Petunia may be fed, but... if you have bought it from a garden centre it will have been grown with pesticides and fertiliser that could harm your tortoise. Grow the plant on for at least 6 months in clean compost before feeding
https://www.thetortoisetable.org.uk/plant-database/viewplants/?plant=235&c=5#.XKpc4ozTWf0
I did some research and think it might be dwarf plantain?
Having resorted to Google, I agree that it probably is. We don’t get that in the UK unfortunately, so I don’t know if it is safe to feed.