I decided to make some stellations.
These are sweetgum (Liquidambar styraciflua) leaves. They are quite common here in the Eastern US and give us some very nice Fall color.
1. These tufts of hairs are called domatia, which means little houses. As far as biologists can tell their only purpose is to provide shelter for mites. Think about that: the tree grows little homes for other living creatures! The thought is that the mites sheltered by the domatia are beneficial to the sweetgum tree in that they eat herbivores or fungi that would attack its leaves. The whole story may be much more complex. (See this study of avocado domatia for example.) Do the domatia perhaps harbor harmful mites as well as beneficial ones? In any case, domatia on leaves fascinate me.
2. Chloroplasts appear to still be alive and well in at least this portion of the leaf. Chloroplasts are awesome. (The main reason I’m pointing this out is that my kids insisted that I draw an arrow to the green portion of the leaf.)
3. You may know that yellows, browns, and oranges are present in the leaf during the summer, but are masked by the green chlorophyl. This is not the case for purples and reds, which are pigments produced in the leaf (see fall color on Wikipedia where there is also a nice discussion of possible benefits to the tree of fall coloration.)
4. The patterns of veins in the leaves is called venation. Note that, as highlighted in the blow-up, the leaf veins do not spread as what mathematicians and computer scientists call a “tree” but form many small loops.
Here are some more sweetgum leaves from my wood lot:
I believe, but I’m not totally sure that I have Chestnut Oak (Quercus prinus) and Swamp Chestnut Oak (Quercus michauxii) growing in my backyard. The two leaves on the left I think are Swamp Chestnut Oak. The leaf on the right (which is showing it’s underside, whereas the others are showing their uppers) I think is Chestnut Oak. I’m not the only one to confuse the two: confusion of the two species mentioned on Wikipedia.
1. These closely related species have wavy leaf margins. Why? I have no idea.
2. Two of these leaves have what appear to be galls. What are galls? They are abnormal growths on plants. They come in a huge variety of shapes and sizes (see this gallery of galls). Many (including these ones it appears) are caused by insects depositing eggs in the plant. Somehow the local plant tissue is reprogrammed to grow the gall. The gall provides the young insect with food and shelter. Does the plant get anything in return? I’m not sure.
3. It appears that the gall on the lower leaf has a leaf mine emerging from it. In other words, it looks like the young insect (or maybe it was a mite) emerged from the gall and tunneled through the leaf, eating as it went. In the enlargement I’ve highlighted the path of the mine from the gall to the place where the insect mined in a little loop.
Check out this Q&A about galls and leaf mines.
4. My kids insisted that I show this gall detail, and for good reason! It is very intricately marked with light and dark squiggles. What could cause this? Does the marking serve a purpose? What mathematical models describe the marking?
5. Some leaf feeders skeletonize the leaf. They leave behind only the veins. These patches of skeletonization probably happened on the living leaf. Once leaves die and start to decay on the forest floor, they often undergo more skeletonization.
6. Some leaf-feeders eat holes in the leaf. Birds often find insects to feed on by looking for leaf damage, or maybe even by looking for the shadows of damaged leaves (thence finding the damaged leaves themselves and finally the invertebrate doing the damage).
I have some puzzles left over from the Government Shutdown. Plus, I’m working on some more for starter activities for my wife’s engineering class, so enjoy! Solution is here
Shown is a mockernut hickory (Cara tomentosa) leaf from a young tree in my back yard. I plucked the leaf so that my kids could feel that it is fuzzy underneath, which is how you know it’s a mockernut and not some other hickory species.
Some features of the leaf pointed out in the picture:
1. This is one leaf made up of five leaflets. As far as I can tell scientists are still puzzling over why some plants have developed compound leaves, while other plants have simple leaves. Here is one hypothesis. Are there other mathematical models that can help us understand compound leaves?
2. Many species of insects “mine” leaves. As larvae they live inside the leaf and eat away at the leaf’s insides. These mines may have been made by moth, sawfly, fly, beetle, or wasp larvae. What rules does the miner follow to determine the shape of the mine? Can we model it mathematically?
3. I’m not sure why leaf edges of some plants are toothed while those of others are smooth, but botanists have discovered that there is a correlation between leaf-margin toothedness and climate (particularly mean annual temperature). The more toothed leaf species present, the colder the climate. So fossilized leaves can be used as a sort of thermometer frozen in time.
See for example: leaf margins and climate.
4. Insects that eat leaves are an important link in the chain that passes energy from the Sun, to plants, and then to animals. When you see leaf damage like this think of it as energy being harvested to fuel bird flight.
5. This leaf is changing from green to yellow to brown for the Fall. As circulation to the leaf shuts down, chlorophyl breaks down and is not replenished. We can understand how and why leaves change color, but why is it so beautiful to us? Maybe what matters is that it is beautiful to us.
6. The stalk that attaches the leaf to the stem is called the petiole. In some plants leaves have no petiole. In some other plants the petioles have no leaves! Hickory has both a fairly long petiole and substantial leaf.
7. These leaf spots are probably caused by a fungus or a bacterium living in the leaf. The parasite probably doesn’t provide any benefit to the hickory tree, but it doesn’t cause much damage either. Parasites don’t usually engender warm fuzzy feelings in us. Arguably, there is good reason for that. Then again, they are fellow creatures trying to make a living. If they’re not doing much harm that’s probably more than we can say for ourselves. Who are we to deny them? Maybe the biodiversity they add provides something to the ecosystem that we’re not seeing yet. What probability distribution might the size and frequency of the leaf spots follow?