All parts of the Sycamore contain a rich, sugary sap that is used as a sweetener in many foods and in brewing. As Sycamores readily absorb pollutants from the air, it is probably wise to avoid deliberately feeding leaves from trees that are growing in an urban environment where pollution can be high, although no harm will come if your tortoise nibbles a stray leaf or two that he encounters in his enclosure.
In Scotland the Sycamore is known as the Plane Tree, but this should not be confused with the London Plane, which is related to the Sycamore, but a different species.
Do not confuse with the American Sycamore, which is a type of Plane tree. See London Plane.