Tuesday, August 12, 2014

Coleus - I am calling your name! (But what is it?)

Many gardeners and naturalists are frustrated when we botanists change the scientific names of species. I feel frustrated too, when the crown vetch changes its gorgeous, easy-to-remember (for me) name Coronilla varia, to Securigera varia. Now the genus name sounds like a financial security company, not like a gorgeous crown of pink flowers.

But change happen, and it happens for a good reason. We are sorting out old problems and making things better and more logical in the long run. Keep on reading and you will find out what
Coleus hybrids.
(cc) photo by Pharaoh Hound on Wikimedia.
Wild species change genus for mainly one reason. We try to classify all species with their closest relatives, so that everything in a genus comes from one common ancestor species. That means, all species has one origin back in time and share a common history. To figure out this history and these relationships we use DNA and morphology, and build up evolutionary trees that shows the story of species evolution over time.

Of course, when most plants were first described, they weren't part of evolutionary studies. We first started to construct evolutionary trees using DNA and computers in the late 1980s. In the beginning of botanical taxonomy at Linnaeus' time we didn't even know about evolutionary theory, since that came about in the 1860s with Darwin. The start date for botanical nomenclature is Linnaeus book Species Plantarum from 1753. Before recent times, scientists gave species their scientific placement and names based on overall similarity or dissimilarity, not evolutionary relationships.

In the blogpost about "Magilla Perilla" we listed the scientific name for coleus as Solenostemon scutellarioides. We also listed two older synonyms as Plectranthus scutellarioides and Coleus blumei. A few weeks ago we e-mailed botanist Alan Paton, who works on the evolution of this plant group at Royal Botanic Gardens, Kew in London, and asked him, "What is the correct species name for coleus, for real, and where does it belong?" 

His answer was maybe not what you expect. He said:
"I'm writing up the research at the moment. [...] Plectranthus including some other genera on one hand and Coleus and some other relations including Solenostemon form sister clades. The actual picture with denser sampling shows a slightly more complex picture than these earlier papers; but they give an outline which suggests Coleus should be recognized and Solenostemon would be embedded within it."

What does this mean?  Be prepared to see the scientific name your garden coleus change back to original genus Coleus in the near future, and Solenostemon will be no more (it will be merged into Coleus). Plectranthus will still be around but with fewer species and not include your garden coleus. So, coleus will be a Coleus again, which is very nice, and certainly easy to remember. It has been a mess with these names, but Alan is sorting it all out, once and for all. Check back here on the Botanical Accuracy blog when his paper comes out for an update.

It is really all about getting the right species in the right place in the giant evolutionary family tree, which includes over 300 000 plant species in the world. No wonder it is a little chaotic at times. But we have to do it, and we have to use the most updated scientific names possible to talk to each other about plants and understand our plants, across over the world. It is all part of the progress of knowledge.  And sometimes increased knowledge isn't that convenient to begin with.


Paton, A. J., et al. Phylogeny and evolution of basils and allies (Ocimeae, Labiatae) based on three plastid DNA regions. 2004. Molecular Phylogenetics and Evolution 31: 277-299.

Lukhoba, C. W., M. SJ Simmonds, & A.J. Paton. 2006. Plectranthus: A review of ethnobotanical uses. Journal of Ethnopharmacology 103: 1-24.

'What is in a (PLANT) name?' on the FLORIDATA website