That is spotted spurge. It is a favorite with desert tortoises because it is a plant that grows in the desert where the tortoises come from. However, it is high in oxalates and not really a favored food.
We have a resource right here on the forum under the Tortoise Diet and Food category:
Yup...we have a variety of spurge that grow wild here and at certain times of year the men here will partake....but usually near the end of the summer...