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Juniper is the common name for a large group of evergreen shrubs and trees belonging to genus Juniperus, in the family Cupressaceae (Cypress), order Pinales (pine). There are more than 50 species of Juniperus. They can be low creeping ground cover, broad spreading shrubs, or tall narrow trees. Both low growing and tall varieties are cultivated for ornamental purposes.

Junipers have thick, dense foliage and some species can be trimmed or sculpted to unusual shapes. Tall varieties, with their thick foliage, are quite wind resistant and are often planted in rows, as "windbreaks." Junipers grow throughout the world in many climates, from arctic regions, northern temperate areas, to the subtropics. Junipers are conifers, but they differ from typical cone bearing trees, which produce both male and female cones—junipers are either male or female. The female cones turn into fleshy, aromatic berries that are used for a variety of medicinal and culinary purposes. Junipers have two different types of leaves which, depending on the species, range from dark-green to a light shade of blue-gray. Some leaves are needle-like, similar to other conifers. The other type are scales that are pressed close to the twigs. Most species have a combination of the two types of leaves; young branches typically have needles, while the more mature branches have scales. Juniperus communis, or common juniper, is the one species that has only the needle type leaves.

The common juniper is a variable species, as it can occur as a shrub (3-4 ft/1-1.3 m) or tall tree (30-40 ft/10-13 m). Native to Europe, it is now widely distributed in the northern temperate zones. The color, size, and shape depend on the variety, climate, and soil. The sharp leaves, 0.7-1 in (5-15 mm) long, grow in whorls of three. Small yellow (male) or blue-green (female) cones grow at the base of the leaves. The scales on the female cones grow together and develop into fleshy, aromatic, peasized berries that contain two to three seeds. The berries take about one or three years to mature and turn a dark blue-black color when ripe.

The best known use of the oil obtained from the berries is the flavoring for gin, an alcoholic beverage invented by the Dutch. The name gin is derived from jenever, the Dutch word for juniper. The berries have a strong flavor and are thought to stimulate the appetite. They are also used to flavor soft drinks, meat dishes, and condiments (they show up in jars of dill pickles). The principal medicinal use of juniper berries has been as a diuretic (an agent that promotes urination). Juniper berries can be toxic; pregnant women and people with kidney ailments should not ingest them. Poultices made of leaves and berries have been used for bruises, arthritis, and rheumatism. The berries have also been used as a substitute for pepper, and when roasted, a substitute for coffee. Fabric dyes are also obtained from the berries.

Some species such as, the Mediterranean J. thuridera and J. excelsa grow into large trees and are an important source of timber. Juniperus virginiana, also called eastern red cedar or Virginia juniper, found in the eastern United States, was used extensively for building houses in the early nineteenth century—its aromatic wood was an excellent bug repellant, particularly the bedbug. The wood for J. virginiana is also used to make high quality pencils.

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