However, spinach and other dark leafy greens contain higher amounts of oxalic acid which is known to cause kidney stones or kidney damage if you take in too much for too long. (truthaboutabs.com)
Since the leaves of rhubarb have the highest content of oxalic acid, only the stalks are eatable. (all-about-food.org)
Feeding foods either low in calcium, high in phosphorus or high in oxalic acid causes calcium to be leached from the iguana's bones in order to maintain organ function. (svg-vets.com)