Thymus polytrichus A. Kern. ex Borbás, Wild Thyme
Account Summary
Native, locally frequent. European boreo-temperate.
1881; Stewart, S.A.; Co Fermanagh.
Throughout the year.
Growth form and preferred habitats
This prostrate, low-growing, evergreen, mat- and occasionally carpet-forming, perennial subshrub is deep-rooting and produces creeping barren stems or runners and very short (up to 7 cm), erect, four-angled flowering ones, hairy on two opposite sides and almost hairless on the other two sides (see the helpful illustration in Stace 1997, Fig. 570). The small, dark green, leathery, elliptic leaves are covered in minute oil glands that give the plant its delightful, characteristic aromatic and culinary properties.
T. polytrichus is a plant of open, shallow, free-draining, calcareous or base-rich substrates in short, heathy pastures, dry banks, steep rocky places on mountain sides, screes and ledges. At sea level, it frequently occurs in calcareous maritime pastures, including on ant hills and on sea cliff top grass (Grime et al. 1988, 2007).
In many situations, T. polytrichus is most characteristic of soils that are droughted in summer, since its deep root system can obtain water when most other plants cannot. While it is a strict calcicole in S & E Britain, in the N & W of B & I, T. polytrichus can grow in a wider range of habitats, including in some acidic grasslands. This may reflect the cooler, wetter climate of the more northern, acidic habitats, where root penetration is more shallow (Pigott 1955). Frequency and abundance of Wild Thyme are always higher on warm, south-facing grassland slopes. Under typical T. polytrichus growing conditions, the infertility and physical severity of the environment strongly limits competition from other species and thus the established strategy of the species is categorised as being a Stress-tolerator. Despite its regeneration ability encompassing both seed and vegetative reproduction, T. polytrichus is a poor coloniser and is most characteristic of semi-natural, infertile, relatively undisturbed habitats (Grime et al. 1988, 2007).
Taxonomy and nomenclature
The genus Thymus has been in a wonderful state of taxonomic confusion and nomenclature flux for many years. As an instance of this, the Flora of Northern Ireland website lists ten previous names of this particular taxon. Nowadays, however, T. polytrichus (= T. praecox subsp. arcticus (Durand) Jalas = T. praecox auct. non Opiz = T. drucei Ronniger = T. serpyllum auct. non L.) is regarded as the only native Wild Thyme species in Ireland (Stace 1997; Parnell & Curtis 2012). Incidentally, the 4th edition of Stace's New Flora of the British Isles (2019) opts to take the name back to T. drucei, merely emphasising the fluidity of the nomenclature.
Thus the old Fermanagh record of T. serpyllum auct. non L., made by Stewart (1882), must in reality belong to this taxon, to which the current author (RSF) & RHN have now transferred it, making it the first county record.
Variation
T. polytrichus is so morphologically variable, in their Flora of B & I, Sell & Murrell (2009) recognise four varieties based on leaf size, inflorescence shape and size and the number of eglandular hairs on the leaves. They are named as follows: var. britannicus (Ronniger) P.D. Sell, var. neglectus (Ronniger) P.D. Sell, var. zetlandicus (Ronniger & Druce) P.D. Sell and var. drucei (Ronniger) P.D. Sell. In terms of distribution in B & I, var. britannicus is the most widespread form of the four. Var. neglectus seems to occur mainly in coastal areas. Var. zetlandicus occurs only in Shetland and var. drucei seems to occur in mountainous, northern areas (Sell & Murrell 2009). In Flora Europaea 3, p. 181, this species is regarded as one of five subspecies of T. praecox Opiz (J. Jalas, in: Tutin et al. 1972), this again indicating the extent of both morphological variation and taxonomic difficulty found within the genus.
Flowering reproduction
Plants flower from May or June to August. The species is gynodioecious (a term, incidentally, first coined by Charles Darwin), having separate hermaphrodite (ie perfect, bisexual) and smaller female flowers on different plants (Briggs & Walters 1997). This form of breeding system is an adaptation favouring cross-pollination, which in T. polytrichus is mainly managed by bees. However, the breeding system also allows the possibility of the hermaphrodite flowers selfing after insect pollination (Pigott 1955). It should be noted, however, that some gynodioecious species are self-incompatible, eg Plantago lanceolata (Ribwort Plantain) (Briggs & Walters 1997, p.150).
In T. polytrichus, the inflorescence is usually a tight head of few-flowered whorls; rarely it can be somewhat elongated. The calyx is clearly 2-lipped, the upper lip with three short teeth, the lower with two longer teeth, while the rose-purple corolla is nearly regular, scarcely 2-lipped. Nutlets, as usual, are four in number and are ovoid and smooth (Sell & Murrell 2009; Parnell & Curtis 2012). Nutlets (achenes or seeds) are shed from July onwards, or may be retained in the calyx overwinter. They can also sometimes form a short-term persistent soil seed bank, surviving between one and five years burial, although numerous reports suggest they are more transient than this, lasting less than one year (Thompson et al. 1997).
Vegetative reproduction
T. polytrichus does also reproduce asexually by gradually forming extensive evergreen mats or carpets of growth by long, horizontally spreading stems that root adventitiously at intervals. These long-lived, slow-growing clonal mats will eventually break up with age, forming individual, self-supporting plants. Plants growing in higher altitude, more exposed habitats may rely on vegetative reproduction more than those at lower levels, since seed production may be limited or restricted to warmer, sunnier years in mountain sites.
The ability to produce runners and grow long prostrate stems over shallow soils that provide little rooting depth is important in the colonisation of ant hills which are a frequent habitat feature in S England (King 1977). The runners are also significant in allowing colonisation of sand dune habitats, where the stems can survive at least 50 mm of burial by shifting sand and assist in the stabilisation of dune blow-outs (Pigott 1955; Grime et al. 1988, 2007).
