"What on Earth?"
Article and photos by Ray Barbehenn
Orchids are renowned around the world for their beautiful flowers. There are over 25,000 species of them, mainly in tropical areas, but over 60 species grow in our area. However, many of our species are hard to find, and you might not realize that some of them are orchids! It also takes some luck to find them while they are in bloom.
A Showy Orchid (left photo) had a gorgeous nine-inch-tall flower spike on April 30. It was blooming in Duke Hollow (northern Virginia along the AT). If you were scouring the woods for morels, there was a good chance you would see this species. The Spotted Coralroot Orchid (right photo) was also blooming in the same area at this time. However, this was only the second one that I have ever seen. It had no leaves – just foot-tall flower stalks! The lower flowers on their stalks were oldest (blooming first), while the top flower buds were just starting to open. Note the white lower petals that popped open on the flowers of both species. These petals are spotted on the Spotted Coralroot. The upper two petals and three sepals (the outer covers of the flower buds) form a hood-like structure in both species. Orchids have very complicated flowers, and some of the oddities of these plants are described below.
How do Coralroot Orchids grow flower stalks without having green leaves?
A. They use stored energy (starch) from their roots.
B. They parasitize fungi to get the needed nutrition.
C. They parasitize tree roots to get the needed nutrition.
D. They had leaves but they died back.
The answer is at the bottom of the page!
Fun Facts and Musings
Let's get past gawking at the beauty of the orchids' flowers, even if only briefly. Orchids are remarkably different from most other plants in several major ways, including the way their flowers work, the tiny size of their seeds, and their early growth.
The complexity of orchid flowers makes one wonder how they ever manage to get pollinated. They are unlike the flowers of most plants, which produce an abundance of powdery pollen. The pollen of most flowers gets dusted on the insects or birds that visit them, and is then brushed onto other flowers when the pollinators visit them. So, where is the powdery pollen in orchids? There is none. Instead, orchid flowers put all of their pollen into a small number of tiny balloon-shaped packets. And, these packets are hidden under a covering that a pollinator must bump open to expose them. If all goes well for the orchid, a pollinator will get some of the sticky pollen packets glued to it before it leaves to visit another orchid flower. Successful pollination only occurs if a pollen packet gets pulled off the pollinator by the even stickier surface on the female part of another orchid flower. The whole process seems as unlikely to work as an odd Rube Goldberg contraption. Orchid flowers may need to wait for weeks or months for pollination to occur, which probably explains why home-grown orchids often hold their blooms for so long.
Pollinated orchid flowers produce seed pods that contain the tiniest seeds of any plant – "dust seeds." In different orchid species, these can range anywhere from microscopic (0.05 mm) to the size of a pinhead (1.5 mm). A pod with microscopic dust seeds could easily release a million seeds! However, they are only able to form such an impressive number of lightweight seeds by leaving out any nutritional reserves for the baby plants! There is no mass of starch (the stored energy that we appreciate for our own nutrition from seeds like corn and rice).
Orchid dust seeds are blown far and wide by the wind, but they have a very small chance of survival. A one-in-a-million chance might not be far from the correct odds. Because an orchid seed contains no nutrition for it to grow, it must land where certain fungi are present that can rescue it. In other words, orchids produce seeds that are helpless to germinate and grow on their own; they need fungal rootlets ("mycelia") to share some of their sugar and other nutrients with them. Why would a fungus want to do that?
Such a cozy interaction may seem strange, but it is abundantly common in nature for fungi to associate with plants in this way; about 80 percent of plant species are engaged in these interactions! What is strange is that the orchid does not readily return the favor, as plants usually do. For two to four years, the orchid grows underground as a parasite of the fungus. The orchid spends this time accumulating starch in its root (similar to a ginger root). At this point, most soil-living orchids send up their first leaves and photosynthesize at least part of their own sugars. They can eventually become self-sufficient, and finally share some of their sugars with the fungi. Perhaps 99% of orchid species grow up this way, though they might still get nutritional help from fungi, especially if they live in a shady area. The Coralroot Orchid is example of the 1% of orchid species that remain parasitic their entire lives. Their reddish stems and flowers may help attract pollinators, but this color also indicates that they lack chlorophyll (green pigments) for photosynthesis.
It is not surprising that many of our orchid species are rare and endangered. They have complex life cycles, difficulties getting pollinated, and more difficulties getting their seedlings established. Those that are doing relatively well, such as the Showy Orchid, are worth a walk in the woods.
Answer: A, B, or C! Here's why: Coralroot Orchids grow a stalk of flowers using the starch stored in their thick coral-colored root (Answer A). But, Coralroot Orchids have no leaves (ever), meaning that the starch in their root was made from the sugars that they absorbed from a fungus's rootlets (Answer B). However, the fungus got this sugar from a tree's roots. Therefore, the orchid's early nutrition ultimately came from parasitizing a tree's roots (Answer C). Yes – orchids are very beautiful, and very odd.
Send your photos and ideas for topics to Ray at rvb@umich.edu.
