Trees in Love: The Secret Life of Tree Flowers
Spring 2000
By Christina Krueger
For many of us, the long, cold winter often seems eternal while spring is just a fleeting moment. Spring brings the awakened activity of hibernating animals. But nothing signifies the arrival of spring better than the blossoming flowers on trees. What's so special about flowers anyway? We see them everyday in our homes, offices and gardens. They are present for all the significant events in our lives, from weddings to funerals. Flowers are powerful symbols of the human spirit, from the rose of romantic love to the sacred lotus of Buddha. They are a source of inspiration for artists, poets and naturalists of all ages and backgrounds. It is the flower that develops into the seeds and fruit that we readily consume.
Flowering plants, or Angiosperms, evolved more than 140 million years ago and have become the most successful and diverse group of plants the world has ever seen. Within a bud, the petals and sepals form the body of the flower which protects both the male and female reproductive organs . The male organ, or "stamen," produces pollen which contains sperm. The plant's female organ, or "pistil," houses the egg-containing ovary. The cherry blossom is the text-book example of the "perfect flower," where the petals, sepals, pistils and stamen are all clearly visible. The goal is to unite the pollen of a flower with the ovary of a flower of the same species. Once a flower is pollinated, the mature ovary will develop into fruit. The mature fruit, contains one to many seeds, each with a developing embryo inside. These embryos will eventually become the flower-producing trees of the future.
In the case of the tuliptree, magnolias and maples, both the male and female organs are on the same flower. In other groups, such as birches, oaks and hickories, the male and female organs are on different flowers while on the same tree. Still another variation exists in the willow and poplar species, including aspens and cottonwoods, where the male and female flowers are on separate trees altogether. Though the reproductive organs are the essential parts of the flower, they are not the most showy. It is the petals, or modified leaves, that serve to attract insects or birds. Over 60% of all flowering plants are pollinated by insects. A number of flowering trees, however, are pollinated by wind. The early spring winds are ideal for blowing pollen from tree to tree, and into our nostrils! These tree flowers often open before the leaves emerge and are found on the tops of the tree. It makes perfect sense, then, that many of the tallest trees are pollinated by wind, such as the red oak.
The flowers we love are usually the big, conspicuous ones. You can bet they are almost always pollinated by insects. These flowers produce nectar, which attracts insects. In their quest for nectar, these insects unwittingly transfer the pollen from flower to flower. Nectar is of no use to the plant and making it is costly, but that is the price of reproductive success. Bright, colorful flowers are eye-catching to insects (and to humans). Some flowers also emit odors that serve as insect beacons; some are sweet; some, like sassafras, are foul-smelling (like rotting meat) to attract carrion-craving flies. Many flowers have additional clues to guide insects. Some have petals with alternating colors or dark spots in the flower's center to steer the insects toward the pollen and nectar source.
Nature has conjured up some remarkable ways of aiding reproduction through the interplay of plants and animals, and the insouciance of air in motion. And flamboyant treeflowers rank with the best. So as our smiles grow wider as days grow warmer, take a moment to observe the electricity of life around us. For those who dread allergies brought on by pollen, be comforted that Spring is but a fleeting moment.