There's a lot of cross-over and sometime the reverse is true- See: Thread on "Such A Getting Upstairs" (an American minstrel tune that became a Morris Dance tune!) There are some major song branches that have crossed over:

Acres of Clams/Rosin the Beau/Bow/Lay of the Old Settler;

Awake Awake/In Old Virginnny/East Virginia/ Drowsy Sleeper/Katie Dear/Silver Dagger;

Bonaparte's Retreat Group;

Bunclody/Cuckoo/Love's Farewell;

Cuckoo's Nest;

Devilish Mary;

This is just up to the letter D in my "Fiddle Tune" category. I'd say there are thousands of cross-over tunes. Where do we go from here?

-Richie