The Sinewy American Hornbeam

Photo by Richard Webb licensed by CC BY-SA 3.0

Winter is when I really start to notice trees. Admittedly, I am pretty poor when it comes to tree ID and taxonomy but there are a few species that really stand out. One of my all time favorite trees is Carpinus caroliniana.

Carpinus caroliniana goes by a handful of common names including ironwood, musclewood, and American hornbeam. All of these names have been applied to other trees so I'll stick with its scientific name. Finding C. caroliniana is rather easy. All you have to do is look for its unmistakable bark.

Photo by Rob Duval licensed by CC BY-SA 3.0

With smooth, sinewy striations and ridges, it is no wonder how this tree got the name "musclewood." The wood is extremely close-grained and is therefore very hard, earning it another nickname of "ironwood."They are generally small trees, rarely exceeding a few meters in height, though records have shown that some individuals can grow to upwards of 20 meters in rare circumstances. I hope that someday I will be able to meet one of these rare giants.

Carpinus caroliniana is also an indicator of fairly rich soils. Due to their high tolerance for shade, they are often a tree of the mixed hardwood understory. Their foliage resembles that of the family in which they belong, the birch family (Betulaceae).

Photo by Katja Schulz licensed by CC BY 2.0

The caterpillar of the io moth (Automeris io)

An adult io moth (Automeris io). Photo by Andy Reago & Chrissy McClarren licensed by CC BY 2.0

A multitude of insect species utilize C. caroliniana as a larval food source including the famed io moth. In the spring, male and female catkins are born on the same tree and, after fertilization, they are replaced by interesting looking nutlets covered by leaf-like involucres. The seeds are an important food source for a variety of birds, mammals, and insects alike.

The male flowers of Carpinus caroliniana. Photo by Philip Bouchard licensed by CC BY-NC-ND 2.0

Carpinus caroliniana is a tree I could never get bored with. Not only does it have immense ecological value, it is aesthetically pleasing too. Its small size and shade tolerance also makes it a great landscape tree in areas too cramped for something larger. Why this species isn't more popular in native landscaping is beyond me.

Photo Credits: [2] [3] [4] [5] [6] [7] [8]

Further Reading: [1] [2] [3]

Green Islands

Autumn is here and all across the northern hemisphere deciduous trees are putting on a show unlike anything else in the natural world. The range of colors are spectacular both from afar and up close. If you're like me then every single leaf is worth investigation. The trees are shedding their leaves in preparation for dormancy. The leaves aren't dying outright. Instead, the trees are reabsorbing the chemicals involved in photosynthesis as a way of getting back some of the energy investment that went in to producing them in the first place. 

If you look closely at some leaves, however, you may notice green spots in an otherwise senescent leaf. Why is it that certain parts of these leaves are still photosynthetically active despite the rest of the photosynthetic machinery shutting down around them? The answer to this question is way cooler than I ever expected. 

These "green islands" as they are called are almost always associated with an insect. If you look closely towards the base of these spots you will usually find a tiny leaf mining larvae of a moth busy munching away at the remaining photosynthetic tissue. The most obvious conclusion at this point would be to say that the moth larvae are the cause of the green islands. However, it is not that simple. 

When researchers raised the moth larvae under sterile conditions, they did not produce the green island effect. This proved to be a bit of a conundrum. Why would this happen in the wild but not under sterile conditions in a lab? The answer is bacteria. 

It would appear that the moth larvae have a symbiotic relationship with bacteria living on their bodies. These bacteria interact with the tissues of the leaf and alter the production of cytokinins. In the leaf, cytokinins inhibit leaf senescence. When the plant switches into dormancy mode, cytokinin production is shut down. The bacteria, however, actually ramp up cytokinin production throughout the tissues surrounding the larva. The result of which is a small region or "island" of tissue with prolonged photosynthetic life. 

Because of this, the larvae are able to go on feeding well into the fall when food would otherwise become nonexistent. By harboring these bacteria, the moths are able to get more out of each seasons reproductive efforts instead of simply stopping once fall hits. This is the first ever evidence of insect bacterial endosymbionts have been shown to manipulate plant physiology, though it most certainly will not be the last. 

I would like to thank Charley Eiseman for the use of this photo as well as inspiring this post. Charley is the man behind one of my all time favorite blogs Bug Tracks so make sure to visit and like Northern Naturalists.

Further Reading: [1] [2] [3] [4] [5]