Wednesday, October 9, 2013

The sedge masquerading as nutsedge

Yesterday I did a Sherwood Fox Arboretum tour with a group on campus (the Senior Alumni). We walked around a tiny corner of the campus, talked about a bunch of trees (but certainly not all!) that we saw on the way, they asked questions (I tried my best to answer most of them!), we laughed at my silly jokes, and then we all went on our merry way. If you're here reading my blog because I told you about it yesterday, welcome! I'm glad you found it. To the rest of the almost 21,000 of you that have discovered my blog: you're awesome! Thanks for helping make my "little project" turn into a rather large project read worldwide. I appreciate your eyeballs glancing over my blog every so often :)

Species name: Cyperus sp. (probably Cyperus strigosus)

Common name: false nutsedge

Location: Western University campus

Sedges are neat and wonderful plants, but most of them get completely overlooked by the average person. They are relatives of grasses (in that they're in the same order of plants, which I guess would make them cousins in a way), along with rushes, but have one notable characteristic that distinguishes them from the grass family. More on that later. A lot of people, even a lot of professional botanists and a lot of amateur botanists, completely ignore sedges (any kind of grass, really) when coming up with plants to identify because they're just so gosh darn hard to ID without a microscope. There are so many species of grasses and grass relatives that it is incredibly easy to misidentify them. There are only a few subtle characteristics that can be used to identify different species of grasses and sedges, most of which require the use of either a dissecting or compound microscope. Characteristics like the shape and size of the flower (in this species you can see the flowers in the bottom picture; they are about 1 mm long and are yellow, with the white stamens sticking out to disperse pollen), and the shape and size of the pollen grains (not pictured since that requires a microscope to see, and that would have required me collecting the plant which I don't normally do). Since I have neither of these to work with, the best that I can do is a "best guess" based on habitat (a place that regularly gets wet, and can be quite swampy at times), country location (North America), and colour of the flowers based on the time of year (many turn brown as the seeds mature, and seed maturation is in the spring for some species, the summer for others, and the fall for yet others). I know I definitely have the genus correct, this is most certainly a Cyperus. I'm also pretty certain about the species name (C. strigosus) because of the presence of wispy leaves at the bottom of the stem (many sedges only have leaves under the flowers, not also at the base of the stem), and the general shape of the inflorescences or the flower heads.

If I am correct about my identification, this species of sedge is native to North America, from Canada all the way south to parts of northern Mexico. It prefers disturbed areas, as this species is only good at competing for resources with other plants when there is low diversity and a large amount of available light. This is the same as many species of sedge; in established meadows it is rare to see a lot of sedges (although, at the periphery they might lead you to believe they might be common, since edge habitats are disturbed areas by definition). In areas of bare soil (like newly tilled agricultural fields or even backyard gardens), it is common for this plant to invade and spread rapidly. It can become invasive in some areas that are under constant states of disturbance, and is also considered an agricultural pest.

So what makes sedges, as a group, interesting? They look a whole lot like grass, and with one exception have no major economic value. The fascinating part about these plants is their stem structure: it's triangular. If you make a cross-section of the plant, it is incredibly obvious that the stem is triangular (mint stems are, as a general rule, square but some species have "rounded square" stems so you have to use your imagination a bit to see the square; this is not the case with sedges. They all have distinctly triangular stems). You can even tell that the stems are triangular in the middle picture by looking at the leaves emerging from just under the inflorescences: the largest leaves all radiate outwards from each edge of the triangle, and the smaller leaves under them radiate outwards from the three corners of the triangle stem. If you think about it, maintaining a triangle during growth would be incredibly difficult. The more you push the sides of a triangle outwards to "make room" for stuff on the inside, the more it becomes a circle. You'd think that after the stem was finished growing, it should be completely cylindrical and only have three ridges or bumps where the triangle's corners used to be. That's not actually what happens, since fully-mature sedges still have triangular stems. Plants aren't as simple as we think they are!

I mentioned somewhere up there that there's only one economically important sedge. Even at that, the economic importance of this species is significantly less than what it once was. I'll give you bonus points if you can figure out what it is (these points can be added to other hypothetical points you get in other places. You know, like bonus points you get for doing the dishes or walking the dog without having to be asked. Those kinds of points).

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