Flower colors

musings on the palette of summer

Just before the summer solstice, a little group of friends walked out onto Cowee Meadow. Although it was raining in town, out there, the sun was shining. The meadows were a blaze of color: pink shooting stars, yellow buttercups, and blue lupines covered acres with floral glory. While those species were dominant in the meadows, we counted over sixty species of flowers on our walk (not counting grasses and sedges). We did include the irises, which were just starting to bloom; in another week or two, irises will be the main show.

Among all the blue lupines were three or four individuals with pink flowers, and we’ve sometimes seen very pale shooting stars. On the upper beach, there’s the usual blue-flowered oysterplant, with a few white-flowered individuals—and even one plant that apparently made both blue and white flowers. Rare white-flowered geraniums and beach peas are also reported among the usual purplish ones, and some chocolate lilies have yellow (instead of brown) flowers. That made us wonder about the fate of these mutants—do they get visited by insects or are they reproductive failures?

While cogitating about flower color, we also commented that white flowers seem to characterize more of our native, local flowering species than any other color, although many of those white flowers are small and inconspicuous. There’s a fair number of species with blue/purple, yellow, or pink flowers, but red, orange, and green flowers are rare. However, white may not predominate in our alpine zones–It might be interesting to compare the frequency distribution of floral colors in different habitats and contemplate possible relationships with the available pollinator fauna (or other factors).

A common white flower on the Cowee Meadow trail is dwarf dogwood (bunchberry). It’s so common and familiar that it often escapes notice! That ‘flower’ is really an inflorescence composed of four whitish bracts surrounding a tight central cluster of actual flowers. There were many other things to look at on that hike, so I didn’t take time to inspect those dogwood inflorescences closely.

Photo by Kerry Howard

However, a few days earlier, I had done so on the Eaglecrest Lower Loop—higher in elevation, so the dogwoods were then less advanced and I could observe the seasonal progression of floral development. Some dogwood inflorescences were just opening and the bracts were small and green; the floral buds in the center were dark and tightly closed over the male and female parts inside. On more advanced inflorescences, the bracts were bigger and greenish-white, while the floral buds were still dark and closed. Then the bracts get bigger and whiter, and by the time they are fully mature, the floral buds are starting to open, exposing the sex organs to visiting insects. The flowers ultimately can open by themselves, but studies have shown than an insect visit can trigger floral opening and an explosive release of pollen. In either case, stamens catapult pollen vertically for several centimeters at very high speed, onto an insect or into the breezes. The pollen grains are not sticky, so high-speed release is thought to be necessary for adhering the pollen to an insect. Whether by wind or by insect transport, pollination is only successful when pollen arrives from a different dogwood individual, because this species is self-incompatible. After pollen is ejected, the pollen-capturing surface of the stigma increases, ready to receive incoming pollen. However, fruit-set generally seems to be low.

Another white-flowered plant was blooming profusely in the meadow along the Lower Loop trail: three-leaf goldthread.  This flower looks nothing like the flower of the related fern-leaf goldthread that mostly grows in the forest. The flower is comprised of several white sepals surrounding the sex organs and five (sometimes six) tiny golden trumpets that are modified petals offering nectar to visiting insects. Although I saw no insects visiting a group of open flowers, I watched a small fly working assiduously for several minutes, trying to gain entry into an almost-open bud.

There must be good stories behind the evolution of flower colors and shapes; I wish I knew them!

Potluck

a selection of summer delicacies

You never know what might be offered at a potluck supper, where you browse over a miscellaneous collection of dishes. This essay is a bit like that—an assortment of unrelated but potentially interesting observations and information.

Last week I mentioned the great abundance of mosquitoes in June in the Interior. Mosquitoes can surely be a major nuisance and in some regions of the world they carry diseases and parasites. But is there another side to this coin?? What good are mosquitoes?

Mosquitos are good bird food. Swallows and swifts catch them on the wing. Certain warblers and flycatchers dart out from a perch to catch them as they fly by. I’d bet that the female hummingbird swooping back and forth in my front yard catches some, too. Mosquito larvae are aquatic and provide good prey for small fish and for larger invertebrates that are also prey for fish. Dragonflies and damselflies feast on them.

Mosquitoes are more than unwilling prey, however; they are the principal pollinators of a diminutive-flowered plant called the small bog orchid. In Alaska, males and females of several species of mosquito are known to visit these orchid flowers and carry pollen from on flower to another (other insect visitors include small moths and flies, but their role in pollination is undocumented). As the mosquitoes poke into a flower, globs of pollen are slapped onto their eyes, where they stick until the mosquito goes to another flower, which is arranged in a way to pull off the pollen, leading to seed development. There may well be other kinds of small flowers that are pollinated by mosquitoes: male mosquitoes commonly live on nectar from flowers and even the blood-sucking females do to in some cases. Some of these visitations might achieve pollen transfer, but sometimes the mosquito might be just a nectar thief.

Flower color is one of the cues used by flower-visiting animals. Color helps identify the species, sometimes the age of the flower, and in some cases, whether or not it has already been visited by a pollinator. Usually, all the flowers of a particular species are the same color, or nearly so. But we see exceptions. For example, almost all of the chocolate lilies we see have brownish flowers, but very rarely we see one with yellowish flowers. Wild lupines normally have blue to purple flowers, but in rare cases we find one with pink flowers. Occasionally, we’ve found white-flowered individuals of fireweed, northern geranium, shooting star, and bluebells (whose flowers are normally pink or blue). These very unusual flower colors are presumably the result of genetic mutations.

yellow-chocolate-lilies-Denise.jpg
Photo by Denise Carroll

These mutants don’t seem to spread and become more common in their respective populations. But why? Do pollinators discriminate against those oddballs, leaving them unvisited, unpollinated, and without offspring? Or, maybe the (presumed) gene that controls flower color also controls something else in the plant’s life, something that interferes with some aspect of normal function. Multiple effects of single genes are common. As usual, a simple observation leads to more questions.

Bumble bees are very important pollinators of many kinds of flowers. They are the principal pollinators of monkshood, lupine, blueberries, iris, louseworts, and beach pea, which have flowers that must be manipulated in a certain way in order to achieve pollination. But the bees also join with a variety of other critters to pollinate roses, salmonberry, thimbleberry, goldenrod, and columbine (to mention just a few).

However, all across North America, from California to the east coast, populations of some bumblebee species have become very rare or even disappeared entirely. Because I have a very unscientific impression that I see fewer bumblebees on our wildflowers in the last two years than previously, I wondered if our bees may also have crashed. I asked the UAF expert, who said that a study currently underway in Denali is designed to detect major changes in bumblebee populations there, but as so often happens, these seem to be no scientific data for Southeast. We can hope that our bumblebees are in good shape, because so many of our wildflowers depend on them.

Finally, and just for fun (?dessert at a potluck?): One day I walked through the Eagle Beach day-use area after a stroll on the beach. I spotted a big black bird sitting on a rock and holding a chunk of something red and drippy in its bill. Through binoculars, I saw that the raven held a succulent piece of watermelon. Just beyond the rock was a picnic table with several plastic containers, temporarily abandoned by a human family that was playing out on the intertidal sand flats. At least two of those containers had the lids removed (?by the raven?) and one of them still held a chunk of melon. That family was in for a surprise when they came back to their table!