A Frankenplant or the real thing?

Species name: Hydrangea quercifolia

Common name: oak-leaved hydrangea

Location: Ontario

Those of you who have never seen this plant before probably looked at the leaves and thought "hey! I recognize those! That's an oak!" and then looked at the next two photos and thought "gee, she's awfully good at photoshop. Those leaves and flowers don't belong together!" Well, you would have been in good company in that boat of confusion; when I first saw this plant a couple of years ago I thought someone had created a Frankenplant by grafting two completely different species together (which is possible, but usually they're at least in the same or closely related families. Hydrangeas and oaks are nothing alike, and don't share a recent ancestor). The oak-leaved hydrangea is a real plant, "created" as a product of evolution and natural selection, not garden novelty and artificial selection. It is native to North America as far north as Tennessee and as far south as Florida, from the eastern seaboard all the way west to about Louisiana. It can grow quite happily in southern Canada despite our cold winters as long as it is either drastically cut back in the spring to prune off all the dead growth (the winter will kill any overwintering buds; most of the new growth comes from the rootstock in Canada), or planting it in a very sheltered area from the harsh winds and the weight of the snow. Building a "burlap teepee" to put over the plant to protect it during the winter would be a good thing if you plan on keeping it around for a while; if not just a good hard prune in the spring and you'll be good to go. Just don't expect many flowers since those only grow off of at least one years' growth.

The oak-leaved hydrangea is a perfect example of phenotypic plasticity; that is, a plant's ability to modify its appearance based on environmental conditions. Often, this is a slow process involving changing growth patterns over weeks or even months, but in the oak-leaved hydrangea during peak growth times it can be in as little as hours. During times of drought, the plant actually has the ability to reabsorb nutrients from its flowers to put back into the leaves and sustain its basic life functions: making sugars from water and carbon dioxide, then breaking down that sugar again into energy. The flower buds will look completely healthy, but if the plant is experiencing a prolonged drought then all of a sudden it seems like the buds are withering and they turn brown. Those buds will never develop into flowers, but if you give the plant a good watering as soon as you notice it, new ones might form if you're lucky. The plant can also modify the appearance of its leaves; after a prolonged drought the leaves will be more prominently lobed with less leaf area. If the growing conditions are ideal, then the leaves will be much fuller with more tissue between the main veins. You can almost think of it like the difference between a pin oak leaf (which you can see HERE) and a white oak leaf (which you can see HERE). A pretty drastic change!

The pin oak

Species name: Quercus palustris

Common name: Pin oak

Location: Ontario

My friend Tanya demanded more native species in my blog, so here we go! Another native tree, just for Tanya. The pin oak is just barely native to Ontario; the native range extends only as far north as my hometown so I guess I should be considered lucky! The native range extends quite far south, as far as Georgia and all the way west to Oklahoma and Kansas. In Ontario this tree is relatively rare except where planted for ornamental value, and it's difficult to say what might happen with climate change. Species ranges are expected to move towards the poles (so in this case, north) but one also has to keep competitive ability in mind before you make those kinds of assumptions. The pin oak is an incredibly poor competitor, especially when it comes to shade and moisture. In the spring, during the seasonal flooding periods, the pin oak is incredibly tolerant of being partially submerged, and opts to set leaves later in the season once the ground is drier. During the growing season, however, the pin oak is very intolerant of standing moisture around the trunk, and any moisture at all towards the base of the tree often leads to severe decay. Unlike most other oaks, the pin oak doesn't have a large taproot that it uses for underground support; instead it has a very shallow root system that stretches over a large area. Once the bottom of the trunk is rotten, the tree no longer has a support system and it is prone to being blown over during any kind of severe weather. This tree is also very shade intolerant; even small shrubs can out-compete this tree for resources when young. It just doesn't seem to have the ability to push up out of the lower canopy, even though the potential height of this tree is 60 feet or more.

I guess this is the first blog post where I have to admit that my plant identification skills are sometimes aided just by the location that I'm in. My hawk-eyed blog readers will notice that there's a post coming out of the ground in front of the tree with an information plaque on the top. All of Western University's campus is an arboretum, which is basically an outdoor museum of living plants. It's not quite a botanical garden, since botanical gardens often have public greenhouses associated with them (we don't), but they also have ALL plants labelled to the species level. At Western, it's only the trees that have labels, not all plants. The label contains the common name, the species name, the family that the species is in, and soon will have information about whether or not the tree is native, and whether or not the tree is considered invasive. It's incredibly convenient being able to walk around campus and learn about plant identification; you can actually walk up to the trees and touch them, smell them, feel their bark, break open young twigs to see what colour they are, etc. It's also incredibly helpful to be able to see a tree through the seasons, which can also help with remembering names of trees.

But back to the pin oak!

The uses of pin oak are many aside from the ornamental value of this plant. The pin oak is actually one of the many reasons why we now have an entire field of work called "forensic botany"! Sometimes the pin oak is sold as lumber under the name "red oak," which as you know is a completely different species. If it stopped there, then I wouldn't really see a problem. But in reality the wood of the pin oak is much weaker compared to the red oak, has much less of a desirable colour and grain pattern, and has many, many more knots in the wood than a red oak would. Using this species in place of red oak could lead to disastrous consequences, depending on the intended purpose of the wood. The best use of pin oak wood is as firewood, or to make wooden pins for building construction (where the common name probably originates). It is also a medicinal plant, having been used historically in a tea used to treat intestinal and abdominal pain.