The irises my wife, Elizabeth, cultivates in our yard are coming into full bloom as I write this. Their shapes and colors and fragrances are almost too intricate to describe.
The name iris, meaning rainbow, was given to the group of flowers so-called because of their varied and subtle colors. Some also know them as “fleur-de-lis” (flower-of-Louis) because the crusader Louis VII selected an iris as his family emblem. And many also know them as “blue flags” for the obvious reason that the blue varieties seemingly hold forth their stately blooms like flags in a parade. By any name, the irises we encounter here in the southern mountains are among our most showy and interesting wildflowers.
To my knowledge, five iris species have been reported from the Smokies region: dwarf-crested iris (Iris cristata), slender blue flag (I. prismatica), yellow flag (I. pseudacorus), dwarf iris (I. verna), and southern blue flag (I. virginica). Northern blue flag — the largest of the blue-colored species (I. veriscolor) — grows wild only as far south as Virginia in the mountains.
Three of these species are commonly encountered. Dwarf-crested iris, which grows in rich woodlands, is no doubt the most common. The four-inch high plants literally carpet the ground in places from April into May, and can be observed flowering on into June in the higher elevations. Dwarf iris resembles dwarf- crested iris but is slightly taller, has a less conspicuous crest on its sepals and narrower leaves, and favors dry, rocky woodlands. My favorite species is southern blue flag, which grows about two feet high and displays a yellow blotch at the base of each sepal. It appears in marshes and along stream banks.
The next time you encounter an iris growing in the wild, take time to observe the plant closely. You’ll find that it has devised an ingenious floral architecture that virtually prohibits self-pollination, thereby insuring a more vigorous and robust population.
Bumblebees are the primary iris pollinators. They can land only on the outer tip of the horizontal sepals. The colorful lines, crests, or blotches on the inner part of the sepal are called “nectar guides.” They have the same purpose as the lights on an airplane runway; that is, they guide the insect toward the nectar located at the base of the flower.
To get there, a bumblebee must first push under the upturned female parts. If there is pollen on the insect’s back from another iris, it will be deposited on this stigma and the setting of fruit will occur via cross-fertilization. Once past the female part, a bumblebee must rub its back against the pollen-bearing male part before reaching the nectar source.
After feeding on iris nectar, bumblebees normally slip out of the side of the flower through special openings. But even if the insect exited the way it entered, its back won’t touched the upturned female part because of the way it’s tilted. But the stigma of the next iris it enters from the front will be dusted with the pollen on its back. Any opportunity for self-fertilization is virtually eliminated.
The wildflower colors and shapes and fragrances we seek out and admire for their aesthetic values are in every instance the result of long-term relationships with various pollinators: beetles, flies, bumblebees, hummingbirds, gnats, etc. The old adage that “form follows function” is nowhere more true. It follows that the more closely we observe the specific interrelationships wildflowers have with pollinators, the more fully we can appreciate floral architecture.