The fruit / berries appear in Autumn, are dark red to orange and grow in a cluster on the erect flower stalk.

Height: 0.1m to 04m

Danger:   Poisonous/Irritant Plant: Toxicity All parts are highly toxic by ingestion and will cause irritation when coming into contact with the skin, Wear gloves and wash hands after handling

Areas affected: Wooded shaded areas

Main Causes Spreading: Root Stems

Invasive: Yes, Can be if not controlled

Timing:   March to November

Arum Maculatum has a number of common names:

- Lords and Ladies

- Devils and Angels

- Adam and Eve

- Cuckoo-pint

- Snakes Head

- Arum lily

Arum maculatum's habitat is a frequent sighted beside tree-lines river-side paths and shaded lanes as well as on edges of woodland, in scrub land and almost anywhere that is shaded and damp with nutrient-rich soil.

The flowers of Lords and Ladies open in April and May, and then the 'Cobra' hood decays leaving a stem on which berries develop and ripen in the Autumn.

Roasted roots of Arum maculatum were once used to produce a kind of drink. However, without the proper preparation the resulting beverage can be toxic. There is also a danger that young children might be tempted to eat the brightly coloured berries (although they are very bitter tasting), with serious consequences because this is such a poisonous plant.

Toxicity All parts are highly toxic by ingestion and will cause irritation when coming into contact with the skin, Wear gloves and wash hands after handling

The 'flower' of Lord and Ladies. Very common and while not strictly poisonous they contain oxalate crystals which are very sharp and can penetrate and irritate skin for a long time and if consumed can cause the throat to close.

The most common upset with Lords and Ladies is if somebody uses the leaves as woodland toilet paper, (Due to their size, thickness and locality) a mistake they will only make once!

Common Name:  Wolfsbane / Monkshood / Devil's Helmet

Botanical Name:  Aconitum napellus

Description: Blue, Purple, White, Yellow bell flower on tall stems, with dark green leaves. (Note slightly similar to the Foxgloves Plants)

Height: 3 to 5ft tall. 

Danger: Seriously Very Poisonous (One of the most toxic plants that can be found in the UK).

Areas affected:  Normally in mountainous area. Although it was once an ornamental garden plant.

Main Causes Spreading: Seed Dispersal.

Invasive: No

Timing:   Flowers in late Summer to early Autumn.

Monkshood, Wolfsbane, or Aconitum napellus, is the common known cure or weapon to use against the fantastical creatures, known as Werewolves. Though this isn't just a mythical plant whose only purpose is to fight these creatures of the night, it also contains many other dark and deadly secrets.

The neurotoxins, aconitine and mesaconitine can be absorbed through the skin and cause severe respiratory and cardiac problems.

This is a very poisonous plant. Aconitine, mesaconitine, hypaconitine and other alkaloids have potent cardiotoxins and neurotoxins that can be found in all parts of the Aconitum species, especially in the tubers and roots. The toxins can be absorbed through the skin and cause severe respiratory and cardiac problems.

The Latin name Aconite comes from the Greek ἀκόνιτον which means “without dust” and “without struggle”. It was used as a poison for arrow heads when hunting wolves (hence wolfsbane) and, as it is so fast acting, probably had them falling in the dust without a struggle.

Don't what ever you do, pick or handle this plant without gloves, especially by the root.

Common signs of monkshood poisoning include tingling, tongue and mouth go numb, nausea with vomiting, breathing becomes harder and laboured, pulse and heartbeat become weak and irregular, skin is cold and clammy. As the poisoning gets more severe, patients with internal (Aconitum) poisoning will begin to have cardiovascular (slows and stops the heart), neurological (pain, convulsions, paralysis), gastrointestinal symptoms (nausea and vomiting) and there are often other signs to look out for (example, confusion and mania can occur if the alkaloids reach the brain). Multiple organ failure is likely.

Although the leaves of the upper stem are particularly potent, with just a nibble being enough to cause death. The upper leaves of the stem are more dangerous than the lower leaves. Foxglove is most toxic just before the seeds ripen

So how deadly is Wolfsbane?

