Leaf Structure
While we are discussing vegetative tillers, let’s also take a closer look at what a leaf actually is. A leaf itself consists of a blade, a collar, and a sheath (Exhibit 5). The blade is responsible for light absorption and carbon fixation, so is critical in the photosynthesis process. The sheath connects the vascular system of the blade to the rest of the plant at nodes (Exhibit 6). The vascular system is important in transporting the photosynthetic products (sugar) to the rest of the plant, as well as bringing needed nutrients from soil to the leaf. The collar is where the blade and sheath join. (Exhibit 7).
Exhibit 5. Vegetative tiller of big bluestem (Andropogon gerardiiVitman) illustrating components of a leaf (blade, sheath, and collar). Photo credit: John Guretzky, University of Nebraska-Lincoln
Exhibit 6. Leaf sheath and collar of big bluestem (Andropogon gerardiiVitman). Photo credit: John Guretzky, University of Nebraska-Lincoln
Exhibit 7. Leaf collar of switchgrass (Panicum virgatum L.). Photo credit: John Guretzky, University of Nebraska-Lincoln
The next few images demonstrate how a collar and other characteristics, such as the presence of small hairs, can be used in identifying grass species. Switchgrass (Panicum virgatum L.), for example, has leaf blades that are for the most part glabrous, which means “hairless” (Exhibit 8). Switchgrass leaves have just a small patch of hair located at the base of the leaf blades. Also compare switchgrass to that of big bluestem (Andropogon gerardii Vitman) (Exhibit 9). You should be able to see that big bluestem contains many hairs on the leaf blades. We describe this as “pubescent.”
Exhibit 8. Leaf collar of switchgrass (Panicum virgatum L.) illustrating glabrous leaf blade with the exception of a fringe of hair above the collar. Photo credit: John Guretzky, University of Nebraska-Lincoln
Exhibit 9. Pubescent leaf blade and sheath of big bluestem (Andropogon gerardii Vitman). Photo credit: John Guretzky, University of Nebraska-Lincoln
Another identifying characteristic in leaf blades often used is the presence or absence of a ligule. A ligule is a membranous appendage found at the collar that serves as a useful trait to identify different grass species. Compare the ligule shapes of big bluestem (Exhibit 10) with that of indiangrass [Sorghastrum nutans (L.) Nash] (Exhibit 11).
Exhibit 10. Ligule, a membranous appendage at the leaf collar, on big bluestem (Andropogon gerardii Vitman). Photo credit: John Guretzky, University of Nebraska-Lincoln
Exhibit 11. Glabrous leaves and large membranous, deeply notched ligule of indiangrass [Sorghastrum nutans (L.) Nash]. Photo credit: John Guretzky, University of Nebraska-Lincoln