The term ALDER OR ASPEN is a crossword solution for the word TREE, which has four letters. Alder and Aspen are both types of trees that are found in many parts of the world. Alder is a deciduous tree that can grow up to 30 meters tall and is commonly found in wet areas such as near rivers and streams. Aspen is a type of poplar tree that can reach heights of up to 40 meters and is often found in cold climates.