Perennial ryegrass (Lolium perenne) is a cool-season turfgrass commonly used in lawns, athletic fields, and pastures due to its rapid establishment and attractive appearance. This species is often blended with other grasses, such as Kentucky bluegrass, to provide quick cover while the slower-growing varieties establish a dense stand. Identifying perennial ryegrass relies on observing specific structural details of the grass plant, particularly its leaves and how it grows.
Identifying Features of the Blade
The leaf blade of perennial ryegrass is a primary identification marker, typically dark green with a fine to moderate texture. A noticeable feature is the prominent mid-rib that runs down the center of the upper surface of the leaf. The top side of the blade is typically ribbed or deeply ridged.
In contrast, the underside of the leaf is smooth and exhibits a high degree of glossiness, making it appear shiny in the sunlight. This glossy bottom surface is a highly distinctive trait of Lolium perenne. New leaves emerging from the shoot are distinctly folded in the bud, a characteristic known as folded vernation, which helps distinguish it from grasses that have rolled vernation.
At the collar region where the blade meets the sheath, the plant possesses a short, membranous ligule, which is a thin, translucent tissue. The auricles, which are small, ear-like projections, are either rudimentary, very short, or completely absent in perennial ryegrass. The lack of prominent, clasping auricles is another feature used to identify this species.
Growth Habit and Tiller Characteristics
Perennial ryegrass is a bunch-type grass, growing in dense clumps and spreading primarily by producing new shoots, called tillers, from the base of the plant. Unlike creeping grasses such as Kentucky bluegrass, it does not produce stolons or rhizomes to spread laterally.
The plant is known for its quick germination and establishment rate, making it a popular choice for quick erosion control or temporary cover. When examining the base of the plant, the lower leaf sheath often displays a slight reddish or purplish tint. The overall plant height typically ranges from one to two feet when left unmowed, with numerous stiff, narrow leaves concentrated near the base of the plant.
Reproductive Structure
When the grass is allowed to mature and develop a seed head, its reproductive structure provides a clear means of identification. The inflorescence of perennial ryegrass is a slender, unbranched spike that can reach up to 12 inches in length. The spikelets, which contain the individual flowers, are flattened and arranged alternately along the main stem, or rachis.
A unique feature of the perennial ryegrass seed head is that the spikelets are oriented edgewise, or flat-side-on, to the central rachis. This orientation is a defining characteristic of the species. The spikelets generally lack awns, which are the bristle-like appendages extending from the seed, though some cultivars may exhibit rudimentary awns.
Distinguishing Perennial from Annual Ryegrass
Distinguishing perennial ryegrass (Lolium perenne) from annual ryegrass (Lolium multiflorum) is a common identification challenge. The most reliable distinction is the life cycle, as perennial ryegrass is a long-lived species, while annual ryegrass typically completes its life cycle in a single growing season. Annual ryegrass is generally coarser in texture and has a lighter green color compared to the darker, finer perennial type.
The presence of awns on the seeds is a major differentiator; annual ryegrass almost always features prominent awns, whereas perennial ryegrass seeds are typically awnless. Perennial ryegrass leaves are folded in the bud, while annual ryegrass leaves are rolled in the bud. Perennial ryegrass also exhibits a more pronounced glossiness on the underside of its leaf blade.