Members of the grass family usually do not develop woody tissue, and die down at the end of a growing season. Grasses are monocotyledonous, a characteristic that is the basis for the development of glyphosate herbicides. One leaf sprouts from the seed; grasses have jointed, slender, sheathed leaves. They can be large or small and have erect or spreading growth habit. In addition to forages, grasses are important soil conservation tools; some are used as biomass fuels.
Optimal growth temperature is an important species selection characteristic. Grasses are classified into cool-season and warm-season types, with optimal growth temperature being 22° and 30° C (72° and 86° F), respectively.
Another important characteristic of grasses is their regrowth habit: culmed or culmless. Culmed types raise their apical meristem (growing points) during each regrowth cycle, making them more susceptible to ill-timed defoliation and typically less well suited to grazing. By contrast, culmless types have only leaf material in regrowth cycles. See Grass Growth and Regrowth for Improved Management for additional information.
Legumes bear pods containing one or many seeds that are released from the pod as it ruptures. Leguminous plant roots host nodule-forming bacteria that can fix atmospheric nitrogen into plant-available nitrogen. Whether used as a forage or a seed, legumes are a source of protein-rich food. Legumes are useful cover and green manure crops, improve soil structure, and improve forage quality when seeded with grasses. Legumes have a narrower range of soil suitability conditions than grasses, in part because of the conditions required by the nodule-forming bacteria. As with grasses, legumes are grouped into cool-season and warm-season types based on their optimal growth temperature.
Forbs are herbaceous, broadleaf plants. All legumes are forbs, but not all forbs are legumes. Species from several plant families are used for forage, with the mustards, and the cabbage family prominently represented. In recent decades, plantain (Plantago lanceolata L.) and chicory (Cichorium intybus L.) have gained popularity in pasture mixes (Labreveux et al., 2006). Forbs add diversity to pastures; once animals become accustomed to them, they are consumed readily. Some are deep-rooted and absorb minerals in different proportions than grasses and legumes.