Wednesday, December 9, 2020

SearchResearch Challenge (12/9/20): The mystery of the grape leaf polygonally changing color


A question I get asked a lot is... 

... "Where do you get your SearchResearch Challenge ideas?"  

As you know, our topics vary quite a bit.  One week it might be identifying a wreck that I spotted somewhere off the California coast, while another week we might be discussing the location of a mysterious statue in London, or small animals cutting a clearing around bushes in the Santa Cruz mountains. We get around.  

But the Challenges I like the most are those that come from friends who ask questions that seem simple or obvious, but which, upon closer examination, reveal hidden depths.  

I was email-chatting with my artist friend Lynne Garell who is living in France, loving life there, and taking wonderful photographs of the world around her.  

We started a conversation about one of her photos that caught my eye.  I've seen lots of leaves change colors over the years, but never quite like this: 

A grape leaf closeup. P/C Lynne Garell, from her series of grape leaf images 

This appeared in her blog, Lo Vedo Life, the other day and it seemed impossible.  How does this happen? How can a polygonal piece of a leaf all change at once?  Is this the way all leaves change?  What's going on here? 

Another image from her series: 

The more I looked into this, the more I realized that this isn't at all obvious... 

So I'm translating our conversation into an SRS Challenge for everyone.   Caution:  I have not yet figured this one out, so it might be REALLY  HARD or even impossible.  But that's the fun of the Challenge, is it not?  We'll set a high bar, and see if we can leap over it. 

1. What is this effect called?   (That is, the polygons changing color independently of the surrounding leaf to create this kind of pattern.)  

2. To answer this question for myself, I thought I'd first find out what each of those polygonal sections is called, and then search on that term.  But I couldn't find it!  So, a Challenge for you:  What is that part of the leaf called?  Here's an image that I made to illustrate the question: 

That thing...  what's it called?  These polygons, like the ones above in Lynne's photo, would seem to be fairly obvious structural features of a leaf.  But I can't figure out what they're called.  Can you?  (I realize that up close this looks like a giraffe's skin, but I assure you, this is a closeup of a leaf.)  

As always, I'm interested in HOW you found the answer!  Let us know in the comments section.   

Botanically yours... 

Search on! 


  1. Couldn't figure it out either. Searched for "leaf structure geometry" and by scanning images settled on "leaf structure voronoi", which led me to this blog post that tries to generate such leaf venation:

  2. Those leaf polygons- bullate?

    I started with "leaf parts". Moved from there to "leaf anatomy", finally putting in grape leaf. None of these really fit, but I clicked on this page-

    Which mentioned the leaf surface being "rough or 'bullate', or smooth."

    Since I had never seen that, I dumped "leaf bullate" into an image search. First Google asked if I meant "leaf bullet" which would have been a fun sidetrack, but I switched up to "bullate leaf" which gave me a ton of photos of those leaves with clearly defined cells.

    If you just type "bullate", there's lots of photos of motorcycles. Just so you know.

    1. "Bullate" is a defined area of a leaf, yes, but it's the curvature or the area (convex or concave) that makes it bullate. Bullate regions are also areoles, but not all areoles are bullate!

  3. I did my first approach to the Challenge in Spanish since the topic includes words not used in day to day life. Even in Spanish was difficult and slow with some words.

    My full process will be posted in another comment. I post this because maybe can help to move forward in the Challenge

    With [Patron nervios de una hoja] (Nerves patterns in a leaf)

    PDF What does a Scientist sees in a leaf. In Spanish

    Full article says: "Los dominios limitados por nervios se denominan aréolas"

    Mentions other data and also gives biography.

    Searching in English, found word is areole. Maybe this is a different part of the leaf. However, I understand this is the name we're looking to search for Q1

    1. Started with [Hojas plantas vid cambio color] and [Patrón hoja vid planta]

      Morfología de la Vid (Vitis Vinifera L.)

      Then reading this, tried the previous comment query. I did a mistake there. I wanted to say bibliography (or suggested readings) instead o biography.

      [Pattern Formation in Plant Tissue] Google suggested question and answer is: [What is pattern formation in plants?]

      [space between in leaf nerves is called] Lacuna

      [leaf areoles] on images

      Areole (areolate)

      [areolate leaf color changing]

      Autumn leaf color Wikipedia

      PDF Changing Colors of Leaves

      1997 what causes the leaves on trees to change color in the fall?

      Direct link search: WHY LEAVES CHANGE COLOR IN THE FALL a certain point which varies by species, some mechanism in the tree will trigger it to begin the process of closing up the veins to the leaves and eventually shedding them, lest they freeze while the veins are still open which can potentially harm the tree...."

