Not long ago I stumbled across an article which estimated that a 130-pound woman would need to consume something like ten pounds of rhubarb leaves in order for toxicity to build up to a level where it would be lethal. Now that's a lot of leafy greens. I think my jaw would give out long before I was able to chew through one pound, let alone ten.

But this got me wondering what it is about rhubarb leaves that makes them inedible. So I hit the books. That mystery substance is called oxalic acid and when ingested it can bind to several key nutrients including calcium, iron, sodium, magnesium and/or potassium, interfering with the body's ability to absorb them properly. Although my potential plant-licking six-year-old self was once convinced I would die if my tongue misbehaved within close proximity to the rhubarb plant, the more likely outcome would have been abdominal pain, nausea, vomiting, diarrhea, weakness, drowsiness, breathing difficulties or convulsions (not to mention a mildly ticked off mother).

Rhubarb leaves are not the only place where oxalic acid is found. It's also present in chocolate, coffee, strawberries, cranberries, most nuts, beans, beets, bell peppers, parsley, peas, potatoes, spinach, Swiss chard, summer squash, sweet potatoes, tea - and the list goes on. Rhubarb stems also contain measurable amounts, but it’s the excessive level in the leaves which formed the basis for my mother's warning.