“In introgression, what often seems at first sight to be the appearance of something totally new usually proves to be a recombination that one had not had the wit to anticipate. Hybridization ordinarily results not in the new, but in the unexpected.” — Edgar Anderson 1949, Introgressive Hybridization
When I left for California on October 20, the leaves had just started turning in our area. When I returned five days later, it was the peak of fall color. Everyone the past few days has been raving about yellow. I ran into a friend at the Field Museum today who confessed that before this past weekend she’d never been to the Arboretum. She spoke in a reverie of the leaves falling like snow. What are they, she asked. She is a tropical botanist and knows, I suspect, more plants than I ever will; tropical botanists always seem to. They are sugar maple leaves, I told her. She had spent two and a half hours in the East Woods, just walking around. Friday, my wife sent photos of trees and puffballs, also from the East Woods. I have run into colleagues on the path outside our building smiling at nothing this past week, looking up into the air. We seem to have been caught off guard by beauty.
The streets are slick with foliage. Leaves are piling up in Maple Grove Forest Preserve. The paths and forest floor and riverbank are mottled in shades of yellow, brown and white, irrespective of what lies beneath. On my Sunday morning walk, I missed the turn onto my typical path and had to retrace my steps to find the entrance. The wood nettles and touch-me-nots that hemmed the trail edges here a few weeks ago are shrouded in frost-withered foliage. Poison ivy and carrion flower leaves are cracking from the stems. Zigzag and elmleaf goldenrods have gone to seed, carrion flower berries are still hanging onto a few plants. Burning bush fruit valves are clinging to the branches. The margins of wild ginger leaves are glowing yellow, and the darkest greens on the forest floor are the evergreen leaves of Carex albursina and C. jamesii. Soon they’ll be lying under the snow, waiting patiently for spring, while the less hardy forest herbs are hiding under ground.
Last week’s trip to UC Davis for the International Oak Society conference was filled with friends and walks along the river edge from the hotel to the conference, further on to the magnificent oak collection. I’ve never been fond of cultivars, but the hybrids there are arresting: crosses between bur oak of eastern North America and valley oak of California; Quercus turbinella of the southwest and Q. virginiana of the southeast or Quercus robur of Eurasia and northern Africa. That making such a thing should result in beauty is remarkable to me. There is something stark about these hybrids, something moving about the way the characters of one species stand out in relief against the genetic background of another. The enormous acorn caps of bur oak seem somehow larger when they are darkened, bell-shaped, with the marginal scales inrolled instead of forming a fringe around the edge; and yet the apices of the scales shingling the back of the cap are slender and elongate. That, evidently, is the effect of putting Quercus macrocarpa into a Q. lobata background. A hybrid is like the final cut of “Pharaoh’s Dance,” so heavily edited that at first you don’t notice as you glide over a splice from one take to the next. Which species contributed this acorn stalk, this leaf apex? I can look a dozen times before I even start to think of asking this.
The beauty of maple leaves notwithstanding, my head is packed full of oaks and phylogenies and hybrids these days. I have just finished Edgar Anderson’s Introgressive Hybridization, and I don’t know if I’ve ever met a more clear-headed person. Pick it up if you haven’t read it, if only for sentences like, “This is one of those simple techniques that are more important than they seem. Everyone who has tried it has learned unexpected things about the material he was studying.” Does the subject matter even concern you if you get sentences that universal out of the deal? So much the better for you if you are interested in hybridization. You’ll glide through the day on wet maple leaves.