Well, Lox, I'd call it G. Which has a D chord in when you need it. As it happens, if I am going to play that song, I use a D/A diad not a D chord.

There do however seem to be some oddities about what fits to "Famous flower of serving men". If I play that where I usually do (the strings being GDGBCD - it's done with two capos) the melody falls all on white notes but a Gm chord can be played (on a guitar in standard tuning) pretty well throughout the song if I don't play the guitar part but leave it to the fiddle to play the tune.