Plant Pollinators in Action
by Tamara Blett
Plants don’t have on-line dating options for attracting the opposite sex, so they’ve evolved a wild and diverse bunch of strategies for ensuring the next generation of plants. Most plants reproduce by attracting pollinators to their flowers, with unique shapes, smells and colors to guide or tempt them into landing and exploring in just the right place to help bring together the pollen (from the male part of the plant), with the ovule (the female part of the plant). The pollinators benefit by getting a reward of food (nectar or pollen) or place to lay their eggs, and the plants benefit by producing fertilized seeds or fruit to continue their life-cycle into the future.
Here at the San Luis Obispo Botanical Garden we have some fascinating examples of the tricks and strategies plants have evolved to propagate themselves with the help of birds and insects. Flower position is the first one; horizontal flowers tend to attract birds, and flowers that face upward often attract butterflies. One of our favorite butterfly attractors here at the Garden is the common yarrow (Achillea millefolium), which has white flowers in flat clusters. Color is crucial; birds notice red flowers more easily than other colors, while honey bees are color blind to red, but can see purple, yellow and white flowers. Some attractive flowering plants that birds love to visit here, are the hummingbird flower (Epilobium canum) and the island bush snapdragon (Gambelia speciosa).
Plants also release scents to draw in pollinators; sweet smells to attract bees, strong smells to bring in moths, and fruity smells to tempt beetles. The spice bush (Calycanthus occidentalis) near the entrance to the Garden has reddish flowers which are pollinated by a 3mm long beetle. The plant lures the beetle with a strong odor, but once the insect enters the flowers it is trapped by stiff downward pointing bristles and it has been fooled, no nectar is there! The beetle may remain stuck in the flower for up to two days, until the flower releases enough pollen to thoroughly dust the body of the insect. At that point the flower’s petals open wide and the pollen-carrying beetle is released.
Plants may also help the pollinators find the payoff of nectar, by showing them where to land on the flower and giving them directions to the good stuff. “Nectar guides” are lines or patterns on the flower petals that say to an insect “follow me to your nectar reward!” Research has shown that having nectar guides can be beneficial to the plant as well, as the pattern guides the pollinator on a route which is most likely to result in coating the insect with pollen, resulting in greater chances for fertilization of other plants. Peruvian lilies (Alstromeria hybrid) are beautiful, large, pink and yellow flowers that grow in our botanical gardens. If you look closely at the petals, you will notice brown spots and lines which serve as nectar guides for bees on this species.
The Garden Shop has a wide selection of pollinator friendly plants available for sale, so stop by and pick some up for your own home’s landscaping, or come and stroll the paths of the botanical gardens to see plant flirts in action!