Botany word of the week.*

Marcescence

This is the retention of the dead and dry leaves (and sometimes other parts such as fruit or seed pods) on some deciduous trees through winter.  Persistence, or as I like to think of it: a relentless lingering, somewhat along the lines of my cat’s queries for elevenses, twelveses, oneses, twoses (you get the idea).  Some trees seem to exhibit marcesence as  a trait – oaks are apparently one of them, although our climate isn’t mild enough for most Quercus spp. so I can’t perform a decent study on multiple varieties.  I did take a wander past the row of bur oaks (Q. macrocarpa) that grow near the train station in my neighbourhood, and while there were a few single leaves straggling on the branches, the trees were pretty much completely bare.  But we have to count that as an insufficiently representative sample (which, incidentally, also seems to be my cat’s views on the amount of food I give her).

IMG_3354

There are several theories on what causes marcescence, and what purpose it serves.  I believe in the case of this elm tree (and others like it in our city), the early frosts and severe cold we received back in September led to a failure of the formation of the abscission zone.  (This is an area of separation created by the natural weakening of cell walls between the petiole and the leaf.  While deciduous trees abscise in autumn, conifers do it pretty much all the time.  Another big difference is that deciduous trees normally fling everything off and conifers are, well, waaaaaaay more reserved). The leaves in my photo basically died on the spot and the tree wasn’t quite ready for that to happen. The wind took most of them off but some are still hanging around, waiting for spring like the rest of us.

Some researchers speculate that marcescence is a defense mechanism for the tree, protecting it from the munching of herbivorous predators such as moose and deer (who are going to eat fresh, tender young branch tips over icky dry foliage every time.  You can’t blame them, really).  Another idea is that the dry leaves act like little windproof shawls for the leaf buds, protecting them from winter desiccation.  Perhaps.  Still another thought is that the trees are deliberately generating their own mulch, dropping it at just the right time – spring, not autumn – for maximum moisture retention and as a source of nutrients.  Far-fetched?  Maybe, maybe not.

So what happens in the spring, when the buds of the new leaves break?  The marcescent leaves may remain on the tree, still waiting for a really strong wind to snap them off, or they may be pushed off the tree by the new growth, in which case they are instantly sucked up into a magical vortex so that you never have to rake them up.  

Then again, there are never any guarantees when it comes to magic, so have that rake handy, just in case.

Sources:
Finley, Jim. “Winter Leaves that Hang On.” PennState College of Agricultural Sciences. 2012. https://ecosystems.psu.edu/research/centers/private-forests/news/2012/winter-leaves-that-hang-on.
Gast, Richard. “Marcescence: An Ecological Mystery.” Adirondack Almanack. November 19, 2017. https://www.adirondackalmanack.com/2017/11/marcescence-ecological-mystery.html.

*To be completely truthful, I’m not sure which specific day of the week the Botany Word of the Week will be posted.  Or that it will actually be posted weekly.  It may kind of float around and periodically pop up and surprise you.  Hopefully that’s okay.  

15 thoughts on “Botany word of the week.*

  1. This is what makes valley oaks so messy through winter. They can defoliate thoroughly if they get cold enough. For sweetgum, retention of colorful foliage as late as possible is a desirable trait. It gets cool enough for them to color well here, but not cold enough to ruin the foliage. However, I think it can look odd if they are still colored late in winter. Some of ours are still rather green.

  2. I observe thus every year on our beech trees and beech hedge but never had a word for it. So thanks Sheryl! Personally I believe it has no function at all, or all beech would do it, wouldn‘t they? We have a row of them and only about half are completely bare, some shedding all their leaves really early. Look forward to learning more new words. 🙂

  3. I, too, never knew there was a term for this, but all the oaks and beeches are a beautiful example of
    marcescence. I’ve written it down so that I can look it at from time to time to remind myself of it. Now that I am in my sixties, my short-term memory isn’t as sharp as it once was. But if I write a word down and look at enough, eventually the meaning and the word will come together.

  4. I loved being introduced to this new word, and I loved that I already knew ‘abscission.’ Word by word, we learn. This was a fascinating post, and I’ll certainly look forward to more.

  5. Good word, Sheryl. I know that here, beeches only retain their leaves through the winter when they are small or when they are used as a hedge and kept small on purpose. Young oaks do it as well.

    • Thanks so much; I’m so glad you enjoyed it!

      Thank you as well for letting me know about the email share link – I tested it and it seems to be working fine on my end, but I’ll see if I can get a few other people to try it from other email addresses (maybe it depends on the service provider?). It’s a WordPress feature so if it is truly acting up then I will have to contact them. Have a wonderful weekend!

      • An update: the email link seems to only be working for me! I will have WordPress take a look. Thanks so much for letting me know – I wouldn’t have checked this on my own and it could have gone on this way for a very long time.

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