Flowering and Fruiting
River birch is monoecious; separate male and female flowers are on the same plants. Clusters of poll en-producing male (staminate) catkins are formed at twig tips in fall and mature in April or May of the following year. Pollen production is abundant (birch pollen is a heavy contributor to the hay fever problem) (13). Female (pistillate) seed-producing catkins are borne on spur-shoots and appear with the leaves. The flowers open in early spring and the fruit matures in late spring or early summer. It is the only birch that does not produce seed in fall. Good seed crops occur almost every year.
Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods. Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965). U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.