Marked symptoms may appear almost immediately, usually not later than one hour, and "with large doses death is almost instantaneous". Death usually occurs within two to six hours in fatal poisoning (20 to 40 ml of its toxin may prove fatal). 

Gardeners have been known to die from simply handling this plant.

Common Name:   Deadly Nightshade

Botanical Name: Atropa belladonna

Description:   Flowers are  bell-shaped with bright purple and green colouration, around 2.5–3cm in length, with leaves that are oval-shaped, un-toothed with smooth edges and pointed ends. They grow on stalks in an alternate pattern, reaching up to 7 inch in length, and are poisonous. Bearing shiny black berries with five sepals visible where the fruit attaches to the plant. The berries are also highly poisonous. 

Height:   6.6 ft (2 metres)

Danger:  Very Dangerous

Areas affected:  Woodland, Hedgerows, scrub, path edges. often found in the central and southern half of Britain on chalky soil and in areas where soil has been disturbed.

Main Causes Spreading: Seed Dispersal

Invasive: No

Timing:  Flowers and fruits from June to August.

Deadly nightshade has had a very will documented history, in both fiction and real life. Nightshade, together with Henbame and Mandrake have been linked to witchcraft.

Deadly nightshade was said to be the property of the Devil, meaning that anyone who eats the berries is punished for eating his fruit. 

As its name suggests, Deadly nightshade is a highly poisonous plant. Its black, shiny berries may be tempting to eat, especially for children, but fatal. The berries have a somewhat sweet taste and they are therefore tasty, which could encourage more to be eaten.

Found on chalky and disturbed ground, such as scrub, verges, pathways and hedgerows, it has bell-shaped purple flowers.

Medicines made from the plant are said to ease abdominal problems and motion sickness. It is also used by eye surgeons – in a very refined state because it dilates the pupils.

The name 'Belladonna' means ‘beautiful woman’ as it was used by Renaissance women to dilate their pupils. Atropa is in reference to Atropos, one of the Three Fates in Greek mythology who snipped the sting of a person’s life and decided their death.

Although the berries might be the most tempting to handle part of Deadly nightshade, all parts of this plant are poisonous if ingested. It causes a range of symptoms including blurred vision, a rash, headaches, slurred speech, hallucinations, convulsions and eventually death. As nightshade can grow as part of a hedge row with other edible fruit bearing plants.

The fruit berry at first are initially green but they ripen to a glossy, black berry is about 1.5 centimetres in diameter. The berries have a sweet taste and are attractive to animals / birds. They help disperse the seeds in their droppings, even though the seeds contain toxic tropane alkaloids.  

The most toxic part of the plant is the roots, but the alkaloids are to be found through the plant.  If bees feed upon its nectar, the honey produced will also contain the alkaloids!  Deadly nightshade is one of Europe's most toxic plants.

The active agents in deadly nightshade are tropane alkaloids (atropine, hyoscine (scopolamine), and hyoscyamine).

These chemicals have anticholinergic properties, This means that they block the action of the neurotransmitter - acetylcholine,  in the central nervous system. The effect of this is that the smooth muscle tissue of the gut and bladder is affected; heart and breathing rate are also affected, as are memory and learning.  The symptoms of poisoning with deadly nightshade include

• Dilated pupils, blurred vision,

• Loss of balance,

• Dry mouth and throat, slurred 

• The inability to urinate,  

• Confusion, hallucinations and delirium.

The alkaloids can, however, be put to good use.  Belladonna has long been used in medicine and in cosmetics.  Drops prepared from the plant were used to dilate women's pupils, an effect some considered to be attractive.  Atropine, one of the alkaloids is used for examination of the eye, it is also used as an antidote for organophosphate poisoning; scopolamine can be used in the treatment of gastro-intestinal complaints and motion sickness.

Common Name:   Foxglove

Botanical Name:  Digitalis purpurea

Description:  Purple, blue, white, lavender, yellow, pink, and red flower head on a tall stem with green leaves. The flowers have a condensed tower of heads, that will be of a single colour on the stem. 

Height:  6 feet (1.5m to 2.5 m.)

Danger:  Poisonous. 

Areas affected:  Gardens, Road side verges, Woodlands.

