It's Not Easy Being Green, Or Is It?

I recently came across a population of one of our more common orchids, Habenaria repens, in a wet ditch in the Orlando area. Known by the common name of 'Water Spider Orchid', plants are notoriously difficult to see even when in full flower, owing to the fact that the plant, along with its minuscule flowers (which are a bit over 1 cm wide), is completely green to yellow-green.

This might cause you to wonder, "How on earth would a completely green flower stand out enough from its background vegetation to be seen by a pollinator?" Just FYI, these flowers are not self-pollinating. It's easy enough to see a flash of pink, red, purple, blue, or buttery yellow against the sea of background vegetation and hone in on the location of a flower, even from a fair distance, but green just blends in with all the other greens that you see. The answer is that it's all a matter of timing.

Walk by the same roadside ditch at night and the flowers will be even less observable by the sense of sight. But even our ridiculously dull sense of smell will pick up a distinct, sweet fragrance wafting over the shallow water. A night flying moth, with a much stronger sense of smell, will be able to find these flowers from miles away, provided that it is not misled by all of our 'artificial moons' (electric lights of various kinds) that interfere with its sense of lunar navigation. Following this stream of sweet odor, these vampires of the Lepidoptera make their way to their quarry. Inserting their probosces into the spur-like nectary that is formed by the back of the lip, they drink sweet nectar from the last few millimeters at the end of the spur. This reward is not, however, offered without its price. The eyes of the insects engage the tips of the pollen-bearing structures (known as pollinia) which are coated with a sticky glue. Thus, when the insect withdraws, its eyes now bear the pollinia to carry them to the next flower. It's a dance between insect and flower that goes largely unobserved, unless you happen to shine a flashlight on a flowering stem at just the right moment.

This strategy of night-scented orchids is actually pretty common in Florida, although not all of them are green-flowered. Some flowers are brilliant white, which might make them more observable in the dim starlight or moonlight that reaches the inner recesses of the forests and swamps where many of these species make their homes. Here is a list of Floridian orchids that are known to be night-scented:

• Dendrophylax lindenii
• Dendrophylax porrectus
• Epidendrum amphistomum
• Epidendrum floridense
• Epidendrum magnoliae
• Epidendrum nocturnum
• Habenaria macroceratitis
• Habenaria odontopetala
• Habenaria quinqueseta
• Habenaria repens
• Tipularia discolor
  

And here is a list of species that are likely night-scented as well, extrapolating from their inconspicuously colored flowers:

• Epidendrum rigidum
• Epidendrum strobiliferum
• Habenaria distans
• Platanthera flava
• Platanthera clavellata

I would be interested to hear about anyone's experience around these species, whether or not they have a night fragrance as well.