Many species of grass naturally form dense, elevated masses rather than a continuous, spreading carpet. This clumping habit is a specific botanical strategy that influences how the plant survives, interacts with its environment, and is used in landscaping. Understanding the unique terminology and mechanisms behind this growth provides insight into the diverse world of the Poaceae family.
The Primary Terminology
The most common terms used to describe clumps of grass are “bunchgrass” and “tussock grass.” These terms refer to species that grow as singular plants in concentrated, dense tufts instead of forming a continuous sod or mat. This growth form is also described by the botanical term caespitose. Examples include California fescue (Festuca californica), deer grass (Muhlenbergia rigens), and prairie dropseed (Sporobolus heterolepis). Ornamental bunchgrasses are valued for their distinctive fountain-like shape and architectural presence in a garden.
Clumping Versus Spreading Growth Habits
The difference between clumping and spreading grasses lies in the structure of their lateral stems. Clumping grasses, such as bunchgrasses, grow primarily through a process called tillering. Tillers are new shoots that develop from buds at the base of the plant, growing vertically within the sheath of the surrounding leaves. This internal, vertical growth, known as intravaginal tillering, results in the compact, dense cluster that defines the bunchgrass form. The absence of specialized horizontal stems prevents the formation of a spreading turf.
In contrast, sod-forming or spreading grasses use specialized lateral stems to colonize new areas. These stems are called rhizomes when they grow horizontally underground and stolons when they creep along the soil surface. Both rhizomes and stolons root at their nodes, producing new, genetically identical daughter plants some distance from the parent. This mechanism allows the grass to form a continuous, interlocking mat.
Ecological and Landscaping Significance
The clumping growth habit has significant consequences for natural ecosystems. In nature, the dense, deep, fibrous root systems of tussock grasses are highly effective at stabilizing soil. Their structure helps slow water runoff and improve infiltration, which is useful for erosion control on slopes and in arid environments. These grasses also provide habitat structure for wildlife, offering cover and nesting material. Deep roots allow many bunchgrass species to access moisture from lower soil profiles, making them drought tolerant and resilient in summer-dry climates.
In a horticultural context, bunchgrasses are valued for their low-maintenance requirements compared to turf grasses. They do not require the constant edging or frequent mowing associated with spreading varieties like Bermuda grass. Landscapers use bunchgrasses as accents, for defined borders, or for large-scale restorations where a naturalistic, meadow-like look is desired.