Taxonomy is a mess for Leyland cypress, X Cupressocyparis leylandii. The X preceding its genus name indicates that it is an intergeneric hybrid. Monterey cypress, Cupressus macrocarpa is the paternal parent of the original hybrid. Nootka cypress, Chamaecyparis nootkatensis, is the maternal parent. However, its name is now Cupressus nootkatensis.

Therefore, Leyland cypress is now Cupressus X leylandii, and an interspecific hybrid. It inherited attributes from both parents, as well as innate vulnerabilities. It can grow very vigorously to more than thirty feet tall in fifteen years. However, it may not live for another fifteen years afterward. It is very susceptible to cypress canker and a few other diseases.

This is why Leyland cypress often accompanies more permanent but slower vegetation. By the time it finishes its life cycle, the other vegetation is ready to replace it. Most large specimens are less than forty feet tall, with densely conical form. The evergreen foliage is grayish deep green. Less common cultivars are more grayish, yellowish or variegated.