@stuartk: Rodney Crowell first became a National name as the leader of Emmylou Harris’ Hot Band. He played acoustic rhythm guitar and sang harmony with her, and her band included the likes of Tony Brown (later becoming a major Country music producer), Albert Lee (everyone’s favorite Tele player), Emory Gordy, Jr. (later in Dylan’s band), guitarist/mandolinist/singer Ricky Skaggs, and pedal steel master Hank DeVito (and writer of "Playing With The Queen Of Hearts", the best version being that of Dave Edmunds). Buddy Miller now serves Emmylou Harris as her bandleader.
It is my opinion that to qualify as Americana, the music has to have the "Southern" feel, as does Country. I don’t know how to characterize "Southern", but I know it when I hear it, and know when I don’t. It is conspicuously absent in the music of many of the Alt-Country artists and bands. To hear it, listen to the music containing the playing of The Swampers, the renown Muscle Shoals studio band.
There is a good book entitled Country Music: White Man’s Blues, written by John Grissim and published in paperbook in 1970. Highly recommended.
John Hiatt is almost a genre unto himself (as is Dylan, Richard Thompson, Van Morrison, and other unique and unclassifiable artists). John Hiatt’s Bring The family was for years my favorite album, and is music making at the highest level. Hiatt isn’t Country, being more of a Blue-Eyed Soul singer and writer. But remember, in the 1950’s Blues was considered a form of Folk music. In the South, all musical forms tend to get integrated. Elvis’ five Sun singles (and 78’s) contained a Blues on one side, a Hillbilly on the other. Hank Williams learned to play guitar from a local Blues street musician.