The dangerous plants lurking in plain sight

On Monday, it emerged children's lives were "at stake" in a Suffolk village after hemlock - a plant that can be fatal if ingested - was found along their normal walk into school. Hemlock, however, is far from our only green neighbour that poses a risk.

First reported to Suffolk County Council in June by parish council chairman David Brinkley, the authority has pledged to close the road and remove the offending plant.

In his call to action, Mr Brinkley says delays to the plant's removal "put children's lives at stake".

Head teacher Rachael Rudge has similar concerns.

"To walk on the roads because the path isn't safe because of all the hemlock and vegetation overgrowing, they're being put in this really difficult and unsafe position," she says.

But according to Prof Iain Barr, of the University of East Anglia, the removal of the hemlock leaves a further 28,000 still dotted around the UK.

Prof Barr, a professor of field ecology, tells the BBC about a number of other dangerous plants sitting in plain sight and why some pose such a threat.

The giant hogweed - Heracleum mantegazzianum - is not to be messed with, says Prof Barr.

"If you touch it and your body reacts to it, it can cause a reaction and makes you very susceptible to sunburn," Prof Barr says. "You don't want to come into contact with any part of it."

The toxic sap of the plant, which grows near canals and rivers, can cause burns, blisters and scarring to those who touch it.

The plant, a close relative of cow parsley, has white flowers, thick bristly stems and can grow more than 16ft (5m) tall.

Native to Central Asia, it was introduced into Britain in 1893 as an ornamental plant, but "escaped from domestication".

Toxic components in the leaves, stems, roots, flowers and seeds can be transferred to skin by touch.

It is often confused with its native relative, the common hogweed.

"That's also toxic," says Prof Barr. "But less so."

A staple favourite for a shadier spot in the garden, the much-loved foxglove's floral beauty comes with a dark side.

Foxglove - digitalis - is a source of digitoxin, a glycoside in the drug digitalis, which has been used as a heart stimulant since 1785.

It is also well-known for its toxicity in all parts of the plant.

Consuming the leaves can cause oral and abdominal pain, nausea, vomiting and diarrhoea.

In severe cases, symptoms can include visual disturbances, plus heart and kidney problems.

"People should just stand back and admire it," says Prof Barr.

"Don't eat it," says Prof Barr.

Deadly nightshade is one of the UK's most poisonous plants and just a couple of berries, which contain tropane alkaloids, would be enough to kill a person.

"It is part of the tomato family," says Prof Barr. "It can be found in woodlands, though it is not quite as common as it used to be."

Despite its deadly potential, the nerve-gas antidote atropine sulphate can be extracted from it.

"The hemlock water dropwort is very, very common around the [Norfolk and Suffolk] Broads," says Prof Barr. "It is also very toxic."

Also known as the "poison parsnip", hemlock water dropwort - Oenanthe crocata - is one of the most poisonous plants native to the UK.

Both hemlock and hemlock water dropwort are part of the carrot family, but live in different habitats and have different toxins.

Hemlock on the other hand contains five alkaloids - coniine, conhydrine, pseudoconhydrine, methyl-coniine and ethyl-piperidine - which cause violent vomiting and paralysis of the nervous system.

But how do plants become so toxic that they can kill people?

"It is all to do with chemistry and evolution," says Dr Barr. "Plants have developed toxins to avoid being eaten.

"So a plant that is slightly more toxic to a grazing animal than the ones next to it has a slight advantage.

"Over time, this process leads to a point where certain plants can become very toxic to certain species."

The majority of the UK's native toxic plants evolved their toxins to deter huge creatures like woolly mammoths or 2m (6ft 6in) tall aurochs, rather than us humans, he said.

"If an auroch or mammoth overgrazed, then the plant alkaloids would make it not feel very well," he says.

"It was not designed to kill them, just to make them unwell and to stop eating."

Plant toxins certainly did not develop, he says, to prevent children from walking to school.