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Archive for December 28, 2020

Paper Birch Seeds Dispersing

Paper Birch (Betula papyrifera), also called White Birch, produces separate male and female flowers on the same tree, both in the form of catkins (cylindrical clusters of flowers). The catkins form in the fall and overwinter in a dormant state. In the spring they mature as the leaves develop, becoming pendulous. Male catkins are 2-4 inches long, whereas female catkins are usually 1–2 inches long. Both male and female flowers lack petals, enhancing wind pollination. After fertilization occurs, the male catkins wither away, while the female catkins droop downward and become cone-like.

The mature female catkins consist of tiny winged nutlets that are located behind three-lobed, hardened, modified leaves called bracts. Both winged seeds and bracts are usually dispersed by the wind during the fall and early winter. Birch bracts are species-specific — different species of birch have different-shaped bracts, allowing one to identify the species of birch that a bract comes from. Those of Paper Birch (pictured) look somewhat like soaring birds.

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