Botanical Identity Crisis

or Why Do Genus Names Keep Changing?

When I posted about spring clean-up in my garden last March (Time for Spring Clean-Up), I referred to the old-fashioned bleeding hearts in my garden, the species formerly classified as Dicentra spectabilis, by their new botanical name, Lamprocapnos spectabilis. This brought cries of outrage or dismay from several readers. One commented plaintively, “Don’t tell me that they have changed the genus name of bleeding-hearts. I don’t think I can take it anymore,” and another resisted the change, noting “Afraid that Lamprocapnos spectabilis will never trip off my tongue or keyboard Jean ~ I will just stick to Bleeding Hearts from now on….”

Like others, I found myself particularly disturbed and saddened by this name change. Perhaps it’s because Dicentra spectabilis was such a pretty name for a pretty spring flower, or because this particular name was one of the first botanical Latin names that I learned. But as someone for whom scientific thinking is an important part of both my work and my identity, I also felt uncomfortable resisting new scientific knowledge. So I decided I needed to learn more about  botanical taxonomy and why it has seemed so changeable of late.

To understand this phenomenon, I talked with botanist friends and colleagues, read explanations written for a lay audience (e.g., this one put out by the Kew Royal Botanic Gardens), delved into botany textbooks, and struggled through scientific articles. Here is what I learned:

From one of my most important sources of information, the influential botany textbook, Raven’s Biology of Plants, 8th edition (published by W.H. Freeman), I learned the distinction between taxonomy and systematics. Taxonomy is the science of classifying organisms. The basic principle of taxonomy is that organisms are arranged in a hierarchical system of categories. Thus, the kingdom of plants is divided into phyla, each phylum is divided into classes, each class is divided into orders, each order is divided into families, each family is divided into genera, and each genus is made up of a number of species. The basic principle of classification is that, at any level of the classification system, plants within the same group should be more like one another than they are like plants outside that group.

But alike how? There are many different types of characteristics that can be used to classify plants. Early systems of classification were based on the appearance or habit of the plants. Linnaeus, for example, organized flowering plants into 24 classes based on the number and arrangement of stamens in each flower. Although Linnaeus’s binomial plant naming system stuck, his particular criterion for classifying plants didn’t. As botanical science developed, such arbitrary systems were replaced by “natural classifications” based on systematics – the scientific study of the diversity of plants and the relationships among them (particularly relationships based on evolution).

The dominant system being used to classify plants today is cladistics. This version of systematics is  based on the concept of a “clade” or all the evolutionary descendants of a single common ancestor. Under the principles of cladistics, “… a genus should consist of all species descended from the most recent common ancestor – and only of species descended from that ancestor. Similarly, a family should consist of all genera descended from a more distant common ancestor – and only genera descended from that ancestor.” (Raven’s Biology of Plants, 8th edition, p. 238)

In earlier taxonomies based on cladistics, the evolutionary relationships among plants were hypothesized based on observable characteristics. All this changed with the development of “molecular systematics.” Just as genetic sciences have enabled biologists to map the human genome and the genomes of many animals, so too have the genomes of plants been mapped, enabling botanists to see which plants are most closely related to one another. This can sometimes lead to big surprises. For example, without the evidence of plant DNA, no one would have guessed that the water lotus (Nelumbo) is more closely related to sycamore and plane trees (Platanus) than to water lilies! (Raven’s Biology of Plants, 8th edition, pp. 242-3)

In 1997, a group of botanists (Magnus Liden, Tatsundo Fukuhara, Johan Rylander, and Bengt Oxelman) published an article in the scientific journal Plant Systematics and Evolution entitled “Phylogeny and classification of Fumariaceae, with emphasis on Dicentra s. l, based on the plastid gene rps 16 intron.”  This formidably named article was an application of the new molecular systematics to the Fumitory plant family (Fumariaceae), which includes the genera  Dicentra and Corydalis (among others), and used a particularly important gene to examine the evolutionary relationships among these plants. What the authors found was that Dicentra spectabilis did not share a common immediate ancestor with the other Dicentra species and therefore, under the principles of cladistics, did not belong in the same genus.

There have been some reports in the garden blogosphere that the entire Dicentra genus was disbanded. That doesn’t seem to be the case. The very similar looking North American native plants Dicentra eximia and Dicentra formosa still seem to be classified as Dicentra; it’s just that the plant formerly classified as Dicentra spectabilis turned out not to be as closely related to these as had been assumed from their appearance. As Liden et al. explain, “A splitting of Dicentra, with the consequence that the name of the commonly grown D. spectabilis will have to change, is unavoidable if we aim at a reflection of evolutionary relationships in our formal classification.” (p. 414)

But granted that taxonomic integrity required renaming this favorite plant, why did they have to give it such an ugly name? Why replace the soft sibilant sound of Dicentra with the hard, explosive p sounds of Lamprocapnos. It turns out that scientists who propose taxonomic changes cannot just use any names that they want; plants names are governed by a set of rules set out in the International Code of Botanical Nomenclature. And one of those rules is that pre-existing names get precedence. It seems that the family connections of Dicentra spectabilis had long been suspect and that as early as 1850 a published article had given it a different genus name. That name? Lamprocapnos.

While we may grouse about the genus name of this plant, everyone is agreed that the species name, spectabilis, which means spectacular or showy, is apt! Whatever we call it, this wonderful spring bloomer is likely to remain a garden favorite.