Main Causes Spreading:  

Invasive:  Not really

Timing:   Flowers in the main summer period.

Tall and elegant, Foxglove plants have long been included in garden areas where vertical interest and lovely brightly coloured flowers are desired. Foxglove flowers grow on stems which may reach 6 feet (2 m) in height, depending on the variety.

Foxgloves are native to Europe, western Asia, and northwestern Africa. The flowers are tubular in shape, produced on a tall spike, and vary in colour with species. There are about 20 species of herbaceous perennial plants, shrubs, and biennials, commonly called foxgloves.

The best-known species is the common foxglove, Digitalis purpurea. This a biennial, and is often grown as an ornamental plant due to its vivid flowers which range in colour

The term digitalis is also used for drug preparations that contain cardiac glycosides, particularly one called digoxin, extracted from various plants of this genus. Foxglove has medicinal uses but can also be toxic to humans and other animals.

Depending on the species, the digitalis plant may contain several deadly physiological and chemically related cardiac and steroidal glycosides. Thus, the digitalis plants have earned several, more sinister, names: dead man's bells and witch's gloves.

Foxglove plants contain the toxin Cardiac Glycosides. Ingestion of any parts of the plant can result in severe poisoning. Symptoms include nausea, headache, skin irritation and diarrhoea. In severe cases it can lead to visual and perceptual disturbances. Finally inflicting heart and kidney problems.

The Foxglove has also widely been used in folk medicine, and in conventional modern medicine, as their cardiac glycosides have been used to make a heart stimulant drug. 

Common Name:   Snake's-Head Fritillary

Botanical Name:  Fritillaria meleagris

Description:    Chequered, purple, pink or even white, bell-like flowers, nodding on thin stems. It has narrow, grey-green leaves that appear at the base of the plant and occasionally up the stem.

Height:  Up to 30cm

Danger:  Poisonous. 

Areas affected: Meadows, Wetlands, Commons, and River Banks.

Main Causes Spreading:  Self Seeding.

Invasive:  No. The plant is in decline.

Timing:   Flowers in April-May

The Snake's-Head Fritillary flower has a chequered pattern in shades of purple, or is sometimes pure white. It flowers from March to May and grows between 15–40 cm (6–16 in) in height. The plant has a button-shaped bulb, about 2 cm in diameter, containing poisonous alkaloids. It grows in grasslands in damp soils and river meadows at altitudes up to 800 m (2,625 ft).

Fritillaria meleagris is native to Europe and western Asia but in many places it is an endangered species  that is rarely found in the wild but is commonly grown in gardens. In Croatia, the flower is known as kockavica and is associated by some with the country's national symbol.

In the UK there is some disagreement amongst botanists as to whether F. meleagris is a native species or a long-established garden introduction from Eurpore.

The plant contains toxic alkaloids including Imperialine, which disrupts kidney and heart functions, and Tulipalin A, which causes a contact allergic reaction in the skin. Both toxins have been used in the development of pharmaceuticals.

Common Name:  Hemlock water-dropwort (Water Hemlock, Dead Mans Fingers, Dead Tongue) 

Botanical Name: Oenanthe crocata 

Description:  Leaves: Bright green and shiney, a bit fern like with two to four pinnate divisions, the whole looking triangular in shape.  

Flowers: A collection of small white flowers arranged in an umbel. 

Seeds: Small brown rugby ball shaped seeds in clusters replacing the flowers. 

Height:  1m to 1.5m

Danger: Very Dangerous / Poisonous 

Areas affected: Damp areas including marshes, lake, river and stream sides or along ditches. Can be found several meters inland from water sources. 

Main Causes Spreading: Wind and River Flow

Invasive: Easily Spreads along river banks 

Timing:  February to July

One of the The most poisonous plants in the UK and very common along most of our waterways.  

The main toxic constituent of hemlock water dropwort is Oenanthotoxin. The concentration of this poison in the plant roots is highest in winter and spring and ingestion of very small amounts may prove fatal. These events occurred in April when the concentration of toxin is still highest. 

