I was lucky to find petrified leaves (in a rather hard stone) on a small mountain called 'Roter Berg' in the outskirts of Vienna, the red radiolarites from this mountain were prehistorically used for making spearheads and blades.
In some soil layers there were found ammonites too.
The plant remains are dated 8,9-9 Million years old and stem from the Pannonium (11,608 - 7,246 million years before present).
They may present Lythraceae.
Here the microscopic pictures: