Rosemary becomes a sage

The popular evergreen shrub and herb rosemary recently underwent a name change as genetic science more accurately identifies its relationships.

At a meeting in 2019, members of the RHS Nomenclature and Taxonomy Advisory Group accepted the move to absorb Rosmarinus into the genus Salvia.

John David, RHS Head of Horticultural Taxonomy, recognised the popularity of
the plant meant the name change may not be well received.

‘We understand everyone involved in gardening finds name changes difficult, especially when they relate to popular and widely grown garden plants such as rosemary. However, we cannot ignore what science is telling us, and clarity on a plant’s DNA helps us better understand its growth habits and cultural needs. Home gardeners should not be alarmed, as usage of “rosemary” as the common name will remain.’
 

Disentangling taxonomy

There are good botanical arguments for knowing the exact relationships between plants – for example, it can help to predict to which pest and diseases certain plants may be susceptible, now and in the future.

Another genus absorbed into Salvia is Perovskia (Russian sage), a close relative of rosemary that is also a host of the pest rosemary beetle. The most commonly grown species, Perovskia atriplicifolia, will become Salvia yangii.

Writing in the December 2019 edition of The Plant Review, Alan Paton, Head of Collections at Royal Botanic Gardens, Kew, explains that once armed with the new genetic information, botanists had three choices:
 

1. To do nothing, which would not help with further study and use
2. Continue to recognise rosemary as a genus, which would mean changing the names of more than 700 species of Salvia (many of which are popular garden plants)
3. Absorb rosemary into Salvia as a subgenus. This third choice results in only 15 name changes – rosemary and Russian sage being the most well known

The rest have limited garden appeal. Common rosemary, currently listed as Rosmarinus officinalis, is included in RHS Plant Finder 2020 as Salvia rosmarinus. The new names will be adopted in the results of the 2016–2019 RHS Plant Trial of rosemary.

"...clarity on a plant’s DNA helps us better understand its growth habits and cultural needs"

It is likely the change will take longer to feed through the horticulture industry.
Label manufacturers tend to print in large batches, so it may be several years
before plants on garden centre shelves are labelled Salvia rosmarinus.