* Formal name: When referring to the species *Acer saccharum* (its scientific name), you'd capitalize "Sugar Maple."
* Common name: If you're using it as a general description of a maple tree that produces sap, you would not capitalize it ("sugar maple").
Examples:
* Formal: "The Sugar Maple is a popular tree for its beautiful fall foliage."
* Common: "The forest was full of sugar maple trees."
Hope that helps!