Sienna Glen maple (Acer x freemanii 'Sienna') is a hybrid maple tree that is known for its excellent autumn color and adaptable nature. In terms of size, Sienna Glen maples typically reach a mature height of about 40 to 50 feet (12 to 15 meters) with a spread of 30 to 40 feet (9 to 12 meters). It is considered a medium-sized tree and forms an upright, oval-shaped canopy. Keep in mind that the actual size of the tree can vary depending on growing conditions, soil quality, and climate.