Leaf characters, unlike stem characters, are as a rule subject to such variations that they form an unreliable basis of comparison between plants. Conifer leaves on the contrary, because of their simplicity as compared with other leaves, show a large degree of uniformity, particularly in those characters seen in cross section.
Proceedings of the Iowa Academy of Science
©1916 Iowa Academy of Science, Inc.
Durrell, L. W.
"Notes on Some North American Conifers Based on Leaf Characters,"
Proceedings of the Iowa Academy of Science, 23(1), 519-582.
Available at: https://scholarworks.uni.edu/pias/vol23/iss1/64