The Hawksbeard is one of those plants with 'yellow flowers' that we often hesitate to feed because we can't be sure of their ID.
However, there is one way to be certain you have one of the Hawksbeards: if you look below the flower you can see there is a plain ring of leaf-like bracts that stand out from the rest.
The photo below, of Hawksbeard and Sowthistle flowers, clearly illustrates this feature. Most of the Hawksbeards have this trait. Other characteristics include the fact that the base of the leaves clasp the stem (as opposed to being on a stalk), and that leaves get more narrow as they go up the stem. In the early stages of growth they form a rosette on the ground and strongly resemble Dandelion plants.
Hawksbeards are one of the plants that is safe to offer in the tortoise diet.