Fermanagh occurrence
T. polytrichus is locally frequent and abundant on dry, shallow, infertile, lime-rich soils in the western half of Fermanagh, but nowadays it is completely absent elsewhere in the VC. Wild Thyme has been recorded in 47 Fermanagh tetrads, 8.9% of those in Fermanagh, but only 39 of them have post-1975 records. The isolated older record on the tetrad map lying E of Lower Lough Erne was made by Meikle and his co-workers at Crockanaver, S of Ederny in 1951, but the species has never again been seen in or near this vicinity. Elsewhere, the plant characteristically grows on dry banks, closely cropped fine-leaved pastures and in rocky places around the limestone areas of the county.
Irish occurrence
T. polytrichus has a very uneven distribution in Ireland, being very much more common at the coast. At the same time, while it is locally abundant in some inland VCs (BSBI Atlas 2), it is rare or extremely rare in other Irish counties. It has, for instance, only one or two stations in each of the following VCs: Carlow (H13), Westmeath (H23), Longford (H24), Cavan (H30), Monaghan (H32) and Armagh (H37) (Irish Topographical Botany; Booth 1979; Cen Cat Fl Ir 2; Reilly 2001). In Co Tyrone (H36), T. polytrichus has only ever been recorded on four occasions, all of them in sites that suggest probable garden origin (McNeill 2010).
British occurrence
Wild Thyme remains widespread and locally abundant over most of Britain apart from the most densely populated and developed regions. There is little evidence in the New Atlas hectad map of any significant population decline since the 1962 BSBI Atlas, except in the southern part of its range where general habitat pressures are greatest (K. Walker, in: Preston et al. 2002). Counter-acting these losses, to a certain extent, T. polytrichus displays a limited capacity to colonise quarries and other freshly available artificial habitats.
European and world occurrence
T. polytrichus is distributed across S, W & C Europe and is a member of the European boreo-temperate phytogeographical element (Sell & Murrell 2009). It is mapped as T. praecox Opiz subsp. arcticus (E. Dur.) Jalas (= T. drucei Ronniger) by Hultén & Fries (1986), as part of their Map 1612, where it is shown as occurring throughout B & I, Iceland and W & SW France to the Pyrenees.
Uses
Grieve (1931, p. 808-15) gives a lengthy but very interesting account of the medicinal uses and folklore of both Wild Thyme (as T. serpyllum L.) and Garden Thyme (as T. vulgaris L.), the latter considered an 'improved' cultivated form of Wild Thyme. Thyme apparently was not in general use as a culinary herb in ancient Greece and Rome, although it was known that bees working it produced high quality fragrant honey. It was employed by the Romans to give an aromatic flavour to cheese (Grieve 1931). Nowadays it is valued in the kitchen for flavouring stuffing, sauces, pickles, stews and soups, to name but a few uses.
The chief constituents of thyme are the phenols thymol and carvacrol. Cymene and pinene are also present in Oil of Thyme distilled from the leaves, plus small quantities of menthone, borneol and linalol.
The medicinal use is as an antiseptic, antispasmodic, tonic and carminative (ie for relieving flatulence). The pounded herb, mixed with syrup and given fresh, has been used as a safe cure for whooping cough. A similar mixture is given for catarrh and sore throat. Thyme tea was given for gastric disorders and for colic. It also promoted perspiration at the start of a cold and it was used to treat fever and febrile conditions generally (Grieve 1931). It older herbal medicine, Thyme was used to treat shortness of breath. An ointment of it was used to reduce hot swellings and to treat warts, help sciatica, gout and dullness of sight (Culpeper 1653). Gerard (1597) recommended it for sciatica, pains in the head, leprosy and the falling sickness. Thyme was also an ingredient of herb tobacco. Its essence was used in cosmetics and for embalming corpses. The dried flowers were also used like Lavender to preserve linen from insects.
Vickery (1995) augments these aspects slightly, most interestingly with respect to a correspondent's recommendation of it for retaining hair colour into old age – advice tragically obtained too late for the current author!
Names
The genus name, 'Thymus' is a Latinised form of the Greek, 'Thumon', the name given by Theophrastus and other early herbalist writers to a Mediterranean species, most probably the dwarf woody bush, Thymus capitatus (L.) Hoffmans. & Link (= Coridothymus capitatus (L.) Rchb. f.), which was perhaps used in offerings, being derived either from the Greek verb, 'thuein' meaning 'that which is included in a sacrifice' (Gilbert-Carter 1964; Grigson 1974) or, alternatively, the name may be derived from the Greek, 'thuo', meaning 'perfume' (Chicheley Plowden 1972).
The specific epithets mentioned are derived as follows; 'polytrichus' means 'many hairs'; 'praecox' is derived from the Latin 'praecoquo, meaning 'to ripen' and translates as 'early flowering'; and 'serpyllum' is derived from the old Greek name 'kerpyllos', meaning 'to creep' and probably originally applied to T. sibthorpii Benth. or another creeping wild thyme of the Mediterranean (Gilbert-Carter 1964; Johnson & Smith 1946).
Common English names for this species apart from 'Wild Thyme', include 'Thyme (Bank, Creeping or Running)', 'Hill Thyme', 'Pell-a-mountain', 'Puliall-mountain', or 'Penny Mountain' (corruptions of Serpyllum montanum, a previous botanical name for the species), 'Mother of Thyme', 'Mother Thyme' (both referring to use as a uterine herbal treatment), 'Shepherd's Thyme', 'Horse Thyme' or 'Brotherwort' (Prior 1879; Britten & Holland 1886; Grigson 1955, 1987).
Threats
None.