The genus Salix has long and justly been considered a difficult one to study. It is not that the genus is so large, there being only some 200 living species known, or that these species are so variable in themselves, although a few of them are known to be very much so. The chief difficulty lies in the dioecious character of the plants, and the fact that in the majority of the species the flowers are produced before the leaves appear, or at least before they are large enough to become characteristic.
Proceedings of the Iowa Academy of Sciences
©1899 Iowa Academy of Science, Inc.
Ball, Carleton R.
"The Genus Salix in Iowa,"
Proceedings of the Iowa Academy of Science, 7(1), 141-154.
Available at: https://scholarworks.uni.edu/pias/vol7/iss1/19