Thyme is a widely cultivated, low-growing herb valued for its aromatic foliage and attractive appearance. As a member of the mint family, it possesses distinct physical traits that make it recognizable among other small herbs. Understanding the visual characteristics of its leaves, stems, and overall growth pattern is necessary for proper identification. Different types of thyme share a general structure but exhibit variations in color and habit.
Visual Characteristics of Thyme Leaves and Stems
The leaves of thyme are notably small, typically measuring less than half an inch (12 mm) in length. They are generally linear to oval in shape with smooth edges that often appear slightly rolled under, or revolute. The color of the foliage ranges from a gray-green to a deep, dark green, depending on the specific variety and growing conditions.
A close inspection reveals the leaves are often covered in fine hairs, giving them a slightly fuzzy or tomentose texture. These tiny leaves are densely arranged on slender stems, often appearing in tight, opposite pairs. When the new growth first emerges, the fresh stems are tender, sometimes with a reddish tint, and they release a strong herbal aroma when crushed.
Fresh, non-woody stems often feature a subtle square cross-section, a common trait of plants in the mint family. This dense foliage arrangement contributes to the plant’s compact and bushy appearance.
Understanding Thyme’s Growth Habit
Thyme is classified as a subshrub, meaning it is a low-growing perennial with a base that becomes permanently woody over time. The plant develops a thick, rigid structure at its base, from which flexible, herbaceous stems emerge each season. This woody foundation is responsible for the plant’s evergreen nature in many climates.
The way the plant grows can vary significantly, falling into two main categories: upright (mounding) or prostrate (creeping). Upright varieties, such as common thyme, form compact mounds, typically reaching a mature height of 6 to 12 inches (15 to 30 cm). The stems of these upright types angle outward and branch densely, creating a bushy, shrubby appearance.
Prostrate or creeping varieties spread horizontally, forming a dense, mat-like groundcover that often stays below 4 inches (10 cm) in height. These creeping stems sprawl outward and can root where they touch the soil, allowing the plant to spread widely.
Distinguishing Between Common Thyme Varieties
Common or English Thyme (Thymus vulgaris) is the standard culinary type, identified by its upright growth and small, solid gray-green leaves. It forms the typical compact, mounding subshrub structure.
Lemon Thyme (Thymus x citriodorus) is easily identified by its foliage, which is often a brighter green and sometimes features yellow variegation. This variety is generally more vigorous and maintains an upright, bushy growth habit, similar to common thyme. The leaves may also appear slightly larger and glossier than the standard gray-green type.
Creeping Thyme (Thymus serpyllum), sometimes called Mother of Thyme, is characterized by its dense, ground-hugging growth. It forms a low mat of tiny, dark green leaves that rarely exceed 3 inches in height, making it popular for planting between pavers. Woolly Thyme (Thymus pseudolanuginosus) is another low-growing variety, but its leaves are covered in a dense layer of fine, white hairs, giving the entire plant a silvery-gray, soft appearance.