Thymus

Lemon Scented Thyme

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For many years lemon scented Thymus cultivars had been regarded as cultivars of T. × citriodorus; Thymus × citriodorus (Pers.) Schreb. in Schweigg. and Koerte, Fl. Erlang. 2: 17. 1811. (T. pulegioides × T. vulgaris).  In the Golden Thyme DNA Study in 1999, Dr. Madan Thangavelu and I demonstrated that
T. pulegioides, T. vulgaris and T. citriodorus hort. are distinct taxa and that the golden leaved cultivars, such as 'Archer's Gold', 'Aureus', 'Bertram Anderson' and 'Golden Dwarf' should be regarded as cultivars of
T. pulegioides.

Thymus pulegioides 'Bertram Anderson'

In 2003 Graham Walters of the Alpine Unit, Royal Botanic Gardens, Kew and I first looked at the citations of Persoon and Schreber (1811) and discovered to our surprise that there was no reference to hybrid status in either citation.  Persoon in 1806 described
T. serpyllum citriodorum and Schreber in 1811 described T. citriodorus.  Subsequent research has revealed that both Persoon and Schreber cited earlier authors, who had described lemon scented 
T. pulegioides and not the bushy mid green leaved, lemon scented thyme, available from garden centres and nurseries, together with its cultivars such as
T. 'Golden King' and T. 'Golden Queen'.  When Persoon described T. serpyllum citriodorum he was actually using the common name for T. pulegioides, Serpyllum, as used by Parkinson and other authors, for the lemon scented T. pulegioides.  I am very grateful to Dr. Brent Elliott for his assistance in sourcing the books in the Lindley Library upon which Persoon and Schreber based their citations.

Thymus 'Golden Queen'

Thymus 'Golden Queen'

The hybrid status arose in 1924 when Ronniger, describing native British thymes, referred to T. citriodorus as a hybrid between T. pulegioides and T. vulgaris, but only known as cultivated plants in England.  The thyme Ronniger was describing was the lemon scented garden thyme of unknown parentage and not the lemon scented
T. pulegioides of Persoon and Schreber.

In 2009 I proposed that the epithet citriodorus should be regarded as a synonym of T. pulegioides and I renamed the bush mid green leaved, lemon scented thyme T. 'Culinary Lemon'; first published in Plant Heritage, Spring 2009.  I also proposed that the golden variegated cultivars, such as T. 'Golden King', are better referred to without any specific epithet.  As far as the silver variegated cultivars are concerned, these are also better referred to without any specific epithet.  It has been confusing to have the identical looking cultivars, lemon scented 'Silver Queen' in one species and thyme scented 'Silver Posie' in another.

Thymus 'Culinary Lemon'

Thymus 'Culinary Lemon'

It would appear likely that no one in recent years has gone back to the original citations of 1806 and 1811, or to those of the earlier authors upon which Persoon and Schreber based their citations.  The problem when a mistake has been made, is that unless original data is consulted, everyone writing on a subject refers to more recent data and just perpetuates that mistake!

First published in Plant Heritage 2005 and 2009.  Click for original articles, 2005  , 2009  .

 DNA 

Updated January 2010.

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