Have you heard the news? Good old Rosemary has had a makeover. Previously known as Rosmarinus officinalis, the RHS announced (last year) that the correct name for the species is Salvia rosmarinus, which places it in the same genus as well loved garden plants like velvety Salvia ‘Amistad’ and flamboyant Salvia ‘Hot Lips’. To complicate things further, Russian Sage, a personal favourite of ours (and the bees) has been re-classified from Perovskia atriplicifolia to Salvia yungii. On the face of it, this beautiful bunch don’t seem to have a lot in common, with flowers in a kaleidoscopic variety of sizes and colours, and habits ranging from tender tuberous Salvia patens to hard(y)-as-nails Salvia nemerosa.
Elsewhere in the garden, stalwart Sedum has been remodelled as the cumbersome Hylotelephium and the unholy evil that is Japanese Knotweed has been rechristened from Fallopia to Reynoutria. As if tackling the impenetrable tangle of botanical Latin wasn’t difficult enough, gardeners now find themselves on shifting sands. Blink and you will miss the name change.
But don’t despair, this moniker mixing is all for a good reason so let’s pin down some elusive epithets and discuss how and why the names of our well-loved garden plants are suddenly up for grabs.
Since Carl Linnaeus popularised the binomial naming system in the 18th Century, plants have been grouped into families, genera and species based on their physical (sexual) characteristics. These might include the shape of a flower, the number of stamen, petals and sepals and the ability to produce fertile seed when crossed. In general, this has been extremely successful but problems arise when relationships aren’t clear cut.
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Charging in to help is modern DNA sequencing. Scientists around the world are identifying which species genetic history points to closer connection than expected, and which species are imposters in unrelated genera. Individual botanists and large international research collaborations like the Angiosperm Phylogeny Group (involving Kew Botanic Garden) are sketching new family trees based on this research. But every now and again this new understanding will cause a headache.
This brings us to Rosemary. It turns out that the three species of Rosemary share enough DNA and characteristics with other Salvias to be considered part of that group (genus) but are also sufficiently distinct to be understood as a sub-genus. In fact, research shows the Salvia genus could dissolve into 11 separate groups, each with their own special characteristics. Scientists like to be consistent; if Rosmarinus is distinct enough to be considered a full-bodied genus in its own right, why shouldn’t the other 10 possible genera? Things needed to go one way or the other, but if all the plants now named Salvia were broken down into 11 groups, all the plants in those groups would need to be re-named; that’s a total of over 700 plants!
Here, botanists have been quite considerate to us gardeners. Rather than splitting the group into 11 and changing 700 names, it was easier to include Rosemary and Russian Sage into a broad-church Salvia. I say easier…you may well be asking why we should bother re-naming plants at all! What difference does it make to roast potatoes with garlic and rosemary if it’s called one thing or another?
There are advantages to gardeners to know which plants are related. It helps us to understand which pests and diseases might jump from one plant to another, hints at the best conditions for growing and can give vital clues to possible medicinal benefits. But most of all, from Hylotelephium to Reynoutria, botanist’s continued research using DNA sequencing shows how amazing the tangled web of life really is. We will never cease to be surprised that plants separated by oceans can be so closely related!
The old system of classification was highly accurate but very occasionally DNA research will throw up an odd-ball. This means the vast majority of names will stay the same but we shouldn’t be surprised if familiar garden favourites get a makeover. Next time the scientists have been tinkering and you find your plant has snuck down to the deed poll office, don’t despair. See it as an opportunity to understand more about other plants in its new genus and learn about where your plants come from. And if you are an old dog that can’t be taught new tricks…well just call it what you want! Every winter, thousands of us are delivered gifts of Amaryllis and compete to produce the most beautiful blooms. Does anyone care that they are actually a Hippeastrum…
For up-to-date horticultural science including name changes, subscribe to the RHS’ fantastic quarterly publication The Plant Review. Information on Salvias was gleaned from the December 2019 edition The Plant Review / RHS Gardening
Angiosperm Phylogeny Group APG – classification by consensus | Kew