Treebeard's Stumper Answer
Blowing in the Wind
We all learn that flowers attract insects to carry their pollen from plant to plant. But my sinuses tell me otherwise. I've had hay fever lately from all the pollen in the air that's being carried by the wind instead of the bees. Grasses, oaks, pines, and willows are all wind-pollinated plants that don't need insects at all. They have simplified flowers without petals that release lots of pollen for the wind to carry. What's odd is that these are the same plants that dominate the landscape. Does this mean that attractive flowers are unnecessary and could become obsolete?
Male pollen-bearing catkins on Coast Live Oak (Quercus agrifolia). The female flowers appear later and are less noticeable. This is the dominant tree in our local Central California foothills. The simplified flowers have no petals. They're attractive enough once you notice them, but their job is to shed pollen in the wind, not to attract insects (or people). Pines and other conifers, willows and cottonwoods, walnuts and box elder, all grasses, sagebrush, coyote bush, saltbush, many weeds, and many more local species are wind-pollinated plants that don't need insects for pollination. Does this mean that our familiar flowers that need insect-pollination are doing it the hard way and might disappear?
Wind-pollination is a relatively new adaptation for the oaks and grasses that dominate the valleys. It works well for plants that grow in large stands in open areas. Insects are more selective. They can fly and pollinate the uncommon plants that are scattered in more isolated habitats like rock outcrops. Flowers and insects evolved together, but this makes the plants vulnerable when their insect pollinators are threatened by pesticides and urban development. I worry that our attractive wildflowers could be replaced by this simpler community of wind-pollinated weeds and grasses.
Graybear's short reply was "I'd say the answer is similar to the toad stumper." I had to think about that. I guess the connection is that nature has many strategies, and they all work (so far), no matter how unlikely they seem to us. Good enough, but the details are still interesting and surprising.
Gymnosperm pines and other conifers have always been wind-pollinated, so it's an ancient strategy that is usually considered a "primitive" feature in textbooks. ("Conservative" might be a better term.) Angiosperm flowers co-evolved with insects and other animals into more elaborate floral structures with petals and enclosed ovaries and other features to attract pollinators and protect their pollen and seeds. Some groups like orchids and milkweeds are highly specialized for particular pollinators. But other flowering plants have simplified their flowers, becoming more like the pines.
Wind-pollination is a trait that has reappeared independently in many plant groups relatively recently in geological time. Whole plant families like the grasses (Poaceae) and oaks (Fagaceae) are wind-pollinated, as are some particular groups within families that are otherwise insect-pollinated, like sagebrush (Artemisia) and ragweed (Ambrosia) in the sunflower family (Asteraceae). Charles Darwin called it "an abominable mystery" that fossil angiosperm pollen is suddenly widespread during the Cretaceous about 130 million years ago. New research now suggests that flowering plants first appeared during the Permian Period, 250+ million years ago. Wind-pollinated grasses only became abundent about 30 million years ago in the late Oligocene, perhaps in co-evolution with large grazing mammals. Nature has many successful strategies, and sometimes simpler works as well as more complex.
There are other examples of "retro-evolution," species that seem to evolve to a simpler form. Marine mammals have gone back to the ocean and more or less lost their mobility on land. There's a continuum between sea otters and seals and whales. Primitive birds like ostriches and rheas are flightless, but so are more specialized penguins. Grouse, quail, chickens, and wild turkeys also don't fly much. There are many parasitic species that are barely recognizable because they have lost so many of the typical characteristics of their ancestors.
The orange strands on the right are the stems of the parasitic plant Dodder (Cuscuta californica) growing on Wild Cucumber (Marah fabaceus) on San Marcos Pass near my home. After it sprouts, dodder lacks leaves, roots, and chlorophyll, though it does quite well growing as a parasite on many host plants. It has tiny bell-shaped flowers in summer that show its relation to the Morning-Glorys. Dodder is now placed in its own family, the Cuscutaceae. It reminds me of the classic Invasion of the Body Snatchers movie.
