Pollination of Platanthera psycodes at Mt. Mitchell State Park, North Carolina — 2015-06-28

This blog entry is intended for the orchid nerds in our midst and for anyone else who is interested in orchid pollination…

I struggled a bit with how to present this topic in my blog. My last visit to Mt. Mitchell State Park in the North Carolina mountains provided me with the opportunity to witness the pollination process of Platanthera psycodes or Small Purple Fringed orchid.

Small Purple Fringed orchid

The Pollinator:

The pollinator I witnessed doing its “thing” with the flowers was an Epargyreus clarus or Silver-spotted Skipper. I found this link which does a much better job of describing the Silver-spotted Skipper than I ever could.

A Skipper is an insect of the family Hesperiidae. They are named after their quick, darting flight habits. More than 3500 species of Skippers are recognized, and they occur worldwide, but with the greatest diversity in the Neotropical regions of Central and South America. Skippers are considered an intermediate form between butterflies and moths.

The Skipper, when not engaged in its darting, erratic flight, typically holds its short wings much like a butterfly in a near vertical position above its moth-like body. It may hold its forward and hind wings at slightly different angles. It has antenna that terminate in knobs that often have fine hook-like extensions. This antenna pattern help distinguish a Skipper from a butterfly, which has a club-like appendage at the ends of the antennae, or a moth, which has feathered or pectinate (comb-shaped) antennae. Skippers come in a broad range of colors and patterns, sometimes with considerable variation among individuals within a species.

The Orchid:

Platanthera psycodes or Small Purple Fringed orchid has a distribution that extends from northern Georgia, northward to the eastern provinces of Canada, and westward to the Mississippi River. At Mt. Mitchell State Park in North Carolina, it is usually in full bloom during the last week in June. It can be found in profusion along the access road leading from the Blue Ridge Parkway to the summit of the mountain. Mt. Mitchell is the tallest point in eastern North America, with an altitude of 6,683 feet (2,037 metes). This altitude provides a climate that more closely resembles that of more northerly regions, allowing the orchid to grow much farther south.

The Small Purple Fringed orchid may grow as tall as 2 to 3 feet (60 to 90 cm), but if growing in full sunlight, it is usually 12 to 15 inches (30 to 40 cm) tall. The inflorescence may have up to 100 or more half-inch wide (1.2 cm) flowers. The color of the flowers varies widely, from white to pink to magenta-purple. There are usually 6 to 8 glossy green, lanceolate-shaped leaves which are larger toward the base of the stem:

The flower has two petals, three sepals, and an enlarged lip. The lip is divided into three lobes, each heavily fringed along the edges. The petals may be lightly fringed and are usually raised upright. The lateral sepals may be slightly or acutely reflexed or bent backward. The nectary opening is just above the base of the lip, and is barbell-shaped. This species is often confused with a similar one, Platanthera grandiflora or Large Purple Fringed orchid. The tell-tale difference is the shape of the nectary opening: barbell-shaped for Small Purple Fringed orchid and round for Large Purple Fringed orchid. My experience shows that the size of the flower is not definitive to the identification:

Small Purple Fringed orchid – barbell-shaped nectary opening

Large Purple Fringed orchid – round nectary opening

Now that you have the necessary background, it’s time to discuss the pollination process. First, we need to look at the “business” parts of the orchid flower:

The main parts of the flower dealing with reproduction are the pollinium (pl. pollinia) which is the male part and the stigma which is the receptive female part. For orchids, unlike most other plants, these parts are found on a unique structure called the column.

Each pollinium has a sticky pad attached to its exposed end. This sticky pad will adhere to anything that touches it. The pads are oriented according to what type of pollinator it has evolved to attract. Some Platanthera orchid species have evolved to attract large butterflies and have their sticky pads oriented toward the front, causing them to attach to the head or eyes of these large insects. Platanthera psycodes or Small Purple Fringed orchid has its sticky pads oriented so that they are facing the nectary opening, allowing them to stick to the proboscis of the pollinator rather than the eyes. When they are pulled from their protective casing, they spring outward so that they will be in position to contact the stigma when the pollinator visits the next flower. In the above color image of the two orchid flowers, you can see that there is a suture on the enclosing protective casing, allowing the pollinium to be removed with only a slight tug.

Orchid pollen, especially where Platanthera species are concerned, is coherent and of a waxy nature, so that even when the pollinium is removed, the pollen grains do not instantly fall apart, but they remain more or less intact until brushed up against the exceedingly sticky surface of the stigma. At this point, fertilization takes place. It’s that simple.

The interesting part for me is to witness the pollinator perform the act of pollination. Yes, I suppose I’m a voyeur of sorts, but this does give me a thrill! On my most recent visit to the orchids at Mt. Mitchell, I was privileged to witness one Silver-spotted Skipper visit almost every flower on four, neighboring orchid inflorescences. It would work its way from the bottom of the inflorescence to the top, circling the inflorescence in a spiraling pattern until it reached the upper-most open flowers. Then it would move to the next inflorescence and repeat the process. The pollinia were quite “ripe” so that they began to fall apart as the Skipper went about its business of sucking the nectar from the orchid’s nectary. The Skipper’s erratic, jerky movements ensured that at least some of the pollen grains would adhere to the flower’s stigma.

Several years ago, I made a few images of a Silver-spotted Skipper visiting one particular Small Purple Fringed orchid plant. The pollinia remained quite intact as it flitted from flower to flower. I have no hypothesis for this observation except that the pollinia may not have been as ripe as they could have been. Here are a couple of images of that Skipper with a cluster of pollinia attached to its proboscis at the point of contact as it was siphoning nectar from the nectary:

However, on my most recent visit, the pollinia which were stuck to the Skipper’s proboscis were quite crumbly so that they began to disintegrate as they were jammed against the flower’s stigma as the Skipper forced its proboscis into the nectary opening. Here are a few images that I captured as the Skipper proceeded around the orchid’s inflorescence:

I never fail to be amazed at this prime example of how orchids and their pollinators have evolved in unison so that it is a win-win proposition for both of them. If climate change becomes extreme, either the orchid will bloom or the pollinator will emerge too early or too late for this wonderful process to occur. Climate change is happening at such an accelerated rate that neither the orchid nor its pollinator will have time enough to modify its life cycle so that they keep this matched pairing that has evolved over millennia.

This writer is not an expert nor does he claim to be on such matters as climate change or pollination. I am a keen observer, though, and I hope that my observations have given you, the reader, some food for thought. Natural processes are sometimes so intricate and complex that there are portions of them that we will never understand. For me, understanding these processes is something I will strive for, and being able to capture their images only a part of the total experience.

–Jim