Somewhere in the middle of a lengthy tour, Decemberists guitarist Chris Funk and bassist Nate Query had an idea: why not start an all-acoustic, all-instrumental band specializing in the weirder side of bluegrass?

“We just decided that would be a fun thing to do,” Query explains, in a telephone interview from his Portland, Oregon, home. But as often happens, that fun thing has gotten a little out of hand. With drummer John Moen the latest to join the fold, what started as a hotel-room duo has now become a full-fledged sextet. And with Decemberists frontman Colin Meloy taking time out to pursue literary ventures, Black Prairie has at least temporarily become the main musical outlet for four-fifths of his band. Keyboardist Jenny Conlee is the other Decemberist in the group, which also includes singer-violinist Annalisa Tornfelt and guitarist John Neufeld.

“The idea originally was to be totally acoustic, totally instrumental, and totally collaborative,” Query notes. “So we’ve maintained the acoustic and we’ve maintained the collaborative, but once we heard Annalisa sing we couldn’t help ourselves, and we’ve moved a little bit more in that direction. Especially now that we’ve added drums.”

The band has definitely branched out from its bluegrass beginnings. Although Black Prairie records for the Nashville-based Sugar Hill imprint, its music has more to do with the Old Country than New Country. Mournful Eastern European folk stylings inflect several tunes on the band’s 2012 release A Tear in the Eye Is a Wound in the Heart, while “Dirty River Stomp” is an accordion-led ragtime ramble and “34 Wishes: The Legend Of” is an eerie venture into acoustic prog-rock.

Americana isn’t entirely ignored, however. “For the Love of John Hartford” is an affectionate nod in the direction of the late, great Nashville eccentric, while the Tornfelt-sung “Richard Manuel” honours the Ontario-born Band vocalist’s wayward spirit. That the latter makes ghoulish reference to Manuel’s suicide suggests Black Prairie shares more than four musicians with the often-morbid Decemberists.

“Well, some of the other band names we came up with were, like, Death on the Prairie and Black Prairie Death and stuff like that,” Query quips, before adding that he and his fellow musicians are more excited about moving forward than settling in for the big sleep. “As individuals, all of us are very much restless and looking for new challenges,” he says, and Black Prairie surely fits that bill.