Dodder (Cuscuta californica)
Wind-pollinated plants tend to have a cluster of features in common:
- Abundant pollen production and a high pollen/ovule ratio
- Usually dioecious or monoecious, with separate male and female flowers, often on different plants
- Most flowers open at the same time
- Female flowers open after the male, to avoid self-pollination
- Small pollen grains with smooth surfaces that are easily transported by wind
- Large and exposed stigmas and anthers, the males are often arranged in catkins
- Small or absent petals
- No nectar (willows are an exception)
- Flowers are held high on the plants and at the tips of branches to catch the wind
- Usually dry or temperate climates, since rain settles the pollen from the air
Coast Live Oak
Gray Pine aka Digger Pine
Wind-pollination makes sense for plants that grow in large stands in open areas where the wind can easily carry pollen between plants. I'm not surprised that these are often dominate species. Here in Central California, oaks and grasses dominate the valleys, pines dominate the high mountains, and willows and cottonwoods and walnuts dominate the river banks. All are wind-pollinated. The big exception is the coastal and mountain chaparral, though there are wind-pollinated species there as well, like Scrub Oak and Brewer's Saltbush and California Sagebrush.
I'm really worried about the habitats that are being taken over by wind-pollinated introduced grasses and weeds. I've been around long enough to remember the fields of wildflowers along Highway 154 in the Santa Ynez Valley in the spring of 1973. That started my interest in local natural history! Now it's almost all grass, and insect pollinators are scarce. I went through my slides from 30 years ago when I first noticed wild flowers, but they are mostly nice close-ups of flowers that don't show the landscape. The photo on the right shows a mass display of California Poppies in the Temblor Range on the eastern edge of the Carrizo Plain in April 1973. Now this remote place is a National Monument, and it should be. It's beautiful how the flowers favor the south-facing slopes. (Why?) It would be a valuable project anywhere to collect old photos and take new pictures of the same places to see what's changed. Memory is not reliable, but photos are hard evidence. There are many factors at work in the changing landscape, including our extended drought in the 1980s and over-grazing. But aggresive invasive species and wind-pollinated grasses and weeds seem to be taking over. It's evolution in action, but it's not the future I want.
Carrizo Plain, April 1973.
Dunn Middle School did a hike last week at the UCSB Sedgwick Reserve up the south-facing slope of Figueroa Mountain. Thanks Mike, Rick, Barbara, and everyone else! The upper slopes looked like a war zone between the California Poppies and other wildflowers and the introduced grasses. With little rain early this year, followed by a wet spring, the grasses are running ahead. It's harder to assess the pollinators. Every year is different!
Nature has many strategies that have worked up until now, but the times they are a' changing. I hope all those diverse strategies will continue to work!
On our school hike at Sedgwick, we encountered this mean fellow. This impressive rattlesnake really has nothing to do with my stumper, but it's such a cool photo I just had to include it.
I think it's a Southern Pacific Rattlesnake (Crotalus viridis helleri) Everything about this snake said to back off, and we did. He's a potent reminder that nature doesn't just belong to us. We should be stewards of the land, not just owners.
Southern Pacific Rattlesnake (Crotalus viridis helleri)
Here are some links for further research:
- I'm working to put up my own local flora with info and 1000s of photos this summer on my server at www.treebeard.org. Until then, there's good info and pictures at CalFlora.
- I couldn't find much specific info on wind-pollination on the Web. Britannica.com has useful articles on angiosperm paleobotany and evolution and many other topics. Dr. Sean Carrington of the University of the West Indies has a nice overview of The Plant Kingdom. The journal Conservation Ecology has a special issue on pollinator declines. CalEPPC, Noxious Times, and the TNC Wildland Invasive Species Program have good info and links on invasive weeds in California.
- Palynology is the study of pollen. There's a (too) cute introduction for kids at Kid's Palynology and real info from the University of Arizona. The International Organization Of Paleobotany hosts a database of fossil plants.
- I don't like calling conifers or wind-pollination more primitive that other plants and pollination schemes. Pines have been around longer than angiosperms, so if anything they're more evolved. As a long-time teacher, I know we just get better with age! There's an interesting article by Karl J. Niklas on the "Aerodynamics of Wind Pollination" in Scientific American, July 1987. The author reports on wind tunnel experiments that show how pine cones and other wind-pollinated flowers are "almost perfectly engineered to capture pollen from the wind." Interesting stuff if you can find it at a local library or used book store.
- I have many other stumpers about our local Santa Barbara natural history, including Introduced Species, Fall or Spring, Pastures of Plenty, Scarcity and Abundance, East-West Mountains, Endangered Species, and Too Many Toads.
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