> Oxalic acid occurs in many plants and is toxic in very large amounts. Some
> of the plants that contain a significant amount of oxalic acid are
spinach,
> collards, and rhubarb. Because oxalic acid binds with calcium and iron, it
> inhibits their absorption by the body and is not well-assimilated.
>
> If a person is having difficulty with his, symptoms can occur like kidney
> stones and vulvar pain  in women.

Here are a couple of links to info you might find useful:

http://www.branwen.com/rowan/oxalate.htm

http://www.ixion-biotech.com/home.htm

Norm