There are none.

The bulbous root is the only commodity for which futures trading is

banned. Back in 1958, onion growers convinced themselves that futures

traders (and not the new farms sprouting up in Wisconsin) were

responsible for falling onion prices, so they lobbied an up-and-coming

Michigan Congressman named Gerald Ford to push through a law banning

all futures trading in onions. The law still stands. And yet

even with no traders to blame, the volatility in onion prices makes the

swings in oil and corn look tame, reinforcing academics’ belief that

futures trading diminishes extreme price swings.

Amazing, onion farmers and Congress panic in 1958 with the Senate Committee arguing that

…speculative activity in the futures markets causes such severe and unwarranted fluctuations in the price of cash onions…[that a] complete prohibition of onion futures trading [is necessary] in order to assure the orderly flow of onions in interstate commerce…

and for going on fifty years onion futures are banned. Makes me want to cry.

More here on the banning of futures markets . (A report from 1956 indicates that the fluctuations at that time were due to an attempted swindle.)

Hat tip to Newmark’s Door