Grassy types of weeds are identified by parts of the plant, including the vernation, the ligule, the auricle, the sheath and the collar. Other identifying features are the blade and the seedhead and whether the plant has rhizomes or stolons.
Other ways to identify grassy weeds is the color of the leaf, the height, and where the weed grows. For example, a weed such as globe sedge is found in the southeastern United States and some parts of the western United States in sandy habitats that can range from dry to moist. It is a perennial plant with blades that are smooth, flat and bright green. It has a seedhead whose branches end in clusters that look like tiny globes, which gives the plant its name.
Another grassy weed, the very common fall panicgrass, is not only unsightly in a lawn but poisonous to livestock, even though birds eat the seeds. It is an annual grass that can grow to 6 feet tall. It has flat blades and leaf sheaths that are loose and smooth with dry and thin margins. It has membranous, somewhat downy ligules, and the seedhead is a panicle at the top of the main stem. Fall panicgrass grows in fresh or somewhat brackish water, but the seeds need dry land to germinate.