“Midway on our life’s journey, I found myself/In dark woods…lost.” The tangle of old logging roads and abandoned trails north of Kings’ Farm turned me around this morning, adding a half hour or more to my trek. Virgil did not appear. He never does. But, by getting lost, I did stumble on some great little plants: about a dozen cranefly orchids in the leaf litter on the side of an old trail.
Cranefly orchid, Tipularia discolor
Unlike most other woodland plants, cranefly orchids grow their leaves in the fall, keep them through the winter, then let them die in spring. Later, in midsummer, the spindly flower stalk emerges without any leaves, using belowground food stores to power its growth. So, this orchid’s life is powered by the weak winter sun.
The green, upper surface of the leaves is pleated, giving it a crinkled appearance. More striking, though, is the purple underside of the leaf. Sometimes this purple bleeds into the upper surface, especially later in winter.
Underside of cranefly orchid leaf
This purple pigment is there to protect the leaf on cold days. When the photosynthetic machinery inside the leaf is iced-up, it can no longer absorb the energized electrons that sunlight knocks free from chlorophyll and other green pigments. The purple pigment soaks up these crazed electrons, keeping the leaf’s innards safe.
Lovely. Does it bloom?
In midsummer it puts up a a long stalk with rows of small flowers. Very hard to find these flower stalks — inconspicuous.
The flowers are worth looking at through a hand lens — as pretty, I think, as any florist’s orchid, though a bit on the subtle side. They are quite common in our second- and third-growth Virginia piedmont woods. I also find a lot of rattlesnake plantains, another frequently seen native orchid with an interesting downy, crosshatched leaf. BTW, I didn’t know about the purpose of the purple pigmentation on the underside of the cranefly orchid’s leaf. Pretty cool.
I’ve been doing library research on the function of anthocyanin pigments and have been puzzled about the purple undersurface of the cranefly orchid. According to what I’ve read the anthocyanin is found in the vacuole. Since the electrons are being kicked out in the chloroplasts how do they get neutralized by the pigment in the vacuole. Another thing puzzles me. The undersurface of the Tipularia leaf is purple. This suggests that the purple pigment is in the mesophyll and/or lower epidermis. Again, this makes it far away from the palisade layer where most of the photosynthesis is taking place. Can you shed any light on these problems?
BTW: Last year I read and greatly enjoyed your book. I didn’t realize you had a blog until a student pointed me to this post — we had seen new cranefly leaves on a walk in our local woods and I told her that I didn’t understand why the lower surface had the pigment.
I’m also adding your blog to my feed.
Thank you, Dale. And good questions. My statement was based on physiology of other overwintering leaves, so you’re absolutely right that purple in cranefly orchids might have some other function. There is not, as far as I can tell, much know. The one paper that has examined photosynthesis (http://www.academicroom.com/article/photosynthesis-and-carbon-allocation-tipularia-discolor-orchidaceae-wintergreen-understory-herb) did not have purple pigments as its focus. I’ll ask around and see what I can find.