Plant names keep changing. Some changes are based on studies that show previously unknown relationships. Plants are moved to reflect that and sometimes the names change. Other times plants are found to be the same or different and the process of merging or splitting a species creates a name change. More puzzling to non-botanists are mergers and splits based on phylogeny. Let me try to explain.
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| Pasque flower, Anemone pulsatilla |
Plants are frequently renamed these days to make the names reflect relationships.
Botanical classification is intended to indicate relationships. Plants that intercross are put in the same species. Very similar plants that cross poorly with each other become different species within the same genus. A group of genera that are similar are combined into a plant family and plant families are grouped by similarity within Orders, up to Classes, Divisions, and the Plant Kingdom. This is the description of a phylogenetic classification. To the best of our ability, the plants are grouped in relation to their evolutionary history.
A principle that underlies this classification is that groups should be monophyletic. In monophyly, the ancestor and all the descendants, as determined by shared characters, usually DNA, are all classified within the same group.
No group should be paraphyletic. A paraphyletic group is one containing the common ancestor and some but not all its descendants. When DNA or other methods detect paraphyly, the group should be reorganized to make it monophlytic.
Here is a very simple example:
This arrangement is polyphyletic. The ancestor and all its descendants are NOT in the same group (genus). It can be corrected either by 1) combining all three species into a single genus or 2) creating a third genus so each genus is monophyletic. (Or by putting species 2 into genus 2, but imagine dozens or hundreds of species affected, not just 3; usually a one-species switch won't solve the problem.)
This is a big category of plant name changes in the last decade and one that often puzzles people.
Here are some examples
Rosemary. Rosemary, known as Rosmarinus officinalis, is a mint from southern Europe. It has two close relatives, and for a long time the three of them made up the genus Rosmarinus. Genetically, however, these were shown to be a subset of the big genus Salvia, which contains about 1,000 species. Since it is so genetically close to the salvias, having rosemary in the genus Rosmarinus makes Salvia polyphyletic. To make Salvia monophyletic, either Rosmarinus and a couple other small genera needed to be merged with Salvia, changing about 15 names, or Salvia had to be broken into some l00 or so genera. Merging the little genera into Salvia required about 15 plants to change their names; breaking up Salvia would have renamed over 700 species. You can see why Rosmarinus was merged with Salvia. There was already a Salvia officinalis, so Rosmarinus officinalis was changed to Salvia rosmarinus.(My blog: What happened to Rosemary link)
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| rosemary, Salvia rosmarinus |
One of the other 1,000 Salvia species, azure blue sage, Salvia azurea.
Mahonia. Mahonia, hollygrape, Oregon grape, was a genus of about 70 species found in the Americas and Asia. Berberis, barberries, are about 500 species found all over the world except Australia. Genetically, Mahonia is a subset of Berberis. Thus, the genus Mahonia makes Berberis polyphyletic. So Mahonia was merged into Berberis. Mahonia aquifolium became Berberis aquifolium and Mahonia repens became Berberis repens, etc.
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| Berberis repens, creeping hollygrape |
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| Japanese barberry, Berberis japonica in winter |
Pulsatilla. Pulsatilla was a genus of spring wildflowers, often called pasqueflowers, growing across the Northern Hemisphere. With distinctive flowers and seed heads, they formed a genus of about 40 species. However, DNA studies show Pulsatilla is a subgroup within Anemone and, therefore, Anemone was polyphyletic. There are 120-150 species of Anemone, called anemones or windflowers, native all over the world. So Pulsatilla species became Anemone species, for example Pulsatilla patens to Anemone patens. The widely-planted European Pulsatilla vulgaris had to become Anemone pulsatilla because there was already an Anemone vulgaris. See first photo of this post.
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| the distinctive seed heads of a pasque flower, in this case Anemone pulsatilla |
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| windflower, Anemone |
Buffalograss, Buchloë dactyloides - Buffalograss was the only species in the genus Buchloë. It is a highly successful plains grass, with a range from Mexico to Canada. Its closest relatives are little-known grasses confined to small areas in Mexico. All of them are very closely related to the grama grasses, Bouteloua gracilis, B. hirsuta and relatives. Nobody minds if one-species genera of small obscure grasses are merged with Bouteloua, but if you do that, then buffalograss should become a Bouteloua too, or Bouteloua is polyphyletic. So it is now Bouteloua dactyloides. I liked the sound of Buchloë, but Bouteloua is fun to say too. I won't miss having to remember to put the dots over the e in Buchloë.
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| buffalograss, Bouteloua dactyloides |
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| blue grama, Bouteloua gracilis |
There are other name changes that are the result of making plant classification monophyletic. One of them is red valerian (Centranthus, now Valeriana) link
In a way, scientific names are democratic, because although there are rules for naming, people have to accept the changes. So pointing out polyphyly and proposing a solution does not mean botanists are necessarily going to use the new names. Or, not right away. Mostly, I have observed that, over time, the changes gradually take hold. They are, of course, more coherent than having most genera monophyletic and one or two polyphyletic.
There is an "out clause" for accepting a polyphyletic group. One group that is polyphyletic and will stay that way are the classes of vertebrates: birds and mammal are, evolutionarily, types of reptiles and if not classified as reptiles, make reptiles polyphyletic. But zoologists argue that there are dramatic evolutionary innovations in both groups (warm-bloodedness, flight and more) that justify giving them a rank equivalent to reptiles. Botanists allow the possibility that a major evolutionary innovation can permit breaking the monophyly rule, but they reserve that for extreme situations and try not to invoke it.
You can expect more of this kind of name changes. Each year DNA testing is done on more families and genera. The technology has been available for decades, but there are thousands of genera to test (13,000 Angiosperm genera, according to Google.)
Also causing reclassification is that botanists are increasingly working outside of traditional borders. The Flora of North America, which has been really important for organizing plants from scattered states, is actually The Flora of North America North of Mexico. It is 30 volumes long, so stopping at the southern US border made sense. But plants and their relatives don't stop there; many species and genera and most families, are found in Mexico and farther south as well. Other genera, like columbines (Aquilegia) have species in North America, Europe, and Asia. We have a long way to go to look at the DNA in all the species in plants with multinational ranges and no doubt more polyphyly will be detected and more familiar names will proposed for change.
Comments and corrections welcome.
References
Drew, B.T., J. Gonzalez-Gallegos, C.-L. Xiang, R. Kriebel, C. P.. Drummond, J. B. Walker and K. J. Sytsma. 2017. Salvia united: the greatest good for the greatest number. Taxon 66 (1): 133-145.
Judd, W.S., C. S. Campbell, E. A. Kellogg, P. F. Stevens, M. J. Donaghue. 2008. Plant Systematics. 3rd ed. Sinauer Associates, Inc. Sunderland, MA.
Whittemore, A. T. no date given. 3. Berberis Linnaeus, Flora of North America. link
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