Despite all these things warnings, plants containing oxalic acid are still edible. Oxalates probably inhibit the absorption of calcium found in the same food, but not in other foods eaten at the same time. Cooking will decrease the amount of oxalates in a food (it goes into the cooking water). Some plants that are probably somewhat high in oxalic acid are amaranth, chives, lambsquarters, parsley, purslane, rhubarb and spinach, and possibly beet greens and swiss chard.
So what about rhubarb leaves, which contain high oxalic acid, and have caused reported deaths when eaten, even cooked? They apparently also contain anthraquinone glycosides, which alone, or together with the oxalates, are what likely causes the poisoning. So go ahead and eat plants containing oxalic acid, but if you worry about these things, don't eat five pounds, raw, in a single sitting.