Male catkins are formed on twig tips in the fall and mature the
following April or May. Female catkins appear with the leaves and open
in early spring. The fruit matures in late spring or early summer, and
is dispersed upon maturity .
- 13. Grelen, H. E. 1990. Betula nigra L. river birch. In: Burns, Russell M.; Honkala, Barbara H., technical coordinators. Silvics of North America. Volume 2. Hardwoods. Agric. Handb. 654. Washington, DC: U.S. Department of Agriculture, Forest Service: 153-157. 
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