Tuesday, July 26, 2022

Small Green Wood Orchids

A pair of Small Green Wood Orchids (Platanthera clavellata) in perfect flower on a mossy tree base. The larger one towered to about 6-8 inches in height. Not much is known about its pollination biology, but moths are almost certainly the pollinators. These plants are in a west-central Ohio woodland, about 45 minutes west of Columbus. I made these images yesterday afternoon.

This little orchid is scattered in small populations, and rather rare from my experience. But it is certainly overlooked. Platanthera clavellata flowers in shady haunts in the heat of mid-summer, and such habitats probably are not as well botanized as they should be at that season. Mosquitoes help to drive botanists from such sites, along with the heat and humidity.

A close-up of the inflorescence, which is heavily laden with tiny flowers in perfect condition. Note the luminescent whitish cast to the flowers, and long tubular nectar spurs. Both features select for moths. But which moths? Well, the mystery thickens. The great botanist Asa Gray was the first person to figure out that P. clavellata is at least partially self-pollinating. Pollen germinates within the pollinia (pollen sacs) and then grows downward into the stigma (female receptacle).

That said, this orchid's flowers are tailor-made for moth pollination. The luminescent greenish-white color would be highly visible in darkness, and those very long nectar spurs (the slender tubes trailing from the flowers) are typical of orchids that favor pollination by moths with long probosci. Furthermore, there is at least one known case of hybridization. The great orchidologist Fred Case, at the University of Michigan, found a hybrid between this species and White-fringed Bog Orchid (Platanthera blephariglottis). Thus, pollinating insects must sometimes visit, and they would almost certainly be moths.

As evidence of the luminosity of the flowers, I shot these images on a bright overcast day, but the orchids were in full shade. Exposing at neutral on the meter rendered completely blown out - overexposed - images. It was necessary to underexpose by about two full stops to get a correct exposure. It's almost as if the flowers are plugged into an outlet and glowing.

If time allows, I hope to get back to these plants around dusk, and watch them into nightfall, to see if moths do visit. And if so, try to capture them on pixels and hopefully identify them. 

No comments: