Science lesson: marcescent leaves

by Caroline Brown

Marcescence is when a plant part dies but is not shed. It’s most frequently noticed in the winter, when certain deciduous tree species don’t lose their dead leaves. Oaks and beeches have normally marcescent leaves. That’s an oak at left, and marcescent beech leaves are pictured below the jump.

Most deciduous trees lose their leaves when they are no longer photosynthesizing, the process by which a plant gets nutrients. When photosynthesis slows in the fall, the base of the leaf stem produces an enzyme that forms a separation layer, known as the abscission zone, which prevents infection and eventually causes the leaf stem to separate from its branch and fall to the ground. This process is called abscission.

Marcescent leaves don’t form an abscission layer, and only drop in heavy winds or when new leaf buds push them off in the spring. It’s not known exactly why marcescence occurs. The hormone that stimulates abscission is called ethylene. It is believed that the hormone auxin inhibits abscission by preventing the abscission layer from forming. But no one seems to know why some trees are normally marscescent and others aren’t.

Enjoy the texture that the papery, withered leaves bring to the otherwise somewhat two- dimensional winter landscape, courtesy of marcescence.

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10 Comments to “Science lesson: marcescent leaves”

  1. Very interesting reading. We have a few trees around town that don’t lose their leaves and I’m sure they are beech trees.

  2. I have always wondered why my Viburnum Lantana never sheds its leaves. Now I know why – thanks for the good explanation!

  3. I had often thought that not shedding leaves was a sign of poor health – but it seems that it’s not such a big deal. I like having some dry leaves around up there! I like how they rattle in the wind, it’s one of those classic spooky Halloween-time sounds.

  4. So that is why my oaks drive me crazy! They’re huge and very old and it takes the entire winter for them to shed all the dead leaves. Thanks for putting a name to it for me.

  5. Great explanation. Thanks for sharing that interesting information — now I understand why some of the trees such as my Burr Oak don’t shed all their leaves.

    PS: thanks for faving me over at Blotanical. I have no idea how to fave you back and have just sent a note to Stuart asking him how I can delete myself from Blotanical or if he would do it for me. I really dislike that site. I much prefer visiting people’s blogs and reading their interesting content and viewing the lovely photos — that way I can leave a note too!

    This was a very interesting post — thanks!

    Diane

  6. I’m enjoying the posts on trees and I like the photos. You’re definitely encouraging me to learn more about ecology and not focus entirely on agriculture.

    There were many trees like that in the mid-Atlantic. Up here everything is covered in snow.

  7. Hi Caroline! One of the most distinctive things I first noticed about Pennsylvania forests is the delicate “blush” that the marcescent young beeches lend the grey-brown forests all winter. This year I noticed even more trees holding there leaves (although wind has since stripped most of the oaks bare).

    Thanks for this informative post,
    Jade

  8. I have a garden surrounded by beech hedges that hold their leaves all winter. I haven’t come across the term marcescent before, so thanks for the very informative post.

  9. Thanks so much for this post! The children just asked why one tree in our yard did not loose its leaves…now I have an answer! Love your blog….great info as we work on our learning center garden!

    All the best
    Ms Jan

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