Ragweed

What’s blooming in the area: Tea roses, Apache plume, butterfly bush, trumpet creeper, Japanese honeysuckle, silver lace vine, leather leaved globemallow, sweet pea, alfalfa, white sweet clover, Russian sage, velvetweed, scarlet beeblossom, white and yellow evening primroses, datura, Heavenly Blue and ivy-leaf morning glory, scarlet creeper, bindweed, goats’ head, purple phlox, bouncing Bess, pale trumpet, stickleaf, clammy weed, spurge, purslane, pigweed, Russian thistle, winterfat, ragweed, snakeweed, native and farmer’s sunflowers, Hopi tea, gumweed, horseweed, wild lettuce, strap-leaf and hairy golden aster, woolly paper flower, goldenrod, tahokia daisy, black grama grass; buds of heath and purple asters; new áñil del muerto plants.

What’s blooming in my yard, looking north: Zucchini, nasturtium, Mexican hat, chocolate flower, blanket flower, black-eyed Susan, chrysanthemum.

Looking east: Floribunda rose, California poppy, hollyhock, winecup, sidalcea, snapdragons, Maltese Cross, Jupiter’s beard, coral beardtongue, large-leaved soapwort, scarlet flax, sedum, garlic chive, Maximilian sunflower.

Looking south: Blaze roses, rose of Sharon, Crimson Rambler and reseeded morning glories, zinnia, cosmos.

Looking west: Caryopteris, flax, catmint, calamintha, lady bells, sea lavender, David phlox, leadplant, perennial four o’clock, purple ice plant, Silver King artemisia, purple coneflower, Mönch aster; some peaches survived the spring frosts.

Bedding plants: Moss rose, sweet alyssum, tomato.

Inside: African aptenia and asparagus fern.

Animal sightings: Rabbit, geckos, hummingbird, bees, large black harvester and small dark ants, grasshoppers.

Weather: Continued hot afternoon winds and late clouds rather than usual monsoons; last rain 8/24/2009; 13:41 hours of daylight today.

Weekly update: Somehow, from bits of urban legends, facts half remembered from grade school, and trivia passed on at summer camp or, later, by friends at work, we cobble together a collection of facts about the natural world we absolutely believe to be true.

Everyone knows cockroaches are older than dinosaurs and ginko trees are the oldest living fossils. I had my own idea that plants like ragweed with male and female green flowers so inconspicuous they could only be pollinated by the wind were nearly as old as the ginko.

We cede these survivors of the cataclysm that destroyed the dinosaurs great powers of adaptation.

And sometimes we’re at least partly right. Cary Easterday found a nearly complete fossil of a giant cockroach from the 300 million-year-old Carboniferous layers of an eastern Ohio coal mine in 1999 that predates the dinosaurs. However, it’s closer to the insects found today in the tropics than to our domestic insect which comes from the Cretaceous that followed the extinction of the giant reptiles. It’s the genus that’s ancient, not the species.

Ragweed, like cockroaches inhabiting city apartments, will not be killed. Increase the carbon dioxide in the air and it still germinates. Throw salt on the road in winter and ecotypes germinate before the salt’s disappeared from the soil. Mow it down and it comes back in two weeks with flowering stalks below the level of a blade.

Spray it with herbicides, it develops strains resistant to Round-up and ALS inhibitors. Give it a hard spring that won’t encourage growth, the seeds resume dormancy and can wait 20 years to germinate. Let the surrounding vegetation get too luxurious, it produces short, female-only plants that go to seed.

Well, plasticity’s the only part about ragweed that fits the naturalist’s equivalent of an old wive’s tale. Ambrosia artemisiifolia, in fact, is a member of the composites, one of the more recent plant families, dating to sometime in the Cretaceous, the era before our modern continents formed when bees were just emerging Ginko fossils go back to the Permian, that geologic time between the Carboniferous of the giant cockroach and the Triassic of the dinosaurs.

Ragweed was one of the first plants I could distinguish as a child by its determined geometricalness. The divided, grey-green leaves spread parallel to the ground and at ninety degrees to each other. Later in the season the leaves changed shape and location, but by then I recognized the tapering flower spikes that looked like the square weave on a lanyard with openings between each layer where green caps repeated the pattern of the lower leaves.

Because I could identify the plant from a distance, I never bothered to look at it closely. This year’s unusual mix of rain, heat, and cold may have encouraged the flowers to expand more than usual to interrupt the expected color pattern. Last Sunday was the first time I ever saw a reason to pick a spike.

Under the green heads of five sepals, that cover the flower clusters before they’re ready to bloom and give the upper spikes their green appearance, is a round yellow bud, surrounded by a single ring of similar buds. There looked to be six or seven outer buds near the base of the spike, but maybe four toward the top. Along the spike, only a few of the male flowers had three anthers pointing down to release the hay fever causing pollen.

I was somewhat gratified to discover scientists can be as fooled by their early assumptions as lay people like me. Although they know the pollen can blow for miles, botanists have always assumed the grains dropped directly down to the female flowers placed where the leaves join the stem. Then, Jannice Friedman and Spencer Barrett watched some ragweed flowers and found most of the female flowers aborted if they detected pollen from their own plant and plants grown in isolation produced far fewer hard seeds than those au naturel.

But even then they realized the common ragweed would adapt. Deprive them of the pollen they need, and they’ll overcome their self-incompatibility to make do with what appears. No one yet has proven the green weed won’t survive Armageddon.

Notes:
360-286m - Carboniferous - hot - oldest cockroach - evergreens
286-248m - Permian - glaciers in southern hemisphere - more insects - deciduous trees - ginko
248-213m - Triassic - hot and dry - Gondwana breaks away - dinosaurs - ferns
213-144m - Jurassic - seas advance - dinosaurs - earliest birds and flowers
144-65m - Cretaceous - swamps - dinosaurs extinct - bees - modern cockroach - composites
65m-2m - Tertiary - drier - modern continents form - sea animals - grasses
2m- - Quarternary - glaciers come and go - modern animals and plants

Bazzaz, Fakhri A. "Ecophysiology of Ambrosia artemisiifolia: A Successional Dominant," Ecology 55:112-119:1974.

_____. Plants in Changing Environments, 1996.

Friedman, Jannice and Spencer C. H. Barrett. "High Outcrossing in the Annual Colonizing Species Ambrosia artemisiifolia (Asteraceae)," Annals of Botany 101:1303-1309:2008.

Lee, Chad, Karen Renner and Jim Kells. "ALS- Resistant Common Ragweed in Michigan," Michigan State University Field Crop Advisory Team Alert for 23 March 2000.

Lundholm, J. T. and L. W. Aarssen. "Neighbour Effects on Gender Variation in Ambrosia artemisiifolia," Canadian Journal of Botany 72:794–800:1994.

Ohio State University. "Largest Fossil Cockroach Found; Site Preserves Incredible Detail," news release, 7 November 2001.

Pollard, Justin Michael. "Identification and Characterization of Gylphosate-Resistant Common Ragweed (Ambrosia artemisiifolia L.), University of Missouri-Columbia, 2007.

Antonio DiTommaso. "Germination Behavior of Common Ragweed (Ambrosia artemisiifolia) Populations across a Range of Salinities," Weed Science 52:1002-1009:2004

Photograph: Ragweed growing along the road by my house, 23 August 2009; most are buds, but it looks like the anthers are extended on one flower to the left of the stem above the long leaf.