What Makes an Orchid an Orchid … Part 2 (Bi-lateral Symmetry)

Now, continuing on with the Orchids101 section, we come to "bi-lateral symmetry." The easiest way that I can describe bi-lateral symmetry is first to talk about symmetry and then add bi-lateral to it and then show how it applies to orchids.

First, symmetry is taking a shape or object and drawing a straight line through it's center. If both halves are equal it is said to be symmetric. I'm sure there is a more mathematic way of describing symmetry, but this is an orchid blog not a math blog. :) A crude example would be:

Now to add bi-lateral to the mix. There are two common types of sym

metry when talking about flowers: bi-lateral (which we'll talk about in a second) and radial symmetry. I would say radial symmetry is probably the type of symmetry we would think of most when looking at flowers in general. Radial symmetry is symmetry where flower structures will be symmetric when drawing a line from it's center. In this example, a daisy, each petal is symmetric to itself when a line is drawn through it. It has a very well defined center in which the petals "radiate" out from:

Bi-lateral symmetry is when the line can be drawn through the flower in only one way to create a symmetrical image. In Michigan we have natively growing lady slipper orchids (Cypripedium) that I will use for the next example:

As you can see, above, there is only one possible option for line to be drawn to make both sides symmetrical. In this case, it happens to be straight up-and-down which is the most common way in orchids.

I would like to note that orchids are not the only flower that are bi-lateral symmetric so it is not safe to say that all bi-laterally symmetric flowers are orchids. Another example would be the flowers of a pea.

I've had a few discussions where people try to say that Cirrhopetalum orchids are not bi-latteraly symmetric:

The thing to point out is that what looks like one flower is actually multiple flowers connecting at the same point. If you then look at each individual flower you will see the symmetry.

I know a lot of that was pretty dry material, but I'll try to liven it up for the next topic.