|Lavender flowers with bracts|
Lavandula (common name lavender) is a genus of 47 known species of flowering plants in the mint family, Lamiaceae. It is native to the Old World and is found in Cape Verde and the Canary Islands, and from Europe across to northern and eastern Africa, the Mediterranean, southwest Asia to southeast India.
Many members of the genus are cultivated extensively in temperate climates as ornamental plants for garden and landscape use, for use as culinary herbs, and also commercially for the extraction of essential oils. The most widely cultivated species, Lavandula angustifolia, is often referred to as lavender, and there is a color named for the shade of the flowers of this species. Despite its use over centuries in traditional medicine and cosmetics, there is no high-quality clinical evidence that lavender has any effects on diseases or improves health.
Leaf shape is diverse across the genus. They are simple in some commonly cultivated species; in other species, they are pinnately toothed, or pinnate, sometimes multiple pinnate and dissected. In most species the leaves are covered in fine hairs or indumentum, which normally contain the essential oils.
Flowers are borne in whorls, held on spikes rising above the foliage, the spikes being branched in some species. Some species produce colored bracts at the tips of the inflorescences. The flowers may be blue, violet or lilac in the wild species, occasionally blackish purple or yellowish. The calyx is tubular. The corolla is also tubular, usually with five lobes (the upper lip often cleft, and the lower lip has two clefts).
Lavandula stoechas, L. pedunculata, and L. dentata were known in Roman times. From the Middle Ages onwards, the European species were considered two separate groups or genera, Stoechas (L. stoechas, L. pedunculata, L. dentata) and Lavandula (L. spica and L. latifolia), until Linnaeus combined them. He only recognised five species in Species Plantarum (1753), L. multifida and L. dentata (Spain) and L. stoechas and L. spica from Southern Europe. L. pedunculata was included within L. stoechas.
By 1790, L. pinnata and L. carnosa were recognised. The latter was subsequently transferred to Anisochilus. By 1826 Frédéric Charles Jean Gingins de la Sarraz listed 12 species in three sections, and by 1848 eighteen species were known.
One of the first modern major classifications was that of Dorothy Chaytor in 1937 at Kew. The six sections she proposed for 28 species still left many intermediates that could not easily be assigned. Her sections included Stoechas, Spica, Subnudae, Pterostoechas, Chaetostachys, and Dentatae. However all the major cultivated and commercial forms resided in the Stoechas and Spica sections. There were four species within Stoechas (Lavandula stoechas, L. dentata, L. viridis, and L. pedunculata) while Spica had three (L. officinalis (now L. angustifolia), L. latifolia and L. lanata). She believed that the garden varieties were hybrids between true lavender L. angustifolia and spike lavender (L. latifolia). 
In addition, there are numerous hybrids and cultivars in commercial and horticultural usage.
The first major clade corresponds to subgenus Lavandula, and the second Fabricia. The Sabaudia group is less clearly defined. Within the Lavandula clade, the subclades correspond to the existing sections, but place Dentatae separately from Stoechas, not within it. Within the Fabricia clade, the subclades correspond to Pterostoechas, Subnudae, and Chaetostachys.
Thus the current classification includes 39 species distributed across 8 sections (the original 6 of Chaytor and the two new sections of Upson and Andrews), in three subgenera (see table below). However, since lavender cross-pollinates easily, countless variations present difficulties in classification.
The English word lavender is generally thought to be derived from Old French lavandre, ultimately from the Latin lavare (to wash), referring to the use of infusions of the plants. The botanic name Lavandula as used by Linnaeus is considered to be derived from this and other European vernacular names for the plants. However it is suggested that this explanation may be apocryphal, and that the name may be derived from Latin livere, "blueish".
The names widely used for some of the species, "English lavender", "French lavender" and "Spanish lavender" are all imprecisely applied. "English lavender" is commonly used for L. angustifolia, though some references say the proper term is "Old English Lavender". The name "French lavender" may refer to either L. stoechas or to L. dentata. "Spanish lavender" may refer to L. stoechas, L. lanata or L. dentata.
