What does purple sap from a Maple tree mean?

Purple sap from a maple tree typically indicates the presence of a fungal infection, particularly from the fungus known as Hypoxylon corticale. This condition can occur when the tree is under stress, possibly due to environmental factors like drought or injury. The discoloration in the sap may also be a response to the tree's attempt to seal off the affected areas. It's important for tree health to monitor and manage any underlying issues that may be contributing to this phenomenon.