We have not heard of toxic reactions in tortoises from the majority of Chrysanthemum species, so you can feed most species of this plant in moderate or small quantities and as part of a wider varied diet.
The stems and leaves of Chrysanthemums can cause severe allergic reactions in cats.
N.B. Two members of the Chrysanthemum family (Chrysanthemum cinerariifolium and C. coccineum) contain high levels of Pyrethrins which are used to make an insecticide that can be harmful to reptiles, so you should not feed those species of Chrysanthemum to your tortoise. Please make sure you identify your Chrysanthemum correctly and if in doubt do not feed to your tortoise.