When I talked about the Bristlecone Pines being the oldest known single organisms I mentioned that some clonal organisms were much older.
Here's a nice little slideshow about Pando, an 80,000 year old (give or take a few) grove of Quaking Aspen trees in Utah.
The grove which has about 47,000 stems connected by a single root system has spread over about 106 acres. The average age of the individual stems is about 130 years.
There's a link to an older article in Discover magazine which has more details on the clone, aging techniques used and some amusing stories:
Since my colleagues and I nominated Pando as the world’s largest organism, he has captured the attention of dozens of newspapers and radio stations across North America, and some of the reactions have been quite funny. Some see Pando as a threat: I received a call from someone asking, Does this giant clone, spreading vegetatively, pose a threat to the people living in southern Utah?