Even when the Roots are alone on the bill, there are a whole bunch of bands on stage.

This Philadelphia collective's picnic basket overflows with musical goodies. Look inside, and you'll find a full-on soul revue and an old-school rap outfit. There's a furiously shredding noise-rock band, and a tasty improvisational jazz ensemble. Not to mention an astonishingly focused hip-hop wrecking crew - leaders in bringing a genre-blending vision to life on stage.

So the Roots Picnic, offered over 10 sweltering hours Saturday at the Festival Pier, was an idea whose time has come.

The Roots - like that guy Walt Whitman - contain multitudes, and they were joined by a multitude of acts, including pop eccentrics Gnarls Barkley, soul revivalists Sharon Jones & the Dap-Kings, and experimental rockers Deerhoof.

The Roots - fronted by rapper Tariq "Black Thought" Trotter and anchored by drummer Ahmir "?uestlove" Thompson, who served as host and tossed out bottles of Vitaminwater and toyed with his cell phone while keeping the beat - opened things with a surprise mini-set.

The first non-Root to perform was Esperanza Spalding, 23, a jazz bassist and youngest instructor ever at Boston's Berklee College of Music. Her songwriting needs seasoning and her stage patter was pedantic, but she's a talent who delivered a welcome midafternoon breeze.

J*Davey, the Los Angeles duo of singer Briana Cartwright and keyboard player Brook D'Leau offered crisp, catchy songs served up 1980s New Wave with a funk twist. ?uestlove played drums, and they covered the Police's "Message in a Bottle."

Then came, Part II of the Roots, in "Go Get a Late Pass" power trio mode, with Thompson, guitarist Kirk Douglas, and sousaphone player Damon "Tuba Gooding Jr." Bryson. Thompson told the interracial crowd, whose favored fashion statements were Barack the Vote shirts, that "if John McCain is elected, we'll have to sing this song for the next 100 years."

They launched into Bob Dylan's "Masters of War," reimagined as a stately art song-turned-Hendrix-style guitar onslaught. Then the rest of the band came on, augmented by DJ Jazzy Jeff, and became a horn-happy R&B and funk outfit.

The next three acts excelled in divergent ways. Chicago duo the Cool Kids were clever and concise, fresh and clean. Deerhoof, from San Francisco, was the most out-there, with Satomi Matsuzaki fronting a shrewd garage band. And Brooklyn's Dap-Kings revitalized Stax-Volt '60s soul truisms with full-throated passion.

The Roots' marquee set offered wonders too vast to thoroughly explore here. It was a stunning showcase for Black Thought, who demonstrated seemingly impossible feats of breath control in taut salvos such as "Long Time" and the Sly Stone-sampling "Star."

It highlighted Douglas, as a guitarist and singer, who scatted as "You Got Me" morphed into Stevie Wonder's "Don't You Worry About a Thing" and then Rodgers and Hammerstein's "My Favorite Things." It was an exhaustive, and exhausting, performance by one of the greatest of live bands.

And it made it mighty tough on Gnarls Barkley, the closing duo of singer-rapper Cee-Lo Green and producer-keyboard player Brian "Danger Mouse" Burton. The pair struggled to elicit enthusiasm - though things perked up when ?uestlove offered the searing "Who's Gonna Save My Soul." But for all their vaunted eclecticism, Gnarls sounded not-all-that-daring in comparison with everything that had come before. And Green and Burton no doubt learned a valuable lesson: In Philadelphia, never go on after the Roots.