The most common form in cultivation is the common or English lavender Lavandula angustifolia (formerly named L. officinalis). A wide range of cultivars can be found. Other commonly grown ornamental species are L. stoechas, L. dentata, and L. multifida (Egyptian lavender).
Because the cultivated forms are planted in gardens worldwide, they are occasionally found growing wild as garden escapes, well beyond their natural range. Such spontaneous growth is usually harmless, but in some cases Lavandula species have become invasive. For example, in Australia, Lavandula stoechas has become a cause for concern; it occurs widely throughout the continent, and has been declared a noxious weed in Victoria since 1920. It is regarded as a weed in parts of Spain.
Lavenders flourish best in dry, well-drained, sandy or gravelly soils in full sun. English Lavender has a long germination process (14-28 days) and matures within 100-110 days. All types need little or no fertilizer and good air circulation. In areas of high humidity, root rot due to fungus infection can be a problem. Organic mulches can trap moisture around the plants' bases, encouraging root rot. Gravelly materials such as crushed rocks give better results. It grows best in soils with a pH between 6 and 8. Most lavender is hand-harvested, and harvest times vary depending on intended use.
Commercially, the plant is grown mainly for the production of lavender essential oil of lavender. English lavender (Lavandula angustifolia) yields an oil with sweet overtones, and can be used in balms, salves, perfumes, cosmetics, and topical applications. Lavandula × intermedia, also known as lavandin or Dutch lavender, yields a similar essential oil, but with higher levels of terpenes including camphor, which add a sharper overtone to the fragrance.
The lavandins Lavandula × intermedia are a class of hybrids of L. angustifolia and L. latifolia. The lavandins are widely cultivated for commercial use, since their flowers tend to be bigger than those of English lavender and the plants tend to be easier to harvest, but lavandin oil is regarded by some to be of a lower quality than that of English lavender, with a perfume less sweet.
Some 100 individual phytochemicals have been extracted from lavender oil, including major contents of linalyl acetate (30-55%), linalool (20-35%), tannins (5-10%), and caryophyllene (8%), with lesser amounts of sesquiterpenoids, perillyl alcohols, esters, oxides, ketones, cineole, camphor, beta-ocimene, limonene, caproic acid, and caryophyllene oxide. The relative amounts of these compounds vary considerably among lavender species.
Culinary lavender is usually English lavender, the most commonly used species in cooking (L. angustifolia 'Munstead'). As an aromatic, it has a sweet fragrance with lemon or citrus notes. It is used as a spice or condiment in pastas, salads and dressings, and desserts. Their buds and greens are used in teas, and their buds, processed by bees, are the essential ingredient of monofloral honey.
The potency of the lavender flowers increases with drying which necessitates more sparing use to avoid a heavy, soapy aftertaste. Chefs note to reduce by two-thirds the dry amount in recipes which call for fresh lavender buds.[better source needed]
Lavender buds can amplify both sweet and savory flavors in dishes, and are sometimes paired with sheep's-milk and goat's-milk cheeses. Lavender flowers are occasionally blended with black, green, or herbal teas. Lavender flavors baked goods and desserts, pairing especially well with chocolate. In the United States, both lavender syrup and dried lavender buds are used to make lavender scones and marshmallows.
Lavender buds are put into sugar for two weeks to allow the essential oils and fragrance to transfer; then the sugar itself is used in baking. Lavender can be used in breads where recipes call for rosemary. Lavender can be used decoratively in dishes or spirits, or as a decorative and aromatic in a glass of champagne. Lavender is used in savory dishes, giving stews and reduced sauces aromatic flair. It is also used to scent flans, custards, and sorbets.
The greens are used similarly to rosemary or combined with rosemary to flavor meat and vegetables in savory dishes. They can also be used to make a tea that is milder than teas made with the flowers.
The flowers yield abundant nectar, from which bees make a high-quality honey. Monofloral honey is produced primarily around the Mediterranean, and is marketed worldwide as a premium product. Flowers can be candied and are sometimes used as cake decorations. It is also used to make "lavender sugar".
