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Monique Keiran: Poison hemlock moves in uninvited

Our benign climate welcomes yet another uninvited transplant to the region. Poison hemlock joins hundreds of other invasive plant species that make themselves at home here. Like some of those other plants, it contains toxins.

Our benign climate welcomes yet another uninvited transplant to the region. Poison hemlock joins hundreds of other invasive plant species that make themselves at home here.

Like some of those other plants, it contains toxins. Unlike most of them, it resembles a common cooking herb, and can be easily mistaken and eaten as such.

Native to Europe, poison hemlock gained lasting notoriety 2,400 or so years ago as the poison used to kill Greek philosopher Socrates. In 2002, two people went into respiratory arrest and were hospitalized after eating parts of the plant.

Poison hemlock must be handled with care and gloves.

Consider it part of the evolutionary arms race between plants and animals.

Plants, after all, have little control over where their seeds land and sprout. They grow and send out all kinds of green bits to make food, which is necessary to fuel reproduction and the continuation of the species.

Yet, after all that effort, some herbivore with two, four, six or even no legs can just come along and eat all of the plants’ soft, tender bits. It’s like investing in a pension plan for decades, then having the company renege on the contract just as you approach retirement. Or dutifully putting a percentage of your income into savings every month, then having the government seize all bank assets.

And being plants means being planted. Plants can’t just get out of the way. They can’t pick up their sticks and move to a friendlier neighbourhood.

Longer-term, incremental solutions emerged. Over the course of millions of years, plants did take matters into their own, er, needles and leaves, and Nature continued the Wild West between eaters and their prey.

Over generations, some plant species developed thorns, spines and prickles. That deters some plant-munching animals, but not all. Victoria’s own Columbia black-tailed deer, for instance, adeptly strip flowers and leaves off even the super-prickly Harrison yellow roses in my garden.

Some plant species invested in hard, woody structures and tough leaves. That dissuades some herbivores, but not all. Deer persist in pruning my bay laurel bush to a stump, even though they then spit out the twigs and leaves.

Some plant species adopted the Borgia Method to deal with enemies. Some infused their leafy bits with poison. Some focused on protecting only their seeds by encasing them in poisonous husks or adding poison to the seeds themselves.

And some plants — like poison hemlock — became toxic through and through.

Many of the poisons are alkaloids, chemicals that can cause any number of reactions in unwary herbivores. Reactions can include bloating, uncontrollable peeing, diarrhea, lesions, welts and rashes, loss of co-ordination, muscle twitching and spasms, joint dislocation, nervousness, salivation, teeth grinding, trembling, internal bleeding, vomiting, jaundice and kidney failure, hallucination, respiratory failure and asphyxiation, convulsions, coma and death. Depression is also possible, which is hardly surprising given that list.

The toxin strategy also sort of works, depending on the plant, the animal, the poison and whether an ancient Greek ruling class or a member of a particular 15th-century Roman family administered it.

In some plants, the poisons not only helped deter herbivores but suppressed other nearby plant species so that the poisoner had more sun, water, soil nutrients and space in which to grow. Broom and Daphne laureola both do this.

Animals fought back, of course. Some species developed ways to neutralize the poisons before they can take effect. Some developed tolerances for some poisons. Birds can eat many berries and nuts that would make humans ill, such as rowan, Daphne laureola and horse chestnut, for example.

Some animals developed a liking for some of the poisons. Some humans seek regular fixes of plant alkaloids caffeine, nicotine, cocaine and theobromine (chocolate’s feel-good chemical).

We use other plant alkaloids in small, controlled doses for medication, for example, codeine, morphine, quinine and reserpine.

As for poison hemlock, no mammal species has yet evolved a way to easily withstand its toxins. So watch for it. If you find a parsley-like plant with purple splotches on its stems, wear gloves and long sleeves to remove it.

And don’t eat it.

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