labellum

3

Whew! After that long winter holiday hiatus, we’re going to explore the Orchids. This family of plants (Orchidaceae) has captivated the imaginations and minds of generations of people. There are tens of thousands of species in this family, making it possibly the largest plant families in the plant kingdom. One of the primary reasons for our love affair with orchids, and also explaining the vast number of species in this family, is the highly evolved and specialized flowers in this family.

The images presented today are of an orchid that I managed to bring to flowering in my house. I’m actually quite terrible with growing orchids, so I was super excited to see this flowering. I need to look up the name of the species, but let me know if you know if off hand.

Anyway, we need to get oriented properly with this flower. For the most part orchid flowers are twisted 180 degrees at the stalk so the top is actually the bottom. This condition is called resupinate.

Although they look a bit strange, it is still possible to distinguish the floral parts. The outermost layer of the flower consists of three large sepals. The next layer is a set of three petals. Two of them are small and narrow in this orchid, but one of them is modified into a highly complex structure called the labellum. This highly modified petal is the key to most orchid flowers. Many have evolved into large landing platforms that attract specific pollinators. Ophrys, for example, is known for its modified labellum that mimics a female bee to such an extent that male bees attempt to mate with them, this is known as pseudocopulation. These labella can be finely tuned to specific pollinators and have assisted orchids in speciating incredibly rapidly.

In the very centre of the flower, the pistil and the anthers are fused into a structure called a column. The anther cap (labelled) hides big balls of pollen called pollinia. The pollinia are dispersed as one unit, so orchid flowers only get one chance to pollinate another flower. Attached to the pollinia are often little stalks called caudicles and little glue patches called viscidia. In many species, the viscidia stick onto the head of pollinators. As the pollinator flies away, the caudicle dries up and becomes brittle, which then breaks off into the stigma of the next flower visited.

Anyway, there is so much more to learn about orchids, and a quick wiki search can give you some great background. However, if you’ve got any specific questions please feel free to ask me.