Nomenclatural Frustration

Agropyron molle, Agropyron smithii, Agropyron smithii var. molle, Agropyron smithii var. palmeri, Elymus smithii, Elytrigia smithii, Elytrigia smithii var. mollis and Pascopyrum smithii are all names for western wheatgrass. Is this a mess, or what? We’ve all heard the argument that scientific names are preferable to common names because they are unambiguous and understood all around the world, but clearly this is not always true.

Of course, I’ve deliberately chosen an exceptionally messy example, but gardeners and botanists have all experience an inconvenient name change in a favorite plant. (Should pasque flower be Anemone or Pulsatilla? Is pincushion cactus Coryphantha or Escobaria?) Why can’t scientists make up their minds and settle on a single name? The answer: that is not the nature of science.

Carl Linnaeus, the father of
scientific nomenclature

Taxonomists, like all good scientists, adjust their hypotheses and conclusions when new evidence becomes available, and in the last decades a wealth of new evidence has become available. Since the time of Linnaeus (1707-1778), characteristics of the sex organs of flowers have been the most important features used in taxonomy, so that plants with similar flowers were placed into the same group. Linnaeus’s goal of organization, however, is not the goal of contemporary taxonomists. Now, we strive to organize plants into “natural groups,” groups that reflect common ancestry, not morphological similarity (though that can be a valuable clue).

In the last 30 years, many mysteries of molecular evolution have been at least partially resolved. Complex algorithms and DNA sequencing have made it possible to propose new taxonomic categories that more closely reflect our understanding of evolutionary patterns of both genotypes and phenotypes, and this has led to the rearrangement of groups and consequent necessary name changes. These changes have occurred at all taxonomic levels, from phylum down to subspecies, but are most noticeable when genus or species names are changed. Don’t be annoyed—think of it as progress and be glad that some botanist likes your favorite plants enough to work on them. Besides, since taxonomists don’t all agree on which algorithm is best, or on which DNA sequence most reliably represents evolution of the group, and new algorithms and genes are proposed, we can expect the changes to keep on happening.

Western wheatgrass

So, which name for western wheat grass is best? That depends on just which characteristic you think is most important in discriminating among species in the complex group that includes western wheat grass. In this case, the best name might just be the common one—we all agree on that one.

Written by Dorothy Tuthill—who used to be known by a different name