It’s a big country, this America, and Americana music is concomitantly enriched by its host nation’s geography and diversity. That was on display Wednesday night as Roots hosted artists from New York, Texas, Massachusetts and Washington. Strings were stretched, along with rules and genre boundaries. There’s no point in reaching for a fancy way to say it. This one was a delight and the crowd seemed to agree, what with all the frequent standing and applauding.