One night, when a band didn’t show up to play its gig at Toad, singer-songwriter Ry Cavanaugh took matters into his own hands. Cavanaugh grabbed a couple mics, duct-taped them to a table, and gathered some pals to jam on an improvised setlist.

“It was sort of a magical moment that transformed the bar into this intimate listening space,” drummer Billy Beard told the Herald.

Two decades on, the club — Cambridge institution Toad — has closed. But the band born that night, way back in the fall of 2003, is still going strong.

Beard says Session Americana “began as a lark.” The core of the band (both back then and now), Beard, Cavanaugh, Dinty Child, and Jim Fitting already had plenty of musical outlets so Session Americana would be a loose side gig, a fun diversion that wouldn’t distract anyone from more serious projects.

Session Americana is still loose and still fun. But against all odds, it’s become a defining Cambridge act and legendary out-of-town success. The folk/rock/country/blues/kitchen sink collective has made ten albums (the 11th is in the can and coming soon). It has logged as many international tours — after four shows at Passim later this week, the group will spend a month in Europe.

“The surprising part of it has been the popularity piece,” Beard said. “We started to sell out venues, then play bigger ones, then tour internationally.”

Maybe the popularity has shocked Beard, but the magical chemistry and diversity of Session Americana deserves every ounce of love it’s received. Despite the long history, the group remains fresh by swapping in and out members and ace guests like current participant Eleanor Buckland. The improvised nature has never been lost even while the songwriters have round out the catalog with haunting, hollering, heartbreaking originals.

“In those early days at Toad we did do a lot of covers, and those covers fell away as we started to write more seriously for the band,” Beard said. “It can be challenging to have these disparate voices all writing and still make the songs our own. But it seems to have worked.”

Session Americana no longer huddles around a single table. As the venues became larger, that set up just didn’t make sense. But Beard makes it clear that the free-wheeling hootenanny spirit is very much alive and well.

“(There’s) still a lot of instrument swapping, group harmonies and projecting an overall sound from the stage,” he said. “What we were doing when we started was really unique at the time. There wasn’t really anybody doing what we were doing in 2003, 2004, 2005. And it was just so much fun. We did it for the sheer joy of it.”

That joy still permeates the group.

“It’s kind of funny, every year there is one day where we get together and go, ‘Do we want to keep doing this?,’” Beard said. “And everyone is like, ‘Yeah, great, I’m all in.’”

For tickets and details, visit sessionamericana.com