The term sardonic grin comes from the grisley practice in Phoenician Sardinia of disposing of criminals and old people using Hemlock Water Dropwort. The poison acts by constricting the muscles causing death by asphixia which also causes a rictus like death grin, the sardonic grin.  

Hemlock Water Dropwort is one of the most poisonous plant in the UK and all parts of it are poisonous, it is reported that death can occur in as little as a couple of hours after ingestion.  

WARNING: It is possible to confuse Hemlock water-dropwort with Flat Leaved Parsley, Water Parsnip or Water Celery. Especially as it smell like very sweet parsley, its lovely smell gives no indication off how toxic this plant really is. Taste: The root is said to taste pleasantly like parsnip before poisoning the consumer. Hemlock Water Dropwort is in the Apiaceae family, one of great interest to foragers as the family contains many fine edibles and a good handful of deadly poisonous species.  

Medicinal Uses: Being the most poisonous plant in the UK, this is not used for medicinal purposes.

Common Name:   Rhododendron

Botanical Name:   Rhododendron Ponticum

Description:  Usually medium or large evergreen shrub that can become very large. Rhododendrons produce large bell-shaped flowers in clusters. The flowers come a range of colours spanning reds, yellows, pinks, purples and even white.

Height: Can get extremely large

Danger:  Poisonous

Areas affected:  Will grow almost anywhere. 

Main Causes Spreading: 

Invasive: Yes: As an introduced species. It is highly invasive. It destroys habitats and thus whole colonies of native plants and animals disappear.

Timing: Evergreen, Flowers in from May to August depending on where they are located.

Rhododendron 

(Pictured: Rhododendron Ponticum which is one of the most common varieties in the UK).

Rhododendron (from Ancient Greek: Rhódon "rose" and Déndron "tree") is a non-indigenous genus of various species of woody plants in the heath family (Ericaceae), either evergreen or deciduous, and found mainly in Asia, although it is also widespread throughout the highlands of the Appalachian Mountains of North America. It is also the national flower of Nepal as well as the state flower of West Virginia and Washington in United States, and state tree of Sikkim and Uttarakhand in India .

Rhododendron has become a very popular plant for people to have in their garden due to its evergreen nature and brightly coloured flowers that can bloom from late winter through to early summer. There are many different varieties of Rhododendron and a wide range of different coloured flowers (Reds, Pinks, Orange, Yellows, Purples, Blues, Cream, White etc) . There are hundreds of different varieties of Rhododendron and it would be impossible to cover all of them here.

A brief description of Rhododendron is a genus of shrubs varying from small to (rarely) large trees. The smallest species growing to 10–100 cm (4–40 in) tall, with the largest species Rhododendron Protistum var. giganteum, reported to grow to 30 m (100 ft) tall.

The leaves are spirally arranged; leaf size can range from 1–2 cm (0.4–0.8 in) to over 50 cm (20 in), exceptionally 100 cm (40 in) in Rhododendron Sinogrande. They may be either evergreen or deciduous. In some species, the undersides of the leaves are covered with scales (lepidote) or hairs (indumentum). Some of the best known species are noted for their many clusters of large flowers. There are alpine species with small flowers and small leaves, and tropical species such as section Vireya that often grow as epiphytes. Species in this genus may be part of the heath complex in oak-heath forests in eastern North America.

They have frequently been divided based on the presence or absence of scales on the abaxial (lower) leaf surface (lepidote or elepidote). These scales, unique to subgenus Rhododendron, are modified hairs consisting of a polygonal scale attached by a stalk.

Rhododendron are characterised by having inflorescences with scarious (dry) perulae, a chromosome number of x=13, fruit that has a septicidal capsule, an ovary that is superior (or nearly so), stamens that have no appendages, and agglutinate (clumped) pollen.

Both species and hybrid rhododendrons (including azaleas) are used extensively as ornamental plants in landscaping in many parts of the world, including both temperate and subtemperate regions. Many species and cultivars are grown commercially for the nursery trade.

Rhododendrons can be propagated by air layering or stem cuttings. They can self-propagate by sending up shoots from the roots. Sometimes an attached branch that has drooped to the ground will root in damp mulch, and the resulting rooted plant then can be cut off the parent rhododendron.