Flower spikes are used for dried flower arrangements. The fragrant, pale purple flowers and flower buds are used in potpourris. Lavender is also used as herbal filler inside sachets used to freshen linens. Dried and sealed in pouches, lavender flowers are placed among stored items of clothing to give a fresh fragrance and to deter moths. Dried lavender flowers may be used for wedding confetti. Lavender is also used in scented waters and sachets.
The ancient Greeks called the lavender herb : nárdos, Latinized as nardus, after the Syrian city of Naarda (possibly the modern town of Dohuk, Iraq). It was also commonly called nard. The species originally grown was L. stoechas.
During Roman times, flowers were sold for 100 denarii per pound, which was about the same as a month's wages for a farm laborer, or fifty haircuts from the local barber. Its late Latin name was lavand?rius, from lavanda (things to be washed), from the verb lav?re (to wash).
Lavender was introduced into England in the 1600s. It is said that Queen Elizabeth prized a lavender conserve (jam) at her table, so lavender was produced as a jam at that time, as well as used in teas both medicinally and for its taste.
Lavender was not used in traditional southern French cooking at the turn of the 20th century. It does not appear at all in the best-known compendium of Provençal cooking, J.-B. Reboul's Cuisinière Provençale. French lambs have been allowed to graze on lavender as it is alleged to make their meat more tender and fragrant.
Despite dozens of preliminary clinical studies on the potential for lavender oil or other lavender plant components to affect human diseases, there are no confirmed anti-disease or health effects as of 2018, mainly due to the poor quality of study design and conduct.
The German scientific committee on traditional medicine, Commission E, reported uses of lavender flower in practices of herbalism, including its use for restlessness or insomnia, Roehmheld's syndrome, intestinal discomfort, and cardiovascular diseases, among others.
The U.S. National Institutes of Health (NIH) states that lavender is considered likely safe in food amounts and possibly safe in medicinal amounts. NIH does not recommend the use of lavender while pregnant or breast-feeding because of lack of knowledge of its effects. It recommends caution if young boys use lavender oil because of possible hormonal effects leading to gynecomastia caused by a genetic anomaly and tainted lavender via pesticides, and states that lavender oil may cause skin irritation and could be poisonous if consumed by mouth.
A 2007 study examined the relationship between various fragrances and photosensitivity, stating that lavender is known "to elicit cutaneous photo-toxic reactions", but does not induce photohaemolysis.
This is based on the classification of Upson and Andrews, 2004.
I. Subgenus Lavendula Upson & S.Andrews
II. Subgenus Fabricia (Adams.) Upson & S.Andrews
III. Subgenus Sabaudia (Buscal. & Muschl.) Upson & S.Andrews
Lavandula fields near Drama
'By the Greeks the name Nardus is given to Lavender, from Naarda, a city of Syria near the Euphrates, and many persons call the plant "Nard." St. Mark mentions this as Spikenard, a thing of great value. In Pliny's time, blossoms of the Nardus sold for a hundred Roman denarii (or L.3 2s. 6d.) the pound. This Lavender or Nardus was called Asarum by the Romans, because it was not used in garlands or chaplets. It was formerly believed that the asp, a dangerous kind of viper, made Lavender its habitual place of abode, so that the plant had to be approached with great caution.'
Note however that Upson and Andrews refer to research on bathing in the Roman Empire, and state that there is no mention of the use of lavender in works on this subject.
PUR FAIT YPOCRAS. XX.IX. XI. Treys Unces de canett. & iii unces de gyngeuer, spykenard de Spayn le pays dun denerer, garyngale, clowes, gylofre, poeurer long, noiez mugadez, maziozame cardemonij de chescun i quart' douce grayne & de paradys stour de queynel de chescun dim unce de toutes, soit fait powdour &c.
Also, oils of lemon, lavender, lime, sandalwood, and cedar are known to elicit cutaneous phototoxic reactions, but lavender, sandalwood, and cedar oil did not induce photohaemolysis in our assay...Lavender oil and sandalwood oil did not induce photohaemolysis in our test system. However, a few reports on photosensitivity reactions due to these substances have been published, e.g. one patient with persistent light reaction and a positive photo-patch test to sandalwood oil