There have been several seeds known at different times as the oldest viable seed.
Narrow-leafed campion (Silene stenophylla) (wild)
The Judean date palm "Methuselah" at Ketura, Israel
Sacred lotus (Nelumbo nucifera) (wild)
The Judean date palm is a date palm grown in Judea. It is not clear whether there was ever a single distinct Judean cultivar, but dates grown in the region have had distinctive reputations for thousands of years, and the date palm was anciently regarded as a symbol of the region and its fertility. Cultivation of dates in the region almost disappeared after the 14th century AD from a combination of climate change and infrastructure decay but has been revived in modern times.
The Judean date palm at Ketura, Israel, nicknamed Methuselah
Vespasian coin celebrating the victory over the rebels. The legend says: IVDEA CAPTA ("Judaea [has been] captured")