plants include fat hen ("lamb's quarters"), sorrel, and several Oxalis species. The root and/or leaves of rhubarb and buckwheat are high in oxalic acid. Other edible plants with significant concentrations of oxalate include, in decreasing order, star fruit (carambola), black pepper, parsley, poppy seed, amaranth, chard, beets, cocoa, chocolate, most nuts, most berries, fishtail palms, New Zealand spinach (Tetragonia tetragonioides), and beans. Leaves of the tea plant (Camellia sinensis) contain among the greatest measured concentrations of oxalic acid relative to other plants. However, the drink derived by infusion in hot water typically contains only low to moderate amounts of oxalic acid due to the small mass of leaves used for brewing. Physiological effects Excess consumption has been linked to gout and kidney stones. Many metal ions form insoluble precipitates with oxalate, a prominent example being calcium oxalate, the primary constituent of the most common kind of kidney stones. The highly insoluble iron(II) oxalate appears to play a major role in gout, in the nucleation and growth of the otherwise extremely soluble sodium urate. This explains why gout usually appears after age 40, when ferritin levels in blood exceed 1 μg/L . Foods high in oxalate are often avoided by people at risk of gout. In studies with rats, calcium supplements given along with foods high in oxalic acid can cause calcium oxalate to precipitate in the gut and reduce the levels of oxalate absorbed by the body (by 97% in some cases). Some fungi of the genus Aspergillus produce oxalic acid. As a ligand for metal ions Oxalate also forms coordination compounds where it is sometimes abbreviated as ox. It is commonly encountered as a bidentate ligand. When the oxalate chelates to a single metal center, it always adopts the planar conformation. As a bidentate ligand, it forms a 5-membered MC2O2 ring. An illustrative complex is potassium ferrioxalate, K3[Fe(C2O4)3]. The drug oxaliplatin exhibits improved water solubility relative to older platinum-based drugs, avoiding the dose-limiting side-effect of nephrotoxicity. Oxalic acid and oxalates can be oxidized by permanganate in an autocatalytic reaction. One of the main applications of oxalic acid is rust-removal, which arises because oxalate forms water-soluble derivatives with the ferric ion. Excess An excess oxalate level in the blood is termed hyperoxalemia, and high levels of oxalate in the urine is termed hyperoxaluria. Acquired Although unusual, consumption of oxalates (for example, the grazing of animals on oxalate-containing plants such as