Reese Witherspoon sings 'Sweet Home Alabama' for 40th

Birthday gal Reese Witherspoon treated her guests to something special Saturday night at a Hollywood club.

The Sweet Home Alabama movie actress, who turns 40 on Tuesday, brought her mom along for the fun. Among the other attendees: Kate Hudson, Taylor Swift and Laura Dern.

Keith Urban was on guitar during the proceedings on stage and at some point, party girl Swift also took to the microphone. Swift had spent the previous night dancing and singing with friends on the floor of the Las Vegas club where her boyfriend, Calvin Harris, had a show.

Vanity Fair writer Derek Blasberg posted a video of Reese's performance of the Lynyrd Skynyrd song of the same title as the movie  on Instagram. He wrote, "You can take the girl out the South, but you can't take Sweet Home Alabama out the girl! HAPPY BIRTHDAY." Check out Urban behind the, ahem, singer.

Witherspoon posted a video of her and her mom, Betty, on the way to the party.

Guests posted selfies that included celebrity friends.