Junipers are coniferous plants in the genus Juniperus of the cypress family Cupressaceae. Depending on taxonomic viewpoint, there are between 50-67 species of juniper, widely distributed throughout the northern hemisphere, from the Arctic, south to tropical Africa in the Old World, and to the mountains of Central America in the New World.

Junipers vary in size and shape from tall trees, 20-40 m tall, to columnar or low spreading shrubs with long trailing branches. They are evergreen with either needle-like and/or scale-like leaves. They can be either monoecious or dioecious. The female seed cones are very distinctive, with fleshy, fruit-like coalescing scales which fuse together to form a "berry"-like structure, 4-27 mm long, with 1-12 unwinged, hard-shelled seeds. In some species these "berries" are red-brown or orange but in most they are blue; they are often aromatic (for their use as a spice, see juniper berry). The seed maturation time varies between species from 6-18 months after pollination. The male cones are similar to those of other Cupressaceae, with 6-20 scales; most shed their pollen in early spring, but some species pollinate in the autumn.

Many junipers (e.g. J. chinensis, J. virginiana) have two types of leaves: seedlings and some twigs of older trees have needle-like leaves 5-25 mm long; and the leaves on mature plants are (mostly) tiny (2-4 mm long), overlapping and scale-like. When juvenile foliage occurs on mature plants, it is most often found on shaded shoots, with adult foliage in full sunlight. Leaves on fast-growing 'whip' shoots are often intermediate between juvenile and adult.

In some species (e.g. J. communis, J. squamata), all the foliage is of the juvenile needle-like type, with no scale leaves. In some of these (e.g. J. communis), the needles are jointed at the base, in others (e.g. J. squamata), the needles merge smoothly with the stem, not jointed.

The needle-leaves of junipers are hard and sharp, making the juvenile foliage very prickly to handle. This can be a valuable identification feature in seedlings, as the otherwise very similar juvenile foliage of cypresses (Cupressus, Chamaecyparis) and other related genera is soft and not prickly.

Juniper is the exclusive food plant of the larvae of some Lepidoptera species including Bucculatrix inusitata and Juniper Carpet and is also eaten by the larvae of other Lepidoptera species such as Chionodes electella, Chionodes viduella, Juniper Pug and Pine Beauty.

Cultivation and uses

Many of the earliest prehistoric people lived in or near juniper forests which furnished them food, fuel, and wood for shelter or utensils. Many species, such as J. chinensis (Chinese Juniper) from eastern Asia, are extensively used in landscaping and horticulture, and as one of the most popular species of bonsai. It is also a symbol of longevity.

Juniper berries are used in the distillation of gin and Jenever and the brewing of sahti. Juniper was also occasionally used in gruit, a mix of herbs used for flavouring beer prior to the use of hops.

Some junipers are susceptible to Gymnosporangium rust disease, and can be a serious problem for those people growing apple trees, the alternate host of the disease.

Some junipers are sometimes misleadingly called cedars, correctly the vernacular name for species in the genus Cedrus, family Pinaceae.