I've just eaten a mandarin orange and the small star shaped thing at
the end of the fruit, was left on my desk, I wondered what it was
called? I assume it's where the fruit was initially attached to the
tree

A citrus fruit is technically a hesperidium, and the thing left
at the end is the receptacle with attached calyx (sepals).

-Philip

wrote:
I've just eaten a mandarin orange and the small star shaped thing at
the end of the fruit, was left on my desk, I wondered what it was
called? I assume it's where the fruit was initially attached to the
tree