By David Spector Gazette Contributing Writer
In the fall, yellow goldenrods and pink to violet asters provide a colorful foreground to the changing leaves of trees. Such flowers are examples of fall composites, members of the aster or composite family. (The name “composite” refers to the flower head consisting of numerous small flowers. The scientific name for this family, Asteraceae, indicates their shared similarity to asters.) For a naturalist who wants to put a name on each species, the fall composites also provide a challenge—and sometimes frustration—as the many similar species can be quite difficult to identify.
Among these fall composites is an example of spectacular invisibility. I am not referring to the kind of invisibility that requires a microscope or other specialized instrument to reveal, but to the kind of invisibility that too often attaches to aspects of nature that are easily observed but pass unnoticed because we’re accustomed to look for certain kinds of plants and not others. When I drive New England roads in the fall I am often struck by a roadside spectacle that is invisible to many: the giant spires of wild lettuce.
Wild lettuces can be recognized by their growth into tall narrow plants with spiky, dandelion-like leaves and inconspicuous flowers that quickly give rise to little tufts of wind-dispersed seeds. These plants, starting from ground level, grow to great heights in a single growing season. I estimate some of the lettuces I see in late summer and early fall to be around 10 to 12 feet high, about twice as tall as a human.
Although many plants and animals are larger than lettuces, few grow in height as rapidly. A rough comparison of growth rates shows that wild lettuce compares well to some more famous organisms (approximate numbers chosen for convenience of calculation): lettuce, two feet per month (based on growing about 12 feet in about six months); redwood, one inch per month (based on a generous 300 feet in 300 years); humans, 0.33 inches per month (based on six feet in 18 years). Of course, a comparison based on girth or weight would not give as much favor to the lettuce; plants, like athletes, need to be careful about picking the events in which to compete.
From the perspective of lettuce, the rapid growth and great height is not a matter of competition with redwoods or humans, but probably of competition with other lettuces of the same species. Taller individuals may be more likely than their shorter neighbors to be pollinated and better able to distribute their seeds widely. Thus, taller individuals would be more likely to leave offspring in the next generation.
One of the many things that amaze me about lettuce is that some humans a few thousand years ago recognized that the young leaves of an “Old World” plant very similar to the ones towering over New England roads could be eaten—the mature leaves of many species are bitter and some are poisonous— and then domesticated it and bred remarkably different varieties. (Some 300 species and subspecies of wild and domesticated lettuce all belong to a single genus, Lactuca. The name derives from the Latin word for milk, lac, referring to the milky sap of mature lettuce plants.)
The contrast in form between the balled-up convolutions of iceberg lettuce and the graceful towers of wild lettuce is as great as that between a lap dog and a wild timber wolf, both examples of the power of artificial selection that was part of the inspiration for Charles Darwin’s formulation of natural selection as an explanation of evolution.
David Spector is a former board president of the Hitchcock Center for the Environment and teaches biology at Central Connecticut State University.
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