Many species of Rhododendrons are often valued in landscaping for their structure, size, flowers, and the fact that many of them are evergreen. Azaleas are frequently used around foundations and occasionally as hedges, and many larger-leafed rhododendrons lend themselves well to more informal plantings and woodland gardens, or as specimen plants. In some areas, larger rhododendrons can be pruned to encourage more tree-like form, with some species such as Rhododendron arboreum and Rhododendron Falconeri eventually growing to 10–15 m or more tall.

Rhododendrons flowering is a magnificent springtime spectacle – but they can be aggressively invasive to some of our finest and most precious countryside with catastrophic impacts on wild plants and animals.

One of the more common varieties Rhododendron Ponticum was first introduced to Britain, probably from Spain or Portugal. It was originally introduced by Conrad Loddiges as seed in 1763 to be used as a cultivated flowering plant in gardens, parks, and estates as a horticultural exhibit, but was also extensively planted in western Victorian hunting Estates under woodland canopies and on heathland areas to provide shelter for game species. They also used Rhododendron Ponticum as a rootstock for grafting scions from less hardy but more colourful stock from places such as China and the Himalayas.

But the shrub has often spread out of control with huge damage to many native woodlands, heaths and other wild places like the Snowdonia national park where they have spent millions trying to remove and eradicate it. It is estimated that the plant now covers 98,700 hectares, roughly 3.3 per cent of Britain’s total woodland, a report by the Forestry Commission found, and Scotland has been hit particularly hard, where it covers 53,000 hectares.

It has been determined through DNA analysis of naturalised ‘wild type’ Rhododendron ponticum, that most if not all of the invasive bushes in the British Isles originate from the Iberian Peninsula. A degree of backcrossing with the two species R. maximum and Rhododendron Catawbiense, proves that our invasive Rhododendron Ponticum plant in the British Isles is a hybrid species.

The main problem with Rhododendrons is that they grow into huge bushes with thick vegetation that blocks out sunlight and smothers most other wild plants and trees, stopping them from growing or regenerating. Its leaves are toxic to animals and repels wildlife from earthworms to birds. Many bushes have become infected with the highly pernicious tree disease called sudden oak death that threatens many types of trees and shrubs. Outbreaks of the disease in the UK, especially on larch trees, have often been linked to Rhododendron Ponticum.

The flowers of Rhododendron are very attractive to insects, particularly Bumble Bees. In the main flowering period of May/June, the exotic showy blooms monopolize the attentions of pollinating insects, virtually to the exclusion of all others. This means that the flowers of native plant species in the vicinity suffer from a lack of pollinating insects. As a result they may not successfully set seed. This is yet another way that Rhododendron may be detrimental to competing native vegetation.

All of this means that areas dominated by Rhododendron have an exceedingly impoverished fauna in comparison to native habitats, both in terms of species and of biomass. If there is little eating the Rhododendron, then it follows that there are few or no carnivores eating these herbivores and so also, few top carnivores. Song birds which feed on either seeds or invertebrates are reduced to trying to survive in smaller numbers by feeding in areas above or adjacent to the Rhododendron. Once the song bird populations decline so do species such as Sparrow Hawks which prey upon them.

Each plant can produce one million or more tiny seeds each year that spread in the wind, and it also spreads with massive tangles of branches rooting in the ground. The plant is incredibly difficult to get rid of by digging up or using herbicides. Snowdonia national park and several other sensitive areas have tried to destroy the invading rhododendron involving hundreds of people over many years digging up the plant. It’s expensive, time-consuming and takes years to completely eradicate.

Legislation:

Rhododendron Ponticum has now become classed as an invasive species of plant in the United Kingdom and Ireland. Rhododendron Ponticum is now covered by the Wildlife and Countryside Act 1981. It is listed under Schedule 9 of the Act and Section 14 of the Act states that it is an offence to plant or otherwise cause the species to grow in the wild.

Control Options:

Control of Rhododendron Ponticum as an invasive species in woodland is often the first operation in the restoration of native habitats. The choice of control or eradication method can influence the recovery of the site, and this should be considered when planning any control operations. The control options that can be undertaken include the complete or partial removal of Rhododendron Ponticum shoots before herbicide control will allow faster re-invasion of plants, especially if coupled with ground disturbance. The speed of recovery is also dependent on a local source of viable propagules.

