 "Pseudotsuga menziesii" is widespread in western North America and is an important source of timber.The number of species has long been debated, but two in western North America and two to four in eastern Asia are commonly acknowledged.Nineteenth-century botanists had problems in classifying Douglas firs, due to the species' similarity to various other conifers better known at the time; they have at times been classified in "Pinus", "Picea", "Abies", "Tsuga", and even "Sequoia".