Rexford Talbert shares the fruit of his 30 years of study in this exploration of thyme, it's varieties and it's history.
I've spent more than thirty years in the pursuit of thymes. How did I become so fascinated by tiny plants whose most extroverted characteristic is their fragrance? These modest herbs have captured me with their extraordinary diversity of form, coloration, and fragrance and their complex chemistry. The difficulty of identifying the hundreds of forms in the genus Thymus and of traversing the morass of names that have been attached to them has presented a challenge that I’ve found irresistible. Thymes, more than any other plants I can think of, have rewarded me with beauty, utility, and intellectual pleasure.
So I’m addicted. I will spend my days in continued obsession with growing, using, and studying this group of herbs, searching out answers to the question “What thyme is it?”
The all-too-common view of Thymus as a single species or perhaps as two, an upright and a low-growing one, belies the complexity of a genus comprising several hundred species and maybe a thousand or more forms. Analysis of the essential oils of misidentified thyme plants has led to an accumulation of confusing data and further clouded the picture of their true relationships to one another.
To approach the vast subject of thyme, one must either attempt to address the hundreds of species—which would surely outstrip my stamina as a writer and your patience as a reader—or look for its character within one species. Although the second approach is like having to choose among children or name a favorite composer of music, I’ve opted here to look at a single species: common thyme (T. vulgaris). This is the form used most often in the kitchen and in the essential oil industry and one that has claimed a place throughout history.
Fossil remains from the Tertiary period—more than 5 million years ago—show imprints of recognizable present-day thyme species. The word “thyme” in both ancient and modern times has been applied to any of various plants that have the combined flavor of thymol and carvacrol, two constituents of the essential oil. The Arabic word for thyme, za’tar, for example, designates not only a culinary mixture but also a number of different herbs, depending on where in the Eastern Mediterranean you encounter it.
A Greek root of the generic name Thymus denotes a rising cloud or vapor, which would seem appropriate for an herb that has been used as both a fumigant and incense. The Greek word thumon, “soul”, may also be a source of the word. The thymus gland, which lies behind the breastbone and plays a major role in the development of the immune system during childhood, was once thought to house the human soul.
Thyme has been used medicinally for treating a wide range of conditions, from anemia and asthma to warts and whooping cough. Today it is used most often as an antiseptic, a digestive aid, antispasmodic, astringent, nervine, and tonic. The oil has been used to treat burns, eczema, psoriasis, intestinal parasites, and ringworm, to preserve meats, and to inhibit the growth of mildew. It is a common ingredient of toothpastes and mouthwashes.
All forms of T. vulgaris are upright perennial subshrubs that typically grow to about 12 inches tall. Their leaves are green or gray, and their flowers, white to pale lavender. Although they are less versatile in the landscape than the infinitely variable creeping thymes, for example, they still deserve a place in the herb garden where they can be easily harvested for the kitchen.
T. vulgaris, a native of dry Mediterranean regions, has evolved a way of retaining moisture: its leaves curl at the edges, thus reducing the amount of leaf surface that is exposed to sunlight. On examining several forms of thyme, Linnaeus in 1753 designated curled leaf margins as a distinguishing characteristic of T. vulgaris. However, this did not prevent garden writers, later and even now, from incorrectly placing the flat-leaved ‘Broad-leaf English’ in this species when, in fact, it is a hybrid of uncertain parentage.
The arrangement of flower parts in T. vulgaris has contributed to the diversity of the genus. Common thyme can have bisexual flowers (which contain both male and female parts) or female flowers (lacking male parts or having sterile ones) on different plants or on the same plant maturing at different times. This arrangement encourages cross-pollination (and thus increased variation among the offspring), as the female flowers must receive pollen from a nearby perfect flower to enable them to produce seeds.
Probably more interesting to an herb enthusiast is the highly evolved chemical variation in the thymes. Many herb genera contain plants that have different chemical forms, or chemotypes, but otherwise identical physical characteristics; this phenomenon accounts for variations in fragrance within a species. T. vulgaris is a good example: as many as seven chemotypes have been identified in France and Spain alone. The essential oil of each chemotype is dominated by a different constituent, which shapes the character of the plant’s flavor and fragrance. This chemical polymorphism has helped T. vulgaris adapt to different environments and has extended its range. Four chemotypes of common thyme are or have been available commercially in the United States.
• T. v. ‘Narrow-leaf French’ is the classic culinary thyme. Its flavor and fragrance are due to the predominance in the essential oil of thymol, a scent that reminds me of Vicks VapoRub (which, in fact, contains thymol), and carvacrol, which people most often associate with the flavor oregano. Some people have described the fragrance of this cultivar as medicinal, but I perceive it as a sweet spiciness.
The thymol form of T. vulgaris also has been—and still is—incorrectly offered as ‘Albus’, ‘Angustifolius’, ‘Deutscher Winter’, ‘Dymian Timo O Popolino’, ‘French Summer’, ‘French White-flowered’, and ‘Greek Gray’, among other inspirations. The multiplicity of names is testament to its culinary popularity and to creative marketing. The name ‘Narrow-leaf French’ was proposed by Harriet Flannery Phillips, who analyzed its essential oil by gas chromatography in 1982 as part of her doctoral research on Thymus.
Also bearing the characteristic thymol-carvacrol scent is T. v. ‘Miniature’, a small but shapely plant that grows to a height of about 4 inches. It has been sold for years under the incorrect name of T. nitidus. It is also good for cooking.
• T. v. ‘Bittersweet’ is the chemotype dominated by carvacrol, as determined by Phillips. ‘Bittersweet’ to me has a piney fragrance with an overtone of camphor. I have yet to eat a dish with a camphor flavor that I liked, so I don’t use this thyme in cooking. I have, however, used it in various soaps and cleansers.
• T. v. ‘Orange Balsam’ also was analyzed and named by Phillips. Its predominant constituents are a-terpineol and a-terpinyl acetate. I find the fragrance of ‘Orange Balsam’ to be piney citrus, like a somewhat resinous orange peel. I use it often with fruit salads.
• T. v. ‘Fragrantissimus’ seems to have surfaced in the 1930s and was mentioned by the garden writer Louise Beebe Wilder in 1934, but it largely disappeared from the trade sometime in the 1950s and is rarely seen today. Geraniol, the scent of rose geranium, predominates in its essential oil. I would choose this cultivar to lend a floral fragrance to rice pilaf and pound cake.
Silver thyme (T. ‘Argenteus’) may be a hybrid with T. vulgaris as one of its parents. It has been variously misidentified as belonging to T. x citriodorus and T. vulgaris, among other plants. The leaf variegation, which looks silvery at a distance in sunlight, is actually pale gold. Names that have been assigned to certain forms of ‘Argenteus’ include the word “lemon”, suggesting a lemony color or scent; however, although some people claim to detect a lemon scent in ‘Argenteus’, no lemony constituent in the oil has been identified. Cultivars with silver (not golden) variegation and a distinct lemon scent do not belong to T. ‘Argenteus’.
Lemon thyme (T. x citriodorus), which is probably a hybrid between T. vulgaris and T. pulegioides, is an attractive plant with a delightful scent. Its characteristic lemon fragrance comes from two minor constituents of the essential oil. A variegated form, ‘Aureus’, is known as golden lemon thyme.
Rexford Talbert is a retired National Aeronautics and Space Administration engineer living in Williamsburg, Virginia. At one time or another, he has grown 250 different thymes of 70 to 80 species.