World's Oldest Plant.. "Question: How old is the world's oldest plant?
Answer: 43,600 years by carbon dating."

According to this site.

I would say that is pretty impressive; on the other hand, I think we cannot
really know for a fact that there's no older plant out there -- earth is a fairly
big place, and not every plant has been seen by people necessarily, let-alone
tested for age.

Now "oldest plant that we have record of age for" would at least have a basis...

Apparently on plant earth, finding something extremely old passes as a basis for
assuming it's the oldest, nowadays -- I for one wonder if there isn't a 50,000 year old
plant to be found out there.  ¶ 3:29 AM