Effect Control Measures:

The use of stem injection as a control method has been successfully trialled in Wales and Western Scotland.

The removal of the largest plants has until now posed the greatest challenge and expense to estate managers, their continued presence in the environment the greatest threat to the species’ long-term eradication, as mature bushes can produce up to a million seeds a season, continually re-invading surrounding habitats.

Injecting herbicide directly into the stems of large Rhododendron results in their death within six months. Not only is the dead material then easier to remove, but the application of the herbicide is more precisely targeted than in traditional methods, uses less product producing overall cost savings.

The National Trust for Scotland, Inverewe Gardens that are famous for their extensive Rhododendron collection, has recently been using the stem injection method to control seedlings from their hybrid Rhododendron Ponticum windbreaks invading surrounding woodlands.

Full Control Measures:

Current methods of management and disposal for Rhododendron Ponticum include the following:

Mechanical Control: Heavy digger machinery with long hydraulic arms are best for digging up the deep root material and crushing branches. However you do need to dig out all the root system to prevent re-growth. This is a very difficult operation because the roots will be very deep and can be wrapped around and under rocks. You will need to ensure that all root material is removed to prevent regrowth. (Good Operator knowledge of the machinery and habitat is key to ensure the heavy machinery does not compact valuable forest flora and fauna). Mechanical clearance must be followed by repeated herbicide applications for at least two years to prevent re-sprouting and recolonisation.

• Chemical Control: spray cut stems with chemicals, although surrounding vegetation may be affected by this.

• Disposal through production of biochar. This could be achieved by on-site charcoal production using modern portable reactors to reach optimum conditions. This can lead to a yield of 25-33% of the original material.

• Biological Control: There are few natural enemies associated with Rhododendron Ponticum even in its native range. Research is currently being undertaken into biological control, including the proposed use of a rust fungus from Portugal. This is currently being evaluated in other countries and is a possible cheaper, simpler alternative approach to chemical and mechanical control.

Once Rhododendron Ponticum has been removed from an area, a study by Maclean et al (2017) has shown that understorey plant community composition does not return to the state pre-invasion, even decades after the removal of Rhododendron Ponticum. The overall conclusion from the study states that native plant communities showed no signs of returning to pre-invasion conditions up to thirty years after the removal of Rhododendron Ponticum. It is suggested that restoration should focus on aiding the arrival of forbs and grasses under these circumstances, rather than altering the condition of the soil.

Toxicity of Rhododendron:

Potentially toxic chemicals, particularly 'free' Phenols, and Diterpenes, occur in significant quantities in the tissues of plants of Rhododendron species. Diterpenes, known as Grayanotoxin, occur in the leaves, flowers and nectar of Rhododendrons. These differ from species to species. Not all species produce them, although Rhododendron ponticum does.

These toxins make Rhododendron unpalatable to most herbivores. Phenols are most concentrated in the young tissues, such as young emergent leaves and buds. This provides a primary defense against herbivores, before the tissues have acquired the added deterrent of physical toughness found in older tissues. Young emergent leaf buds have the additional protection of a sticky exudate which also contains phenols. This physically discourages small invertebrates from eating the buds, because they get stuck in the exudate. Its poisonous nature must act as a further discouragement.

People have been known to become ill from eating honey made by bees feeding on rhododendron and azalea flowers. Xenophon described the odd behaviour of Greek soldiers after having consumed honey in a village surrounded by Rhododendron ponticum during the march of the Ten Thousand in 401 BC. Pompey's soldiers reportedly suffered lethal casualties following the consumption of honey made from Rhododendron deliberately left behind by Pontic forces in 67 BC during the Third Mithridatic War. Later, it was recognized that honey resulting from these plants has a slightly hallucinogenic and laxative effect.

Cases of human poisoning are also known. Most are caused by the consumption of honey produced from Rhododendron flowers. This is known as 'Mad Honey Disease', or 'Honey Intoxication'. Cases of this have been recorded from as far back as 400 BC. It results in relatively short-lived intestinal and cardiac problems and is rarely fatal. The severity of symptoms depends on the amount of contaminated honey consumed. It is worth thinking carefully about the siting of bee hives if Rhododendron is a prominent feature of the area.

