Canna Seeds Viable for 600 Years - Interesting Web Site
In case you haven't stumbled across it already, there is an interesting web site called "Canna News" at http://www.clainescanna.co.uk/APage_News.htm
There is an interesting article near the bottom of this lengthy page about some seeds of Canna compacta that were found in an Inca tomb in Argentina. They were inside a rattle made out of a walnut shell. The walnut shell was 600 years old according to carbon dating.
These seeds were planted and they germinated! I used to wonder whether or not they would remain viable from summer to the following spring. I guess this would answer that question.