      Searching for the name of the veins closing process name, found:

      Cells are responsible for most of the photosynthesis in the leaf and are called the palisade mesophyll.

      Out of topic and interesting too:

      Hundreds of volunteers are helping to map the Great Barrier Reef"

    2. Searched [Plant leaves autumn pattern]
      Venation pattern

      [Venation pattern unknown facts]

      Leaf venation patterns and principles of evolution in PDF and others seems interesting. Did quick search F9(areol) to read. It will be interesting to read and maybe, as one friend says, move the peanut forward in our Challenge

  4. Search: structure of a leaf
    Select Images tab
    Scroll to:
    Review Related Images and relevant terms;
    Answer: “leaf cell” (or “plant cell”?


  5. The polygon area is called an areole.

    I first searched for [grape leaf "fall color" polygon], which led to this photo of a sycamore leaf exhibiting an irregular fall-color pattern similar to that in the SRS question:

    The caption of this photo mentioned that the leaf had a “reticulate venation” pattern.

    [reticulate venation examples] gave nice photos/images of leaves, but no definition of the polygon.

    ["reticulate venation" leaf structure] led to the Wikipedia page for simply “Leaf” ( which contained the sentence: “The areas or islands of mesophyll lying between the higher order veins, are called areoles.”

    [areole leaf] led to this document that even included a grape leaf pattern similar to that in the SRS question: with the caption: “Leaf veins intersect to form enclosed areas called areoles.”

  6. After a red herring look through pavement cells and puzzle cells, [sections of leaf] led me to the onebox (do they call them that anymore?) which brought up the technical term, lamina, for the leaf blade.

    searches for [lamina subsections] and the like just led to cross-sections or different parts of the leaf anatomy, or segmented vs compound leaves.

    but! [leaf lamina composed of] led me to the wikipedia article on Leaf, of all things, which had this key sentence. "The areas or islands of mesophyll lying between the higher order veins, are called areoles."

    Now the problem with searching for anything related to areoles is that you get nipples, and even throwing in [leaf areole] or [chlorophyll areole] gets you cactus areoles, which are different. The [areolae mesophyll] gets us to "Leaf venation patterns and principles of evolution" ( , which is more of the level of what I was looking for to back up wikipedia. I'm just throwing mesophyll in there because it was mentioned as the spongy part of the leaf, so I hoped it would turn up other plant (and non-nipple) articles.

  7. I searched for leaf parts labeled, then leaf segments, then leaf segment closeup (because by now, I was using google image pretty much exclusively). One of the image's labels got me to search for leaf ribs, then leaf ribs I landed here, where I read about the kinds of ribs/venation in leaves. It seems to me that we have leaf structure divided by ribs (of varying design) so, "Mesophyll is the leaf's ground tissue".

    I also learned Major veins are not in contact with photosynthetic cells or to the intercellular spaces of the mesophyll, as they are surrounded by dense parenchyma.

    Minor veins are surrounded by small cylinders of dense parenchyma that form a bundle sheath around each vein. Bundle sheaths complete enclose each minor vein, all the way to the tip, and act much the way the endodermis of the root does: all photosynthates and other materials must pass through the sheath in order to get to the vein for transport, so the sheath cells act as a selectively permeable barrier, controlling the substances that the vascular system transports from the leaf.

    I'm making a connection between the minor venation and the fact that leaf color change has to do with the breakdown of chorolphyll (search: why leaves change color, site: to explain the segmented color. But that's my guess.


    The arrangement of veins in a leaf is called the venation pattern; monocots have parallel venation, while dicots have reticulate venation. Just what our Challenge is based on.

    Within each leaf, the vascular tissue forms veins. The arrangement of veins in a leaf is called the venation pattern

    netlike venation in this linden Just as in your pix.

    Did a lot of clicking til I found this Most Excellent Wiki:
    WIKIPEDIA: LEAF...smaller veins branch from the secondary veins, known as tertiary or third order (or higher order) veins, forming a dense reticulate pattern. The areas or islands of mesophyll lying between the higher order veins, are called areoles. Some of the smallest veins (veinlets) may have their endings in the areoles, a process known as areolation...Reticulate All veins branching repeatedly, net veined

    MESOPHYLL:...Most of the interior of the leaf between the upper and lower layers of epidermis is a parenchyma (ground tissue) or chlorenchyma tissue called the mesophyll (Greek for "middle leaf"

    So the polygons are not "things" so much as leaf/blade aress between the veins. As the leaf goes into senescence all goodness is pulled out and sent to the roots for storage over the winter.

    Excellent article here just published: NEWS RELEASE 26-NOV-2020 / Which factors trigger leaf die-off in autumn?
    Explains what the next part of the Challenge is likely to be.