Although frequently confused and sharing certain visual characteristics, arborvitae and juniper are not the same plant. Arborvitae belongs to the genus Thuja, while juniper is classified under the genus Juniperus. Both are popular evergreen trees and shrubs used extensively in landscaping across the Northern Hemisphere. This article will explain their biological relationship and provide practical methods for distinguishing between the two distinct plant types.
The Definitive Taxonomic Answer
Both genera belong to the same overarching botanical group, the Cypress family, scientifically known as Cupressaceae. This family classification signifies that they share fundamental characteristics, such as producing seeds in cones and possessing scale-like or awl-like foliage.
However, the two plants separate at the next level of classification, the genus. Arborvitae is assigned to the genus Thuja, which contains only a few species, such as the American Arborvitae (Thuja occidentalis). Juniper is placed in the much larger genus Juniperus, encompassing approximately 50 to 67 different species.
This distinction at the genus level means the plants evolved along different evolutionary paths, resulting in unique biological features and growth patterns. The classification of Thuja and Juniperus as separate genera confirms they are biologically distinct, despite belonging to the same plant family.
Distinguishing Physical Characteristics
The most reliable way to tell the two plants apart is by examining their foliage and cones. Arborvitae foliage is characteristically flattened, creating a two-dimensional, fan-like spray of growth. The leaves are small, scale-like, soft to the touch, and often overlap in four rows.
Juniper foliage is often much stiffer and sharper than arborvitae. Most junipers exhibit sharp, needle-like leaves, especially on new growth, which can feel prickly. Unlike the flattened sprays of arborvitae, juniper foliage tends to be arranged around the stem, giving branches a more three-dimensional look.
A clear distinction is found in the reproductive structures, specifically the cones. Arborvitae produces small, woody, or papery cones that are typically egg-shaped or oblong, with four to six pairs of thin scales. Arborvitae is monoecious, meaning these cones are borne on the same plant. Juniper produces female cones that have fleshy, fused scales, giving them the appearance of a blue or dark berry.
These berry-like cones are a defining feature of the Juniperus genus and are often mistaken for true fruit. Furthermore, junipers are typically dioecious, meaning the male and female cones are found on separate plants. Crushing a piece of juniper foliage often releases a distinct, sharp, resinous aroma that differs from the scent of crushed arborvitae.
Common Uses and Landscape Differences
The differing physical characteristics and ecological tolerances of Thuja and Juniperus lead to distinct uses in landscape design. Arborvitae varieties, such as the popular ‘Green Giant,’ are prized for their rapid growth rate and naturally dense, columnar, or pyramidal shape. They are the go-to choice for creating tall, uniform privacy screens, hedges, and windbreaks.
Arborvitae generally prefers moist, well-drained soil and will tolerate slightly boggy conditions, often thriving in sites with slightly more alkaline soil. These plants are also known for maintaining a relatively neat form, requiring less frequent pruning than many juniper varieties.
In contrast, the juniper genus offers a much wider range of growth habits, from tall, narrow trees to low, ground-hugging shrubs. Junipers are frequently utilized for erosion control on slopes or as low-maintenance groundcover due to their ability to spread horizontally. They are also highly valued for their superior tolerance of dry, rocky, or poor soil conditions, making them excellent choices for arid or exposed landscapes.
While some columnar junipers are suitable for screens, the genus as a whole is better known for its adaptability and hardiness in bright, sunny, and drought-prone locations. This preference for drier, sunnier sites and its varied forms allows juniper to fill landscape niches that arborvitae cannot.