English Lavender is botanically known as Lavandula angustifolia (angustifolia meaning 'narrow leaf').
A member of the Lavandula genus, it is related to 39 species and three other sub-genera – Lavandula, Fabricia and Sabaudia.
Other lavender species that belong to the Lavandula group include Spanish Lavender (Lavandula stoechas) and French Lavender (Lavandula dentata).
English Lavender goes by several different common names such as True Lavender, Common Lavender, Fine Lavender and Narrow-leaved Lavender. It belongs to the Mint family (Lamiaceae) and is a relative of popular garden herbs, such as Thyme, Sage and Rosemary. An endemic plant of the Mediterranean region, it is native to southern France and northern Spain.
Credit: Tomasz J KÅ‚ossowski
English Lavender has been a medicinal herb that has been featured in editions of the British Pharmacopoeia for over 200 years. Once common place in many households, it was considered an effective remedy for use in emergencies and lingering ailments.
Its historic uses are wide and varied, and were described in the 1800s by Culpeper as being "of a special good use for all the griefs and pains of the head and brain that proceed a cold cause, as the apoplexy, falling sickness, the dropsy, or sluggish malady, cramps, convulsions, palsies and other faintings.” 
This medicinal herb is known for its volatile oil that includes the constituents of linalol, cineole, limonene, linalyl acetate, geraniol, and sesquiterpenes.  Other chemical compounds are coumarin, tannin, saponin and ethereal compound. 
The constituents of lavender oil usually fall into the following range:
• Linalool 29 46%
• Linalyl Acetate 36 51%
• 1,8-Cineol 0.1 2.2%
• Caryophyllene 2.5 7.6%
• Terpinen-4-ol 2.7 6.9%
• Ocimenes 2.5 10.8%
• Lavandulyl Acetate 3.4 6.2%
The therapeutic actions of L. angustifolia act on a range of ailments from anxiety to wounds, from headaches to joint pain and digestive upsets related to nervous tension.
English Lavender has a sedative action and is useful in promoting sleep. It is also an excellent reliever of tension, particularly when stress is a cause. English Lavender functions as a mild tonic and is restorative to the nervous system when it is exhausted.
The Dictionary of Modern Herbalism describes the herb’s actions as being “relaxant and antispasmodic; circulatory stimulant; nervous tonic” and having “applications: to nervous irritation, exhaustion and depression; digestive colic and flatulent dyspepsia; the oil used locally for headaches and arthritic pain.” 
English Lavender is recognized for its remarkable antiseptic qualities and is excellent for treating cuts, burns, abrasions and other skin conditions. “Externally the oil may be used as a stimulating liniment to help ease the aches and pains of rheumatism.” 
Credit: Sanja565658 / Wikimedia Commons / CC BY-SA 3.0 license
Cautions for use:
Contraindications associated with this herb include external application only when using the essential oil. Massage, inhalation and bathing are acceptable uses but internal consumption must be avoided.
Next article: The Healing Power of Lavender