I think that is Dock. It's not toxic but not recommended to feed. Some component of it is bad for torts in quantity... a bite here and there will be ok if your tort encounters it in an outdoor space. I pull it from my enclosure but it springs up so fast I've seen my tortoise take bites before I can get to it. It's a devil of a weed to get rid of!
I agree, it's dock. The seed spike contains hundreds of seeds, plus, if you don't get the complete tuber out of the ground when pulling, the piece left will sprout a new plant.
"Due to its potential to accumulate oxalates, all parts of dock, including its leaves, stems and seeds, are toxic."