My new word of the day is cupule (kyoo-pyool)

 Cupule is what the cap of the acorn is called. It is the modified hardened bracts. More than you wanted to know maybe. But when I started out on my walk today, I decided to see if I could see any big differences between the different species. One was hairier; some bracts were longer; some were curved inwards; and some were deeper.

The Bur Oak (Quercus macrocarpa) caps are pretty unmistakable in our area. They are the biggest at about 3 cm (1 1/2″) across and at the lower edges are hairy.

Closeup of a pair of Bur Oak’s cupules.
Post Oak (Quercus stellata) is what I have the most of at home. A common tree in the Cross Timbers with it’s rounded lobed leaves.

Closeup of the caps and leaf lobe of the Post Oak.

The Blackjack Oak (Quercus marilandica) leaves are recognizable by the bristles on the ends of lobes. It’s cap seem to curve inward at the bottom.

Closeup of Blackjack.

Chinkapin Oak (Quercus muehlenbergii) is less common in our area than some of the other oaks. It has  large toothed edges and narrows at the base of the leaf.

Closeup of the cap and leaf.

The Red Oak (Quercus shumardii) is a common tree in the area and popular in the nursey trade for it’s bright fall foliage. The Red Oaks in our yard were started from seed by Jim’s granddad.

It’s leaves are pointy and have bristle at the tips. The cap curves inward at the bottom.
Live Oak (Quercus fusiformis) is the evergreen oak. The leaves can have both smooth edges or a more holly-like leaf.  In the spring it pushes off most of leaves and produces fresh green leaves.

Closeup of Live Oaks cap and leaves.
Here are all six oak leaves and cupules for comparison. My sample size was small so not sure if the size and characteristics of the cupules are typical of each species. It should also be noted that there are other species of oaks in our area. These are just the ones at our house.

I bet you have noticed by now there were no acorns in the photos. That is because there were not any to be seen. All the critters got to them first. Maybe next year I will look at the acorns with their cupules.

Keep looking!


  1. This is a very helpful post, Mary! It's a great aid for oak ID in winter. It was pointed out to me long ago that the Shumard and Buckley oak cupules are very shallow – more than half of the acorn is (or would be) visible. I can easily see that in your photo of the Shumard cap. Thanks!

  2. Wow Suzanne! Thank you! It is a great compliment coming from you. Years ago when you did your winter tree bud class, it got me to looking at stuff like that. I wish I could still remember all that you taught. So thank you for all the classes you have led.

  3. That last photo of the composite of all is worthy of framing to a plant loving person!
    When I collected acorns last year to grow I didn't look at the caps as closely as you have shown us. I did notice the acorns have characteristic shapes though so there you go for next year, to include the acorn also. You may have to pick them from the tree because they are food for so many animals. That is how I got viable ones to grow. If they were loose in the caps I picked them. Often once they are on the ground, they are invaded by a weevil or other insect.

  4. Kathy,

    Thank you!
    I will keep you good gathering tips in mind next year. Your comments are very much appreciated. Thanks again!

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