According to the Internet's tubes, Pando, a quaking aspen colony (or clone), lives right here in good old Utah near Fish Lake. Pando is estimated to be anywhere from 80,000 to 1,000,000 years old, depending on which scientist (q.v. citation 18 & 19) you believe (or in this case, which Wikipedia article you believe.) Pando is also probably the world's heaviest plant/organism, with a estimated weight of 6,615 tons. Pando was, therefore, commemorated by the US postal service (scroll down).
I need to go back down to Fish Lake to photograph the great Pando, I think.