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Paper Birch Catkins: Winged Nutlets & Bracts Dispersing

12-8-15 white birch female catkin 005Paper birch (Betula papyrifera) 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 lack petals, enhancing wind pollination. After fertilization occurs, the male catkins wither away, while the female catkins droop downward and become cone-like.

The female catkins consist of tiny winged nutlets that are located behind three-lobed, hardened, modified leaves called bracts (yesterday’s blog post) and 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.

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8 responses

  1. I so enjoy seeing these and other seeds begin to pile up on snow (in a more normal year) and become a winter-long layer of duff. Thanks for your continued, informative writing, always a delight.

    December 10, 2015 at 7:23 am

  2. Cheron barton

    Our friends in the neighborhood are busy!!

    Sent from my iPhone


    December 10, 2015 at 7:24 am

  3. Marilyn

    I haven’t been up-and-personal with a paper birch since I was a kid. It’s all gray birches around here any more.

    December 10, 2015 at 8:09 am

  4. Kathy

    Just a note that the leaf in the picture looks like gray birch. Is that the same as paper birch, because I thought Paper birch was the same as white birch?

    December 10, 2015 at 10:53 am

    • Hi Kathy,
      I’m so glad you wrote. I determined the species by the shape of the winged seed, but on re-checking, I see that you are right — the bracts of white/paper birch and gray birch are very similar, but there are differences, and the leaves are quite different — I was so focused on the catkins I didn’t even give a second glance to the leaf! I shall make note of this in tomorrow’s blog! Thanks again.

      December 10, 2015 at 7:09 pm

  5. this looks like a grey birch leaf, but knowing that paper and grey birches do hybridize I wonder…do their bracts/seeds end up looking more like one species than the other?

    December 10, 2015 at 9:01 pm

    • You are right – it IS a gray birch, but I can’t answer your interesting question about the appearance of hybrid bracts/seeds, because I don’t know!

      December 11, 2015 at 7:45 am

  6. Guy Stoye

    Mary Very sorry I tried several times to donate $40. but Google Chrome and the auto-fill just freaks me out and I’m out of time this afternoon. Will try later. Guy Stoye I don’t understand Google Chrome.

    March 11, 2016 at 3:11 pm

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