Monday, March 9, 2015

What is a Flower? (Part I)

By: H. Wayne Shew, Ph.D. (photo of Dr. Shew teaching)

*in conjunction with Alabama Allergy & Asthma Center

“A rose by any other name…” For most of us the word flower brings to mind something pretty to look at and/or pleasant to smell, and which grows in gardens or in pots on our patios. Flowers are typically thought of around Valentine’s Day, or birthdays, or anniversaries because they are often given as gifts to people you love or care about. They are also associated with funerals for the same reasons; we care about the deceased or his or her family, and want to show that love and concern by sending flowers.

Botanically speaking, the flower is the reproductive structure of plants. It is designed as the place to produce and house seeds until they are ready to be released from the plant to start another generation. Flowers are remarkable plant organs that can differ greatly from one species of plant to another. However, all flowers tend to have certain features in common which function to provide a means for the plant to reproduce itself.

What are the similarities between flowers, and what are some of the differences? Why talk about flowers when your allergy or someone else’s allergy is due to oak pollen or birch pollen and you don’t see anything you would call flowers on these trees? In fact, you might even be thinking, do oak trees have flowers? The short answer is yes, absolutely they do. If a plant produces a fruit, then by definition it also must produce flowers; fruits are the products of flowers. The function of the fruit is to house the seeds and in so doing to help insure that they are protected and get distributed. Seeds are the way that most plants propagate themselves and insure production of the next generation of that plant. Consider oak trees for example. Oaks produce acorns, the fruit of the oak tree, and each acorn contains one seed which can serve to reproduce that oak tree.

All flowers possess one or more of the following structures: stamens (male component of the flower—easy to remember that it is the male part since it has “men” in the name), carpels (female component of the flower—may be called a pistil), petals, and sepals. (See figure below.) The part of most interest to allergy sufferers is the stamen, which consists of a filament and an anther. The anther produces the pollen which is then shed from the flower. The pollen must be transported by some means to another flower, or in some cases to the carpel of the same flower, in order to effect reproduction. The transfer of pollen from one flower to another is called pollination. (Consideration and discussion of pollen will be presented in subsequent blogs.)

Flowers which are associated with allergy symptoms typically do not have showy flowers. In fact, the flowers are often never noticed by most people because they are “inconspicuous,” lacking color and fragrance. For example, think about oaks, trees which produce all of those brown things that fall on the ground or sidewalk in the spring which look like dead worms. Those “worms” are actually a cluster of dead, male flowers attached to one flower stalk. One cluster of these unisexual (male) flowers is called a catkin, a type of inflorescence. Each male flower in this inflorescence has anthers that produce large amounts of pollen. The pollen of each flower when combined with the pollen produced by all of the other flowers in the catkin along with that from all of the catkins on the tree, yields millions and millions of pollen grains which are dispersed into the air. This is why during March and April many of you will suffer from allergic rhinitis. The oak pollen present in the air in large amounts triggers allergic symptoms in many individuals. If you are allergic to oak pollen, “beware the Ides of April.”

To be continued in subsequent blogs….

Note catkins hanging down from limb of this water oak.

H. Wayne Shew, Ph.D.
NAB certified counter
BSC/AAAC Collection Station—Birmingham, Alabama

In conjunction with


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