It’s difficult to overstate the importance of turfgrass managers being able to correctly identify the grasses they maintain. From basic management recommendations to differences in pesticide tolerance, knowing the type(s) of turfgrass you manage is critical to your success.
For those just starting out in the industry, properly identifying turfgrasses may seem challenging, since the individual plants and the structures used to identify them can be quite small in a managed turfgrass setting. The most obvious complicating factor is that we mow these grasses, making the plant smaller and preventing and/or removing the inflorescences (as illustrated in Figure 1), which botanists consider the most useful structure to aid in grass identification.
Figure 1. The inflorescence, when available, is the best structure upon which to base your grass identification. For example, Kentucky bluegrass and perennial ryegrass can be confused based on morphological features. However, the differences between the seed head of bluegrass (a panicle) and ryegrass (a spike) are pretty obvious.
For example, take Kentucky bluegrass and perennial ryegrass, which are often confused. Hopefully after reading this article you will agree with me that these two species really should never be confused. There’s the difference in their morphological structures, but even more obvious is the difference in the appearance of their seed heads. If present, the seed head should definitely be utilized when identifying a grass.
The crown and roots are of no value in identifying a grass. However, other structures can be useful for identification. Following is a brief description of each of these structures, and they are illustrated in Figure 2.
Ligule: An appendage at the upper junction of blade and sheath. In all but a few cases, the ligule is a membrane on cool-season grasses and a fringe of hairs on warm-season grasses. The only exceptions to this in turfgrasses are the paspalums, which have a membrane and fringe of hairs. This is the first structure I look at when identifying a grass. For example, centipedegrass (a warm-season species) has a distinct ligule that looks like a piece of cotton. Creeping bentgrass and annual bluegrass both have distinct membranous ligules.
Figure 2. Variations on structures used to identify turfgrasses.
PHOTOS COURTESY OF DAVE GARDNER
Vernation: The leaf arrangement in the bud shoot. When they are emerging, leaves may either unroll or unfold. Take a relatively young leaf, pinch it off halfway down its growth, and then look at it from the top. If it is V-shaped then it has folded vernation. If it is comma shaped it is rolled vernation. About half of the cool-season grasses have rolled vernation and half are folded. Among warm-season grasses, the panicoid grasses (St. Augustine grass, kikuyugrass and centipede grass) are distinctly folded, while the chloridoid grasses (zoysiagrass and buffalograss) are rolled. Bermudagrass is a chloridoid grass that has both rolled and folded vernation types. This is the second structure I look at when identifying a grass. I mentioned that creeping bentgrass and annual bluegrass both have distinct membranous ligules; however, creeping bentgrass has rolled vernation and annual bluegrass is folded.
Shoots: In almost all cases the growth habit of the grass is useful information to have. If it has only tillers (lateral shoots that remain within the leaf sheath), then it is a bunch-type grass. There are two types of spreading grasses. One type has rhizomes – subsurface lateral shoots with elongating internodes, which are stem segments between nodes. The other type of spreading grass has stolons, which are similar to rhizomes, except they grow above ground and contain chlorophyll. Growth habit can be hard to determine, but is useful when picking among similar grasses. For example, creeping bentgrass has stolons, and annual bluegrass is a bunch-type grass. Among the bluegrasses, Kentucky bluegrass has rhizomes, rough bluegrass has stolons, and, as noted, annual bluegrass is a bunch-type.
Location of Structures on the Plant
The following structures are also useful, but are less universally encountered:
Auricle: Appendages that extend from the collar and wrap around the leaf. Basically, if you see distinct clasping auricles, you either have annual ryegrass or quackgrass. These can be short and stubby on tall fescue and perennial ryegrass, or slender, such as on wheatgrass.
Collar: A distinct band of tissue at the blade/sheath junction. On St. Augustine grass, and to a lesser extent centipede grass, the collar is constricted and the leaf blade twists at this point. On cool-season grasses, tall fescue has a broad, continuous collar.
Sheath: The lower part of the leaf attached to node at the crown. Most of the time it is split and overlapping. If it is a fused tube, you either have a bromegrass or an orchardgrass. The sheath of rough bluegrass is very thin, so as to look like onion skin.
Leaf tip: Usually they are pointed. The bluegrasses have a boat-shaped tip (the end looks like a canoe), and if you run this between your thumb and forefinger it will split into two halves.
Leaf blade venation: This can be coarse or smooth. Tall fescue is distinctly coarse, but so is the venation of creeping bentgrass.
Having an understanding of all of these structures and using them together provides you with a nearly 100-percent effective method of identifying grasses. So while creeping bentgrass and annual bluegrass both have distinct membranous ligules, creeping bentgrass has rolled vernation, stolons, pointed leaf tips and coarse leaf venation. Annual bluegrass, which is usually bunch-type, has folded vernation, boat-shaped leaf tips and smooth leaf venation. Thus there are four pretty easy to identify differences between those two grasses.
I tell my students to develop an approach that works for them, but that involves as many or all of the features discussed here. For example, one way to identify grasses is to simply remember all the most important features of each species, such as what is highlighted in Table 1.
Table 1: Summary of the differences among grasses in regards to structures used for identification. The most important structures are highlighted. Several characteristics should be used. When present, the inflorescence is the most reliable ID characteristic.
Another approach is to be more systematic and develop something like my taxonomic key. The key first asks you to determine what type of ligule the grass has, and then it asks you to determine what the leaf arrangement (vernation) is. After that, certain grasses can be verified using obvious clues (the auricle on annual ryegrass), or there are other questions to answer. I wrote this key in September of 1991, right after I received the only “F” of my college career on the first quiz in my introductory turfgrass science class, which covered the identification of grasses. The taxonomic key has been useful for me.