Not all flowers are what we would consider beautiful. Some are simple and delicate, some are strikingly colorful and included in bouquets, but still others are rather plain, open only at night when we usually can’t see them, or even smell like rotting meat. We have to remember we are not the plants’ primary audience.
Dr. Debra Trock, Senior Collections Manager in Botany at the California Academy of Sciences, discussed the co-evolution of flowering plants and their various animal pollinators during her monthly enrichment talk. Held the third Tuesday evening of each month in one of Chabot’s second-floor classrooms, these free talks from local researchers are open to Chabot staff, volunteers and guests.
Dr. Trock began her talk by clarifying the concept of co-evolution. Evolution happens within populations over time, as natural selection favors the individuals best able to reproduce in any given environment. And co-evolution occurs when two or more species evolve together, each adapting to changes in the other. She also illustrated the basic internal biology of a flower, labeling the various regions of the pistil, the female reproductive structure, and the stamen, the male structure.
Over time, flowers tended to evolve from radial symmetry, with their parts symmetrical in all directions, to bilateral symmetry, with two symmetrical halves separated by a center line. They also tended to move from having a superior ovary located above the other flower parts to a more protected inferior ovary nestled below the petals. Also, flower parts became fused together, rather than free and separated, and started to grow in fixed numbers (i.e. only four petals per flower, no matter how long it has been growing).
Gymnosperms are plants such as pines, redwoods, etc which produce seeds on the surface of scales, leaves, cones or stalks instead of bearing flowers. They are pollinated by wind, which requires a small drop of resin. The resin began to attract animals over time, who then assisted in pollination and formed a symbiotic, mutually beneficial relationship.
The evolution of angiosperms, or flowering plants, carried this relationship still further. Plants began to produce nectaries with food for pollinators, and flowers started to include both male and female parts to increase the chance that pollen grains from the stamen of one flower would find their way to the pistil of another. Angiosperms became highly specialized, taking over many different ecological niches, and the insects and other animals who pollinated them diversified as well.
Botanists and ecologists can look at flowers and form an educated guess as to how they are likely pollinated. Beetle-pollinated flowers have to be strong enough to support the larger insects and tend to have large single fleshy flowers or bunches of small flowers aggregated into a large group called an inflorescence. They are often white or green and sometimes bad-smelling.
Bee-pollinated flowers often have distinct patterns and showy bright petals in all sorts of colors, except red, which bees cannot see. They provide nectar and a landing platform for bees, who have in turn evolved bristles on their legs to carry pollen grains and elongated mouth parts customized for the particular type of flowers they visit. Orchids, which can be pollinated by wasps, have pollen-containing sacs called pollinia and modified petals resembling the body of a female wasp.
Flowers pollinated by butterflies and moths tend to be fragrant, as these insects are drawn in by smell, and are long and tubular to accommodate these creatures’ long tongues. Those attracting butterflies are often bright red or orange, and those attracting moths are usually nocturnal and pale in color. Fly-pollinated flowers often have faint or no color because flies have low or no color vision and a very strong, sometimes noxious, smell.
Another interesting partnership is between the eight-meter tall yucca plant, which has inflorescences, or groups of flowers, that weigh up to 50 pounds, and its tiny moth pollinator. These moths, which can have a wingspan of just 20-25 millimeters, deposit larvae within the plant, who then grow up eating nearly twenty percent of the seeds.
Bird-pollinated plants usually produce flowers that are odorless and red or yellow, since birds respond to color. They have long, large tubes to accommodate a bird’s beak and a good amount of nectar to feed a bird, but not quite enough for a whole meal. This encourages the birds to pollinate multiple flowers. Bat-pollinated plants usually have large, tubular fruity-scented flowers, for bats with long tongues and muzzles.
Some plants also produce fruits as food for animals who eat them and disperse the seeds. Some seeds also need to pass through an animal’s digestive system in order to germinate, a process known as zoochory. Plants such as bloodroot produce protein coverings to encourage animals to eat the seeds. There are a whole other set of mutualistic relationships where certain plants co-evolve to feed specific animals. Some animals also can eat the byproducts of plant photosynthesis and benefit from them, either as food or as chemical defense against their own predators.
Some insects also eat plants, and the plants protect themselves against herbivory in various ways. Grass, for example, has a long tip made of undifferentiated meristem tissue that can regrow easily, so mowing and grazing don’t affect its long-term growth patterns. This evolved in response to many creatures grazing. Other plants form long-term relationships with insects, such as ants. The plants give ants proteins and fats to eat, and the insects protect the plant from predators and competitors.
In closing, Dr. Trock stated that humans, and large animals in general, needed plants more than they needed us. She also suggested that climate change might force a re-calibration of the plant/insect relationship by shifting seasonally determined flowering times and throwing things out of synchronization.
Dr. Debra Trock, Senior Collections Manager in Botany (CAS) – BIO
Debra’s background in biology is broad, having majored in Wildlife Biology/Natural History as an undergraduate at Kansas State University, where she received a B.S. in 1991. She earned an M.S. in 1993 after working with a paleontologist comparing a living intertidal community with a fossil community of organisms, and a PhD in Systematic Botany in 1999.
She spent 3 years working at the Botanical Research Institute of Texas in Fort Worth as Head of Bioinformatics and Collections Management and 3 years as a Visiting Assistant Professor and Curator of the Herbarium at Michigan State University. She has been at the California Academy of Sciences since May of 2005.
Her research focuses on the genus Packera a genus of 67 species of plants in the sunflower family (Asteraceae), which occur across North America, but are particularly abundant in mountainous areas. She is also involved with the Flora of North America project, serving on the Board of Directors for the past 8 years and on the Executive Committee for the past 5 years. She also serves as an author and editor for various parts of that project.
Her primary job at the California Academy of Sciences is to manage the herbarium collection of approximately 2 million specimens. Her team of 30-40 volunteers help prepare 20,000 new specimens each year. The Academy is also in the process of digitizing collection information from specimens, with over 400,000 records in an on-line database.
Debra enjoys teaching and taught night classes at community colleges for many years. She has most recently been involved in helping to teach the biology classes for the docent program at the Academy.