The giant hogweed is big, sculptural and highly toxic. Its sap can cause skin blistering and blindness. (iStock)

Plants cannot run from existential threats. They have to sit there silently and take a licking.

But they’re not stupid. Many grow armor of sorts — though how deer can devour rose thorns without leaving a trail of blood has always puzzled me. More insidiously, some plants produce chemicals that either assault your skin or make you sick if you eat them.

As a result, many pose risks to those who stumble across them, whether in the garden, the city park or some of the beautiful mountain trails that lace the central Virginia Piedmont.

This is the domain of Alfred Goossens, a retired flavor chemist whose Madison County home has a view of the Blue Ridge Mountains. He is close to Old Rag, a favorite hiking mountain for folks across the region.

But you don’t have to go on a three-hour country walk to find plants that want to bite you. The other day, I joined Goossens and Don Hearl, both Virginia Master Naturalists, in a stroll of Goossens’s own 14-acre property.

Along a tree line just a few steps from the front door, they pointed out a suite of potentially harmful plants, namely horse nettle (poisonous fruit), Virginia creeper (skin irritant), poison ivy (enough said) and pokeweed (toxic from head to toe).

“If you took people outside like this, they wouldn’t know what was poisonous or nonpoisonous,” Hearl said. “They would just refer to them as weeds.”

Anyone who has spent time in the garden has probably had a run-in with poison ivy. Even savvy gardeners can miss seedlings that sprout amid other vegetation. Other toxic plants are not as common or as firm in the mind’s eye, but still can cause real problems.

Earlier this year, Goossens and other members of the naturalists’ Old Rag Chapter identified a tuber that a resident had dug up and eaten, thinking it was a sweet potato. It was actually the large fleshy taproot of the pokeweed, which is highly toxic and put the man in intensive care and close to death before the naturalists (and his doctors) came to the rescue.

I’ve long considered the fact that although the garden is full of potentially lethal vegetation, including daffodil bulbs and colchicums, this doesn’t play out in mass poisonings. You don’t see yards littered with corpses. But maybe I’ve been too complacent.

Christopher Holstege, medical director of the Blue Ridge Poison Center, tells me that the center received 7,182 calls between 2007 and 2017 pertaining to plant exposures. Most are handled over the phone, some callers need immediate medical attention, and some require lifesaving intensive care. He recounted the case of a ­26-year-old man who had gone foraging for ramps, the wild leek delicacy, and picked and ate the foliage of the false hellebore instead. The leaves are similar — broad with long folds — but false hellebore (Veratrum viride) is decidedly not for eating. (Nor is it related to the popular garden hellebore or Lenten rose.) After just four bites, the patient became ill — in the hospital his vital signs showed a heart rate of 42 beats per minute (bpm). You don’t need to be a medical pro to know that’s alarmingly sluggish. Thankfully, he recovered.

(Many seemingly innocuous garden plants are also toxic to pets. Lists of potential problem plants for dogs and cats have been compiled by the American Society for the Prevention of Cruelty to Animals.)

Goossens said it’s a safe bet that for all the thousands who contacted the poison center in Charlottesville — it covers the entire western half of Virginia — there were many more whose encounters with toxic plants go unreported.

In March, Goossens’s group and the Virginia Cooperative Extension education service released a downloadable publication called “The Socrates Project: Poisonous Plants in Virginia.” It lists and describes 11 plant species you want to avoid, and its title is inspired by the Greek philosopher who was sentenced to kill himself by drinking a potion of poison hemlock.

Here are five plants you should give a wide berth (including poison hemlock):

Pokeweed (Phytolacca americana)

Pokeweed is everywhere, in both town and country, because the seeds in its distinctive clusters of black berries are planted by birds. As a perennial, it gets larger each year and can attain the size of a large shrub by late summer. The stems are thick, upright and branched, and have a pinkish-red cast to them. Avoid skin contact with the plant and keep children away from the berries, which are not unlike blueberries. Pokeweed is one of the most common sources of plant poisoning in the United States. It is also known as “poke salad,” because in the South it has been traditionally used as an edible green, but only the young spring growth and only after it has been boiled twice. These culinary nuances are being lost in the 21st century, according to Hearl, who grew up in southwestern Virginia. Grow some lettuce or kale, and leave the pokeweed alone.

As for the berries, Hearl was warned against eating them “at a very young age, and I have started to do the same thing with my own grandchildren.”

Poison ivy (Toxicodendron radicans)

As they say, “Leaves of three, let it be.” The plant forms thick, hairy roots in old vines that climb trees, but younger forms may resemble shrubs. Even when young, every part of poison ivy contains a blistering agent named urushiol. If you live in a locale where you can burn yard waste, be careful not to have poison ivy as part of the mix, because the oil is released into the smoke and settles on the skin. Inhalation is particularly dangerous, and Holstege said he has had to treat firefighters afflicted during prescribed burns.

According to the book “Weeds of the Northeast,” at least 6 out of every 10 people get dermatitis from poison ivy. One fairly common source of contact is through your dogs and cats. They roll around in the vegetation, get the oil on their coats and then come indoors and invite petting.

Jimson weed (Datura stramonium)

The common name is a corruption of Jamestown weed, but it is the botanic name that gives a better clue to its hazards. Jimson weed is related to the daturas and brugmansias of the Americas, long used in shaman rituals to induce hallucinations. These plants are highly toxic and potentially lethal if the leaves or seeds are ingested or made into a tea. Who would purposefully take this poison? “Primarily adolescents,” Holstege said. Kids in search of a high are usually soon seeking an emergency room instead.

Poison hemlock (Conium maculatum)

It is hard to grasp that the carrot family would include some of the most malevolent plants on earth, including poison hemlock. Its toxin, coniine, causes muscle paralysis and death.

A herbaceous biennial once confined to the Old World, poison hemlock is now at large in Virginia and across the United States. It has the characteristic lacy leaves and white flower umbels of its clan, which also includes Queen Anne’s lace. It is not to be confused with the native conifer named hemlock.

Why would anybody mess with poison hemlock? By mistake. Its root resembles the edible root of the wild parsnip, its leaves look like parsley, and its seeds suggest aniseed. Its hollow stems have been made into toy whistles with tragic results.

Giant hogweed (Heracleum mantegazzianum)

Reports of giant hogweed’s spread to the Mid-Atlantic have induced a fair amount of dread. This is another summer-flowering carrot relative, but it can grow to 10 feet or more in its second or third year. It is perhaps in its juvenile stage, when it is smaller, that it poses a greater risk through mistaken identity.

The sap contains a blistering agent named furocoumarin; don’t touch any part of this plant.

“There is no worse plant than giant hogweed,” said Goossens, who grew up in the Netherlands, where it’s a fairly common weed. “The blisters are horrible, very, very painful,” he said. “If you get the sap in our eyes, the chance of getting permanent blindness is significant.”

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