The Original Mystery Plant

Photo by Robert Malinowski

It's spring! Everything is turning green and yellow. Just about everywhere you look these days, there is a distinct yellow, grainy film settling down on just about every surface, living and non- living. Of course, it is pollen, and it's one of our favorite things to complain about.

Pollen is an important fact of botanical life, and it's vital to the reproduction of all land- based, seed- producing plants. There are also land- based mosses and ferns, but they don't produce pollen.

Pollination is the process of the actual movement of pollen grains into relatively close proximity to the ovules of a plant, and if all goes well, fertilization of the ovules will result. Without pollination there can be no fertilization, and without fertilization, seeds are not formed, and thus no reproduction. Very clearly, successful pollination is a requirement for most plants grown in cultivation from which we harvest fruits.

Flowering plants as well as conifers produce pollen, in the form of tiny grains. Pollen comes from a Latin word meaning flour. Each grain is actually a tiny individual plant, and contains one or several cells within, some of which are ultimately capable of acting as sperm cells. The grains themselves tend to be characteristic, and recognizable, within various plant groups, and it is usually easy to differentiate such groups, based on the appearance of a pollen grain under a microscope.

Aside from a dirty car, pollen may indeed be a serious matter to cope with, as certain plant species produce pollen that is highly allergenic.

For humans, allergic responses are extremely variable from one person to another, but these allergies are usually caused by a physiologic response to proteins in the wall of the pollen grain. Some plant species are rather improperly accused of producing allergies, the worst culprits are, as a rule, those species that are wind- pollinated, rather than those whose flowers attract insect visitors for this purpose.

Goldenrods and asters in the fall are commonly accused as culprits, but actually their pollen is not particularly problematic. On the other hand, the wind- pollinated ragweeds, oaks, and hickories may be guiltier.

The pollen pictured here is that of a very common pine, viewed with about 20X magnification. Each grain is about 3/1000's of an inch long. The main body of the grain bears a couple of bulbous, rounded wings, and thus an intact grain somewhat resembles a Mickey-Mouse face.

The very sight of a cloud of yellow pollen falling from trees in the spring can send some of us running for the antihistamines. Our complaints should be tempered with the knowledge of the importance of pollen in the biology of the plants around us and the realization that eventually it will largely go away.

On the other hand, the folks at the car washes aren't complaining too much.

Answer to this week's mystery plant

[Answer: "Loblolly pine," Pinus taeda]

Dr. John Nelson is the curator of the USC Herbarium.

To learn more about the Herbarium, call 777-8196. The

department also offers free plant identification.

www.herbarium.org