In the Garden:
Coastal and Tropical South
Banana shrub flowers curve in on themselves to protect the pollen, but seldom appear in June in New Orleans.
The natural world puts on an unparalleled show in its shameless efforts to continue its existence. Since success depends on timing, what does it mean when plants bloom out of sync with their pollinators?
Plants know their reason for being, which is to reproduce. That usually means growing a viable flower and getting it pollinated. Attracting pollinators may not seem exciting, but flowers go to great lengths in the courtship dance. We get to see them every day in our gardens, but there is more going on than meets the eye. Flowers can be male, female, or complete, meaning they have both male and female structures in one bloom. If a species cannot pollinate itself, insects are often the path to union. Even if a plant can self-pollinate, like many fruits, its genetic makeup benefits from cross-pollination and often produces more fruit, too.
Here's how it works: Pollen is produced on the anther, which is often a landing pad. It must travel onto the stigma and through the pistil tube to unite with the ovary and fertilize it. Every flower's job is to make this happen. Fragrance and color start the seduction, but it is the flower's structure itself that seals the complicated deal. Insect pollinators seek nectar and will crawl across almost any pollen-covered surface to get it. As they move about in the flower and from plant to plant, the pollen moves with them to its ultimate destination.
The flowers of the temperate zone live an orderly life with plentiful pollinators. Many plants in the Compositae family, for example, have basic daisy shaped flowers, with all their parts arranged in fairly predictable ways. Look closely at a zinnia or gazania to see how an insect can land, partake of nectar, and in the process, move the pollen.
Many tropical plants, particularly those from rainforest ecosystems, must develop much more complicated ways to entice the insects. Where there are more flowers than pollinators, each ant or beetle has to do at least double duty, and the flowers evolve to insure the pollen they receive is compatible. For example, the corkscrew flower (Vigna caracalla) has an elaborately coiled petal structure meant to direct the pollen-laden ant to the left, presumably to avoid such contamination. It is a legume, a tropical bean, but its flower looks more like an orchid. Equally spectacular are the tubular flowers that lure tiny insects to take a precarious journey for a chance at nectar deep in the flower's heart. They evolved to deter predators and insure a safe, if convoluted, passage for the pollinator. It's a tight fit into a honeysuckle, and angel trumpet must look like the Empire State Building to that tiny, yet essential, visitor.
Wildly colorful bracts do more than just attract the wandering insect. They protect the precious true flowers until the insects can reach them. The tiny white flower inside the bracts of bougainvillea and the small yellow cluster at the center of poinsettia have this natural protection against rapid aging that could prevent pollination.
Timing is everything when it comes to pollination and seed production. The insect must be in search of nectar when the pollen is viable and the flower is receptive. All of this amazing activity that produces the incredible flowers we enjoy is directed towards reproduction., But lately many plants seem to be flowering more often outside of what in the past was their natural bloom period. Flower calendars around the world have noted that many species in every climate zone are blooming a month or more ahead of the expected cycle. Many insect life cycles have evolved to be in sync with particular flowers' bloom times, such as the Gulf fritillary that uses passionflower to host caterpillars and provide nectar to adult butterflies.
There are occasional reports of poor pollination that might be attributed to this phenomenon and concerns about other odd flowering habits. Tulip trees in south Louisiana always bloom in early spring, sometimes early enough to suffer frozen flower. For the past several years, however, the trees have bloomed again in September for no apparent reason. The same is true with common wisteria, which has rebloomed without the cold conditions that have been thought to control the timing of flower production. Theories abound, but no one knows exactly why this happens or what the implications could be. We keep track, but have little or no control over when flowers bloom and insects hatch. That is as it should be in the mysterious world of nature, despite how frustrating it can be. Gardeners should rely on history and stay optimistic, in the hope that the flowers and insects will continue to evolve together and reward us with awesome flowers.
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