Widespread Panic - the jam scene’s middle child? (All photos by Kyle Gustafson/FTWP)

So what does that make Widespread Panic?

The Athens, Georgia-based sextet is the jam scene’s middle child. Amongst the big names - The Grateful Dead, Phish, Dave Matthews Band - they’re often forgotten. But they’re pros none the less, a long-running band that faithfully adheres to the genre’s core conceits.

That is to say, they can wail for a long time.

Tuesday night the band - which is currently celebrating its 25th year on the road - landed at Warner Theater, performing the first concert of a two-night stand. Spanning two sets and three hours, the show was heavy with brow-crinkling guitar solos, wiggly grooves, and spaced-out asides.

As bus-hippie bands go, Widespread Panic are traditionalists - riding the gritty Southern rock riffage of The Allman Brothers Band and Little Feat well past the 10-minute mark.

During the first set, the band reached deep into its back catalog for HORDE-festival-era fare like “Space Wrangler” and “Ain’t Life Grand.” They honored their forebears with a funked-up cover of the Grateful Dead’s “New Speedway Boogie.” The concert’s second half skewed a little loopier with drum-circle space-outs and extended improvisations.

By hour three, the audience had set inhibitions aside - aging longhairs suffered ecstatic, jelly-legged, melt-downs and young, hemp-necklace-clad, Garcia acolytes twirled through the back rows. A few people crouched behind their seats to sneak covert tokes of weed.

But not all jams are created equal. During the second set, the band’s energy dipped a little low. It was reflected in the crowd. The guy in the ironic “Betty Ford Clinic” ball cap, who was previously deeply engaged, stepped out for a refill. But within 10 minutes, another middle-aged fellow, sitting in the balcony, started miming Jimi Hendrix’s flaming guitar-pose.