Although Shepherd's Purse is a member of the brassica family, and therefore contains goitrogens, it is fine to feed to your tortoise in moderation.
Please be aware that two or more
goitrogenic plants should not be fed in conjunction with each other, and
the sum total of goitrogenic foods should not exceed the guideline for a
single plant of 'in moderation' (amber-green) or 'sparingly'
(amber-red). This will ensure that goitrogenic consumption stays within