Further Research on Thymus citriodorus |
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Since I wrote my original article in 2005 I have done further research into the literature on Thymus citriodorus. IPNI lists Thymus citriodorus as a subspecies of T. serpyllum: Thymus serpyllum L. subsp. citriodorus Pers. Syn. Pl. (Persoon) 2(1): 130. (1806). Alternatively it is also quoted as varietas (Thymus serpyllum var. citriodorum). However at the beginning of the 19th Century neither status was yet in use. Persoon (1806) originally published the epithet citriodorus. Within T. serpyllum, Persoon (1806) detailed two elements: α lanuginosus and β citriodorus. Under the epiphet citriodorus he recognises two varieties: major and minor. As citriodorus is divided into varieties by Persoon and as it is placed under a species (T. serpyllum), botanists have given the epithet citriodorus subspecific rank and this interpretation is followed here. Under the var. major of subsp. citriodorus, Persoon (1806) refers to T. exserens Ehrh and under the var. minor he refers to T. includens Ehrh. The type of the name citriodorus must therefore be the type of either T. exserens Ehrh. ex Link (1822), or T. includens Ehrh. ex Rchb.(1831). Both these names are now regarded as synonyms of T. serpyllum. His description in Synopsis plantarum refers to older publications which describe lemon scented thymes; Florae Danicae, Vaillant's Botanicon Parisiense of 1743 and Bonelli's Sabb. Hort or Hortus Romanus. Hortus Romanus refers to Caspar Bauhin's Pinax, Tournefort's Institutiones Rei Herbariae and Tabernaemontanus's Eicones Plantarum. Lemon scented thymes in these publications are usually given the name Serpyllum foliis citri odore. Although Persoon makes no reference to any herbarium specimen, I understand that Persoon material of this taxon is held in Paris (P.), but I have not yet been able to see a copy of it. There is a microfiche in the library at Royal Botanic Gardens, Kew, but it is not indexed and so far it has not been possible to locate it within the microfiche. Schreber subsequently treated this thyme as a species: Thymus citriodorus (Persoon) Schreb. in Schweigg. and Koerte, Fl. Erlang. ii, 17 (1811). He also refers to August Bachmann's (Rivinus) Riv. mon. of 1690 and Volkamer's Flora Noribergensis of 1700. In Riv. mon. there is a description and illustration of Serpyllum citratum, which shows the growth pattern typical of T. pulegioides. Volkamer refers to Parkinson's Theatrum Botanicum of 1640. There is an illustration of Serpillum vulgare minus (ordinary mother of thyme) in Theatrum Botanicum, which shows the typical growth pattern of Thymus serpyllum; creeping stems with roots at the leaf nodes and flowering stems with spherical heads of flowers. There is also an illustration of Serpillum citratum (lemmon thyme) and this shows the typical growth pattern of T. pulegioides; a single group of roots with upright flowering stems and the typical elongated head of flowers of the species. In view of Persoon's references to older publications where the lemon thymes described and illustrated have the characteristics of T. pulegioides, in my opinion it is more likely that he is actually describing T. pulegioides and not the T. citriodorus currently available in the nursery trade. It should also be borne in mind that the common name for T. pulegioides in Germany is Serpyllum and that creeping thyme is known as Quendel and this could have led to later confusion between the species. I have been in contact with Munich Botanic Garden and they have informed me that their specimen described as T. serpyllum var. citriodorus from the herbarium Schreberianum, was identified by Jalas in 1972 as T. pulegioides L. It would appear that neither Jalas nor Morales has typified lemon scented thyme more recently. In the early 20th Century further confusion regarding species of lemon scented thymes arose because nurserymen who introduced them, wrongly placed them in the species T. citriodorus, because they smelt of lemon. Inexplicably botanists regarded T. × citriodorus and its cultivars, as cultivars within a hybrid T. × citriodorus, between T. pulegioides and T. vulgaris, because they had the characteristics of T. pulegioides. In 1924 in Fedde, Repert., Ronniger refers to T. × citriodorus in Britain. Stearn, In 1951 in the RHS Dictionary of Gardening and Bean, in 1980 in Trees and Shrubs Hardy in the British Isles, both describe cultivars of T. × citriodorus. Ronniger considered that the only examples of T. × citriodorus available in Britain were cultivated garden plants and at that time the cultivars 'Aureus' and 'Golden Dwarf' were both available from nurseries. It should be noted however that these lemon scented thymes are actually cultivars of T. pulegioides and not T. × citriodorus and the Golden Thyme DNA Study demonstrated that these lemon scented thymes should correctly be placed in the species T. pulegioides. We also demonstrated that thymes commonly grown as T. citriodorus and its cultivars are a distinct species from T. pulegioides and T. vulgaris. This confusion clearly demonstrates the importance, when determining correct attribution and appropriate status, of using several methods of delineation. This involves assessing the general characteristics of the sample, keying it out using a botanical key and comparing its DNA with a known base line of species and then using all three results to come to a final conclusion. Dr Madan Thangavelu and I intend to repeat the Golden Thyme DNA study, using a larger number of samples when we carry out the Bushy Thyme DNA study, for which I have been awarded an RHS bursary. We will also be including the silver variegated bushy thymes within the study and I shall await the results of this study before drawing any conclusions as to where these should be assigned. The application of the name T. citriodorus (Pers.) Schreber depends on research into the types of T. exserens and T. includens. Resolution of the identity of plants grown as T. citriodorus in the nursery trade must await the critical examination of that material. [This is an unpublished article for reference which will be
modified in due course as research progresses.] References Persoon, C.H. (1806). Syn Pl. 2: 130. Petropoli: Typis Caesar. Academiae Scientiarum
Schreber, J.C.D. (1811) In Schweigg. and Koerte, Flora Erlangensis ii, 17-18. Erlangae: Apud J. J. Palm
Tabernaemontanus, J.C. (1590) Eicones Plantarum, t. 360. Frankfurt: N. Bassaeus
Parkinson, J. (1640) Theatrum Botanicum, 8. London: Thos. Cotes
Bauhin, J.J. (1650-51) Historia Plantarum Universalis, 3:270. Ebroduni
Bauhin, C. (1671) Pinax Theatri Botanici, 220. Basileae: Impensis Joannis Regis
Bachmann, A.Q. (Rivinius) (1690) Introductio generalis in rem herbarium, t.41 11. Lipsiae
Volckamer, J.G. (1700) Flora Noribergensis, 315 (381). Noribergae: Sumtibus Michaellianus: Literis Knorzianis.
Tournefort, J.P. (1719) Institutiones Rei Herbariae, 197. Parisiis: E Typographia regio
Vaillant, S. (1727) Botanicon Parisiense, 184. Leide; Amsterdam: J. & H. Verbeek; Balthazar Lakeman
Bonelli, G. (1775) Hortus Romanus, 3: t. 68-69 13. Romae: Sumptibus Bouchard et Gravier
Ronniger, K. (1924) Beiträge zur Kenntnis der Gattung Thymus L. In Fedde, Repert., 22:31
Stearn, W.T. (1951) Thymus. In The RHS Dictionary of Gardening, 1st Edition, 2108-2111, Oxford Clarendon Press Bean, W.J., (1981) Thymus. In Trees & Shrubs Hardy in the British Isles, 8th Edition Revised,
589-592, |
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