Juniperus communis, the Common Juniper, is a species in the genus Juniperus, in the family Cupressaceae. It has the largest range of any woody plant, throughout the cool temperate Northern Hemisphere from the Arctic south in mountains to around 30°N latitude in North America, Europe and Asia.
It is a shrub or small tree, very variable and often a low spreading shrub, but occasionally reaching 10 m tall. Common Juniper has needle-like leaves in whorls of three; the leaves are green, with a single white stomatal band on the inner surface. It is dioecious, with male and female cones on separate plants, which are wind pollinated. The seed cones are berry-like, green ripening in 18 months to purple-black with a blue waxy coating; they are spherical, 4–12 mm diameter, and usually have three (occasionally six) fused scales, each scale with a single seed. The seeds are dispersed when birds eat the cones, digesting the fleshy scales and passing the hard seeds in their droppings. The male cones are yellow, 2–3 mm long, and fall soon after shedding their pollen in March–April.
As to be expected from the wide range, it is very variable, with several infraspecific taxa; delimitation between the taxa is still uncertain, with genetic data not matching morphological data well.
Some botanists treat subsp. alpina at the lower rank of variety, in which case the correct name is Juniperus communis var. saxatilis Pallas, though the name Juniperus communis var. montana is also occasionally cited; others, primarily in eastern Europe and Russia, sometimes treat it as a distinct species J. sibirica Burgsd. (syn. J. nana Willd., J. alpina S.F.Gray).
Juniperus communis is one of Ireland's longest established plants.
It is commonly used in horticulture as an ornamental shrub, but is too small to have any general wood usage. In Scandinavia, however, juniper wood is used for making containers for storing small quantities of dairy products such as butter and cheese, and also for making wooden butter knives.
Its astringent blue-black seed cones, commonly known as "juniper berries", are too bitter to eat raw and are usually sold dried and used to flavour meats, sauces, and stuffings. They are generally crushed before use to release their flavour. The cones are used to flavour gin. In fact, the word 'gin' is derived from the French word for juniper berry, genièvre, which is the name for gin in France. The Slovak national alcoholic beverage Borovička is also flavoured with juniper berry extract.
Since juniper berries have a strong taste, they should be used sparingly. They are generally used to enhance meat with a strong flavour, such as game, including game birds, or tongue. In Finland, juniper is used as a key ingredient in making sahti, a traditional Finnish ale.
Dioscorides' De materia medica also lists juniper berries, when crushed and put on the penis or vagina before intercourse, as a contraceptive.
Juniper berries have long been used as medicine by many cultures. Juniper berries act as a strong urinary tract disinfectant if consumed and were used by American Indians as a herbal remedy for urinary tract infections. Western tribes combined the berries of juniperus communis with Berberis root bark in a herbal tea to treat diabetes. Clinical studies have verified the effectiveness of this treatment in insulin-dependent diabetes. Compounds in these plants when combined and ingested have been shown to trigger insulin production in the bodies fat cells, as well as stabilize blood sugar levels. Native Americans also used juniper berries as a female contraceptive.