My eye happened to fall on the entry couch grass in Merriam-Webster and the first definition was quack grass. I found that amusing; then I noticed the etymology said "alteration of quitch." Intrigued, I went to the American Heritage and found that they actually had an entry for quitch grass, whose etymology read "[Middle English quich, from Old English cwice; see gwei- in Indo-European roots]." (The PIE root gwei- means 'to live' and gives us the native quick as well as the borrowed Latin viv- and Greek bio- and zo(o)- words.) And it said couch grass was "Also called quack grass, witch grass." I found that an interesting cluster of forms, and I thought I'd pass it along.
Today, by the way, is [a month from] Jelly Roll Morton's birthday. He may not have invented jazz, as he used to claim, but he sure helped get it off on the right track. Happy birthday, Doctor Jazz! [Oops: I took the birthday info from another site without checking; it's actually Oct. 20, as a commenter points out. Let this be a lesson to me. Oh well, any day is a good day to listen to Jelly Roll!]