Juniperus communis, the common juniper—also known as ground juniper (although ground juniper is often classified as var. depress—is a wide-ranging shrub or small tree in the Cupressaceae (cypress family) native to cool temperate areas in the Northern Hemisphere, and may have one of the widest distributions of any woody plant. It is widely found in natural habitats, where its seed cones (“juniper berries”) and foliage are an important food source for numerous species of songbirds, ground-nesting birds, small mammals, and ungulate browsers, and there are dozens of horticultural cultivars for landscape and ornamental use (varying in form from spire-like to prostrate and trailing, and ranging in foliage color from blue to green to golden yellow). It is not used for timber due to its shrubby habit.
The species has complex intraspecific variation, and according to one recent treatment, includes 7 major varieties: 3 in North America; 2 in northern Europe; and 1 in Japan. Some varieties, however, have very restricted habitat and distribution—for example, var. charlottensis occurs on Queen Charlotte island in British Columbia, Canada, in nearby Alaskan islands, and on adjacent parts of the British Columbia and Alaskan coasts—and are threatened by habitat degradation.
Within North America, the ground juniper (var. depressa) is the most wide-ranging, extending through the northeastern U.S. and across much of Canada into Alaska, as well as extending south into the Rocky Mountains. It tends to grow well in disturbed areas, so its distribution has expanded during the past century.
Juniperus communis is a shrub or small tree has variable growth form, ranging from a low, spreading or upright shrub to a small tree, usually to 5 m (16.25 ft,) tall, but occasionally reaching heights up to 10 m (33 feet). Its leaves are sharp, needle-like but somewhat flattened, and ternate (occurring in threes), with a single white stomatal band on the upper side and a slight keel (ridge) on the underside. The species is dioecious—male and wind-pollinated female flowers grow on separate plants, and only female flowers develop seed cones, which have fused scales and are round and berry-like, up to 1 cm (0.5 in) in diameter. Seed cones ripen to blue or black with a glaucous (waxy) coating, and typically contain 3 to 6 seeds.
The seed cones of various Juniperus species make up 2 to 5% of the diet of 66 species of North American mammals, and are also edible by humans—they add the characteristic flavor to gin, and they are featured in teas and herbal supplements. The species is often bird-dispersed, as seed germination rates may be higher following passage through a bird gut.
(Adams 2008, Bailey et al. 1976, Martin et al. 1951, Royal Horticultural Society 2012.)