I find it ironic - okay, I find it slightly hilarious - that the house plant which results in the most calls to poison control centers is called the Peace Lily.

Next on the list is Pokeweed - which people have a bad habit of mistaking for other edible wild plants - followed by two holiday favorites, poinsettias and holly plants.

As the Peace Lily is popular at Easter, one could conclude that holiday plants are particularly dangerous. But there's actually a more interesting - if less amusing - background to such risks.

Most of the calls, of course, aren't funny at all. They concern curious children and pets who've been somehow tempted by an attractive plant that sits within easy reach. I imagine that the resulting emergencyÂ calls are fast and panicked as one of the major symptoms of eating peace lilies is a fierce burn in the mouth.

It's not actually that peace lilies are so uniquely poisonous. The compound that makes them dangerous occurs in many plants. It's more that we bring them into our homes - for both their beauty and their symbolism - without really knowing anything about the chemistry that flourishes within.

Peace lilies contain an usually high concentration of oxalates, which are are tidy little structures of carbon and oxygen with an unusual affinity for calcium. Many edible plants contain oxalates including spinach, parsley, beets, rhubarb, and buckwheat. Nutritionists, in fact, usually take care to point out that while leafy green spinach is naturally high in calcium, it also absorbs calcium out of the blood stream, somewhat neutralizing the benefit.

Which brings us back to the calcium-spongeÂ qualities of peace lilies and other houseplants high in oxalates, including Calla lilies, Diffenbachia, and Philodendron. Here is another example of the dose making the poison. The compound binds rapidly with calcium in the bloodstream, forming calcium oxalate crystals. As calcium levels in the body drop precipitously, a chain of toxic effects occurs.

First the tissues of the mouth, tongue and throat burn and swell. Then acute nausea follows. In high enough doses,Â continued depletion of calcium disrupts cell membrane function, causing tremors and a sudden lethargy. The crystals themselves can become lodged in the kidneys and do serious harm there.

The 2007 Annual Report of the American Association of Poison Control Centers documents 7638 calls concerning plant oxalate poisoning. Most of these (6020) were children under six and another 762 involved children from 6-19. You'll be glad to know that no one died. But more than a thousand ended up in a doctor's care and several were sick enough to be hospitalized.

Knowing the chemistry, you'll appreciate that for minor exposures, experts often recommend flushing the mouth out with water and then - once nausea passes - forcing foods with a high calcium content such as milk and yogurt to counteract the calcium depletion. Check with your doctor or poison control center first, of course.

But we can all agree that this would be a good time to pass on the spinach.