A star-studded medley of musical guests played tribute to Pete Seeger at a benefit concert for the legendary folk singer’s 90th birthday.  Bruce Springsteen , Dave Matthews, Emmylou Harris, Ani DiFranco and John Mellencamp were among the 40 musicians performing in Madison Square Garden for the Sunday night show, a benefit to raise awareness for Hudson River Sloop Clearwater, an organization Seeger started to preserve and protect the Hudson River.  A lone light shone on Seeger as he opened the show playing a flute solo called “Menomonee Love Song.” As the lights came up, they revealed the outline of a sloop, fitting for an event dubbed the Clearwater Concert after the organization’s vessel, the gaff sloop Clearwater.  The crowd ranged from teens to octogenarians and perhaps even older. Springsteen brought them to laughter as he introduced Seeger.  “He’s gonna look a lot like your granddad that wears flannel shirts and funny hats. He gonna look like your granddad if your granddad can kick your ass,” the Boss said. “At 90, he remains a stealth dagger through the heart of our country’s illusions about itself.”  John Mellencamp came out early and performed, “If I Had A Hammer (The Hammer Song).”  “It was the very first song I learned how to play on guitar,” he said. Most of the evening consisted of multiple artists performing together with one highlight coming before the intermission. Pete Seeger joined by Emmylou Harris, Joan Baez, Billy Bragg, and others for a spiritual version of “We Shall Overcome.”  Arlo Guthrie, son of folk legend Woody Guthrie, was joined by the Preservation Hall Jazz Band for “Oh Mary Don’t You Weep.”  Tom Morello was the evening’s interloper, performing four numbers with different artists. The most impressive was his duet with Springsteen near the end of the show. The pair traded verses on Springsteen’s “the Ghost of Tom Joad.” The former Rage Against the Machine and Audioslave guitarist also performed “John Henry” with Tom Paxton, and “Waist Deep in the Big Muddy,” with Taj Mahal.  Dave Matthews told the crowd: “The first concert that my mother took me to was Pete Seeger.” Then he launched into a searing version of “Whiskey Rye Whiskey.”  Seeger and the rest of the evening’s performers came on stage for an extended cover of Woody Guthrie’s “This Land is My Land.” They came back on for several encores and at the end brought out the entire Seeger family.  Proceeds from the event will go toward preserving and protecting the Hudson River.