The suspect Rhododendrons are Rhododendron Ponticum and Rhododendron Luteum (formerly Azalea pontica), both found in northern Asia Minor. Eleven similar cases have been documented in Istanbul, Turkey during the 1980s. Rhododendron is extremely toxic to horses, with some animals dying within a few hours of ingesting the plant, although most horses tend to avoid it if they have access to good forage. The effects of Rhododendron Ponticum was mentioned in the 2009 film Sherlock Holmes as a proposed way to arrange a fake execution. It was also mentioned in the third episode of Season 2 of BBC's Sherlock, speculated to have been a part of Sherlock's fake death scheme.

Grazing animals are discouraged from eating Rhododendron foliage because of its toughness and unpalatability. The unpalatability is learned and cases of poisoning may result in animals such as sheep and cattle if they ingest sufficient quantities because of extreme hunger or inexperience. The general toxicity of Rhododendron to herbivores means that it cannot generally be controlled by grazing.

In summary: Rhododendron is an introduced species. It is highly invasive. It destroys habitats and thus whole colonies of native plants and animals disappear. Because it is so expensive to control and physically prevents access, land has been abandoned. However such areas can be restored but reinfestation must be prevented.

Common Name:   Siberian iris or Siberian flag

Botanical Name:   Iris sibirica

Description:  It has long green grass-like leaves, a tall stem, 2–5 violet-blue, to blue, and occasionally white flowers.

Height: Can get extremely large

Danger:  Poisonous; Iris plants can cause digestive pain, nausea, vomiting, diarrhea, and fever if mistakenly ingested. Handling the plant may cause skin irritations or an allergic reaction.

Areas affected:  Will grow almost anywhere. 

Main Causes Spreading: N/A

Invasive: No

Timing: Flower in May to June

Siberian Iris 

The Iris sibirica (commonly known as Siberian iris or Siberian flag), is a species in the genus Iris. It is a rhizomatous herbaceous perennial, from Europe (France, Italy, Switzerland, Austria, Czech Republic, Slovakia, Germany, Hungary, Poland, Romania, Bulgaria, Former Yugoslavia, Belarus, Estonia, Latvia, Lithuania, Moldova, Ukraine, and northern Turkey) and Central Asia (including Armenia, Azerbaijan, and Siberia).   

It has long green grass-like leaves, a tall stem, 2–5 violet-blue, to blue, and occasionally white flowers. It is cultivated as an ornamental plant in temperate regions. It has creeping rhizome (approximately 0.9–1.2 cm (0.35–0.47 in) diameter), forming a dense clumping plant. The rhizomes are covered with the brown remnants of old leaves, from previous seasons.  The flowers come in a range of blue shades. From violet-blue to blue, and occasionally white. 

The flowers are 6–7 cm (2–3 in) in diameter.  It is known as iris de Sibérie (in French), sibirische Schwertlilie or Wiesen-Schwertlilie (in German) and strandiris (in Swedish).  

It has been around before the 1500s and was first called Iris augustifolia media by Carolus Clusius. Where it  is understood that it was first collected in Siberia by monks in the Middle Ages and grown in monasteries, later it was distributed around Europe, where there are now many cultivars. It has been cultivated in Britain since 1596  

Toxicity: Like many other irises, most parts of the plant, if not all of it is poisonous (rhizome and leaves), with the highest concentrations of toxins are found in the rhizomes (underground stems) and bulbs, while lesser amounts are found in the stems and flowers. Although there are few reports of humans ever dying, there have been a number of cases where livestock have died from ingesting the plant. They contain toxic compounds thought to be an irritant resin and a glycoside. Iris plants can cause digestive pain, nausea, vomiting, diarrhea, and fever if mistakenly ingested.   

Also handling the plant may cause skin irritations or an allergic reaction. The root has also been used to create an insecticide and an expectorant.  

Parents should keep an eye on curious small children and gardeners should know that sap can irritate the skin and even cause blistering in some people.