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Friday, May 22, 2015

This Way to the Restaurant.

Nectar guides © Beatriz Moisset

Nectar Guides


Most flowers want to make it easy for the visitor to find its way around. Thus, in addition to attracting pollinators with their colors and aromas, they guide their visitors in the right direction. This serves two purposes; it facilitates the task of the pollinator and enables the flower to have its pollen deposited where it is most needed.

Have you noticed the streaks of color radiating from the center of many blossoms? These are the nectar guides that tell the visitor: this is the way to the food. Violets and lupines are good examples. The variety of violets is amazing. We can count more than a hundred species and hybrids. Most of them are native, although a few have been introduced from Europe. As a footnote, it is worth mentioning that some violet species are the food plant of fritillary butterflies.

© Beatriz Moisset 

Don’t you find it rather surprising that the humble violet is the state flower of four states? It would be more correct to say violets, plural. Illinois did not attempt to specify which species, even after giving their flower the name of purple violet to distinguish it from yellow violets. New Jersey and Wisconsin chose the Viola sororia and Rhode Island, Viola palmata. Botanists and horticulturists pay attention to these things. However, legislators often ignore such details. This doesn't matter since all violets exemplify the nectar guides vividly.

Illinois: Purple Violet (Viola)
New Jersey: Common Blue Violet (Viola sororia)
Rhode Island: Violet (Viola palmata)
Wisconsin: Common Blue Violet (Viola sororia)


Texas bluebonnet © Jacopo Werther. Wikicommons

A slightly different type of nectar guides is present in bluebonnets (Lupinus). This Texas state flower includes all the species of bluebonnet that grow in that state. The guides become visible only when the flower opens and becomes receptive to pollinators. Bluebonnets belong to the pea family, Fabaceae, which is valuable to ecosystems because it enriches the soil by fixing nitrogen.

Texas: Texas Bluebonnet (Lupinus spp.)



Bull’s Eye


Some flowers use a different way to guide the pollinator to the desired place. It is called bull's eye. The color of the flower's center contrasts with the rest of the blossom. Several state flowers illustrate variations of this theme. Maryland's black-eyed Susan and Oklahoma's Indian blanket are fine examples. So are Florida's tickseed and Kansas' sunflower.


Sunflower © Beatriz Moisset 
Pollination researchers played a trick on visitors to these flowers to test the hypothesis that the bull's eye helped them find their way. They methodically pulled out all the petals of flowers of this type and glued them back in after reversing their position so that the darker part was in the outside. True enough, bees would land on the blossom, walk to the edge and stick their tongues out in search of nectar. They must have been mighty puzzled and annoyed at finding none.


Indian blanket. © Beatriz Moisset 

Some flowers, such as coreopsis, apparently lack this contrast. They appear uniformly yellow to our eyes. But bees see certain colors that escape us. They can see in the range of ultraviolet light, the so-called black light. The flowers, in turn, have a pattern that becomes visible only under this particular kind of light waves. The flower that appears uniformly yellow to us is seen by a bee as having a black center surrounded by a light halo.

Coreopsis. The bull's eye is visible only under ultraviolet light. © Beatriz Moisset 
Maryland, Florida and Kansas have state flowers with bull's eyes, black-eyed Susan, tickseed, and sunflower, respectively. Oklahoma is rather unusual in having not one but three types of flower symbols: the mistletoe as its floral emblem, the Oklahoma rose as its state flower and the Indian blanket, as its state wildflower. The latter has a conspicuous bull's eye.

Maryland: Black-eyed Susan (Rudbeckia hirta)
Florida (Wildflower): Tickseed (Coreopsis)
Kansas: Sunflower (Helianthus annuus)
Oklahoma (Wildflower): Indian Blanket (Gaillardia pulchella)

This article is about one of the many ways in which flowers increase the efficiency of the pollination process. In the next post we'll see examples of another strategy, frugality.



References

Black-eyedSusan under ultraviolet light
Dowden, Anne O. State Flowers. 1978
Cooper, Jason, The Rourke Guide to State Symbols. Flowers. 1942