Common juniper is a gymnosperm. It is the most widely distributed woody plant on the planet. It forms a great girdle around the cool temperate regions of the northern hemisphere. Despite such a wide distribution it is locally threatened, especially in parts of the United Kingdom, through changing patterns of land use, whilst in other parts of the world it is an invasive.
Common juniper is readily recognised by the triplets of green or blue-green, wax-covered, needle-like leaves that form rings along the young stems. Unlike many members of the genus Juniperus, needle-like leaves are retained throughout the plant's life; in other Juniperus species mature plants have scale-like leaves.
Common juniper has separate male and female plants. Male plants have tiny, yellow cones that shed wind-dispersed pollen. Female plants have berry-like, fleshy seed cones that become purple-black, with a waxy bloom, on maturity. Each seed cone comprises about three fused scales, each with an associated seed. Seeds are usually bird dispersed.
Females cones are used widely as a flavouring in cooking, especially game, and most famously in flavouring gin. In 1751, the cartoonist and printmaker William Hogarth published the famous print Gin Lane, in direct support of the Gin Act; he portrayed its denizens as unhappy, feckless and lazy. Another of juniper's uses - as an abortifacient - is reflected in one of its forthright English common names, 'bastard killer'. The wood is hard, dense and highly scented but individual pieces are too small to have significant commercial value, except in certain types of decorative work. The oil is sometimes used to treat skin conditions.
Not only does common juniper have a wide geographic range, it has a wide ecological range with plants found from sea level to more than 3,000 m altitude, in habitats as diverse as coastal dunes, lowland pastures to exposed highland areas. Patterns of morphological variation are similarly diverse from small, prostrate shrubs tens of centimetres tall to trees up to 10 metres tall. Patterns of DNA variation do not mirror morphological variation, adding to the complexities of understanding the biology of common juniper. Complex variation patterns have led to numerous proposals for dividing the species into subspecies or varieties but there is little consensus.
The horticultural trade has capitalised upon the range of natural variation in common juniper to select many different named forms that are especially popular as evergreen ground cover or specimen plants.
Adams RP 2014. Junipers of the world: the genus Juniperus. Trafford.
Farjon A and Filer DF 2013. An atlas of the world's conifers. Brill.