Botany Rules: Why Change Scientific Names?! Part 2

stiff sunflower Helianthus rigidus
when the photo
was taken, now Helianthus
pauciflorus

     Plant names of American plants are changing more right now than they have for centuries because of the joint impact of the Flora of North America Project and DNA sequencing. I talked about the Flora of North America project last post.  LINK   

  There would certainly have been changes in American plant names as a result of the writing of the Flora of North America, but the concurrent emergence of DNA sequencing has produced surprising new data to integrate. 

      Compared to animals, plants have a simple structure. Botanists recognize only three tissues: root, stem and leaf. Flowers and fruit are specialized leaves. From descriptions of the arrangement and details of these three tissues botanists created plant classification. They used all the tools they had: complex measurements, chemical analysis, geographic patterns, and ability to hybridize, for example. 

  

     After 400 years of applying these techniques, plant biologists thought they were pretty close to having found the true relationships among plants. They were wrong. DNA data has revealed many surprises. In particular, it has shown convergence, where two plants look very similar but turn out not to be closely related at all. For example, flowering plants living in ponds or streams have similar characters for living in or under water, but their ancestors are found all over the plant kingdom. 

milkweed, genus Asclepias

    The reverse happens too: very distinctive subgroups of plants are turning out to be members of other plant groups, as revealed by their DNA similarities. One such change was at the family level. The milkweeds, a very distinct group with milky sap, unusual flower structure, pollen in clumps, and pods with winged seeds, turn out to be a subset within the plant family Apocynaceae. DNA evidence caused the milkweed family Asclepiadaceae to be discontinued, and now the milkweeds are classified within the Apocynaceae (the dogbane family. I could call the Apocynaceae the milkweed family if I wanted too (see post on families).) 

    The net result of the DNA evidence is that plant names are the most unstable right now that they have been in centuries. New information is causing botanists to combine and separate plants in unexpected ways. The nonspecialist just has to adjust as the changes appear. 

 Are We There Yet?   I don't think so. There will be more changes. Only half of the Flora of North America has been published and probably only a small percent of the genera in North America have been subjected to DNA study, so changes can be expected to continue. Beyond that, excluding Mexico was necessary to make the Flora of North America feasible but plant ranges and relationships extend across the border and when they are added to the picture, the relationships may need further revision. And South American or Eurasian species will have to be included before some groups make sense. 

 How Does Anyone Keep Up?  My method has been to use the scientific names in a reliable reference. I used the Flora of the Great Plains  for years. I didn’t decide for myself whether chamomile was Chamomila or Matricaria, I simply used the name the Flora of the Great Plains used. Today that method is easiest based on a website. I’d go with the Flora of North America (link) but it is only half available. The USDA Plants list (link) and the USDA's GRIN taxonomy page( link) are good sources for North American plants. The latter is more technical. Rely on a well-known reference and you don't need to make decisions about  plant names.

    Looking beyond North America, there is no quick answer. We're a long way from a world flora website with all the world's plants in one place and carefully evaluated--tho that is certainly coming. In the meanwhile, many regions have good floras in print and online, for example the Flora of Europe was published in five volumes in 2010, New Zealand has its flora online. Each year the web-based resources get better.  

 Isn't It Annoying? Perhaps. When explaining this to people who just want to know that the name is, unstable names are irritating. 

    On the other hand, when I explained that names are in a state of flux to undergraduate students, it was a plus. What, botany isn't a dead science?!   Oh no, it is dynamic. Things are changing and there are still surprises around the corner. 

    Try seeing the name changes as the indicator of vitality that they are.

rubber rabbitbrush, formerly Chrysothamnus nauseosus
now Ericameria nauseosum, flowers fading

Comments and corrections and questions welcome.

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 Kathy Keeler, A Wandering Botanist

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