Field of Science

A rose, is a rose, so how does I knows?

Our woody plant horticulturalist stopped by yesterday with a piece of leafy twig. "What do you think this is?" he asked. Hmm, after assessing the specimen, I said, "Well, it's in the rose family." He already had guessed that, but beyond that it wasn't obvious. Now this particular specimen turned out to be a bit unusual, a species I had never seen before, and if that were not the case, he wouldn't have needed my input at all. This particular specimen proved to be a tree quite uncommon in this area (Sorbus aria, whitebeam). After visiting several references, several possibilities were eliminated, and it wasn't until I tried an old woody plant identification key, one that includes ornamental species, that things began to make sense. This species has a simple leaf and most species of Sorbus have pinnately compound leaves, a single axis with two rows of leaflets. Well and good, between the two of us, we nailed the ID and felt pretty good about ourselves.

But here's the thing. Neither one of us ever considered any other possibility after initially deciding this plant was a member of the rose family, instead of one of the other 700 or so families. Now the rose family is a pretty big group of plants, 100-120 genera and 3000 to 3500 species. What made us decide rose family?

It's strange but I don't actually know. Of course I can recite a list of characters, but most of them were not present because there were no flowers or fruit. Yet this twig, with its dozen and a half leaves and buds somehow just looked "rosy". My first thought was a pear, but this specimen's leaves had a double saw toothed margin (pear's are mostly smooth edged), wooly white hairs on the back side of the leaves (never seen a pear like that), and rounded buds (pears are usually more pointy). OK so not pear, more cherry like, but the bark was very un-Prunus, no horizontal lenticels and shiny buds. And finally by a process of elimination I ended up at Sorbus, even though the leaf seemed all wrong (simple leaf rather than pinnately compound). Once this hurdle was cleared, the details fell into place. Score one for the botanist.

This is the hard thing about plant identification. At a certain point, you have enough experience, that you can simply use a gestalt. Some sort of search image is triggered that shoves you in the right direction. And even though I have been teaching such courses for years, I just don't know how to teach this. You simply must work at identifying plants long enough and if you are good, this sense comes to you.

I play a dirty trick on students learning plant ID by giving them two very closely related plants sequentially, sometimes the same species, but just with different colored flowers or leaves. Some few look upon the 2nd specimen with a puzzled look, and then ask, didn't we just do this? Some are even more certain, and toss it aside as knowing I tried a lame trick. Others without an iota of recognition labor through another step by step slog through an identification key, and act surprised when the same species comes up again. Interestingly this exercise has proven to be a great predictor of their over all performance in the course. And I wonder if this skill, this perception, is tied to the ability to conceptualize, to go past the details and grasp the essential underlying idea. Because that's how this works with plant ID. The species ID is in the details, but the broader classification, in particular the family level taxonomic grouping is in the conceptualizing of the commonalities.

That's one good thing about experience. You do get better in doing some things with age. And you can't hold a specimen up to your computer monitor and get any closer to an ID. Technology isn't making any serious inroads into such skills at all. You can scan it, or digitally photograph it, and put it on the internet, but sooner or later, it's someone like me who tells you what it is.

A long time colleague of mine once expressed his concern and apparent inability to teach such skill. "Maybe we can just rip their heads off and pour it in," he said. Sounds like fun.

1 comment:

Mary said...

Hello Dr. A.,

I just came across your blog thanks to a link from Seeds Aside. Your post addresses just the sort of thinking I'm interested in - the gestalt of an organism, be it plant or planktonic larvae.

Some time ago I learned a bird-watching term called "jizz." It means, essentially, the gestalt of a bird's flight and appearance, and it accounts for instant recognition of a bird long before you can see the details.

My background is in oceanography and I learned the jizz of plankton through the microscope. I had your feeling then about wanting to pour gestalt awareness of plankton into the students' heads.

Now that I'm retired and studying plants in Panama for the fun of it, I'm finding how painfully slow it is to get to that point!