What in the forb is that?

Despite first appearances, our prairies aren’t just made of grass. There’s much more out there on the wide-open plains. Broadly, prairie vegetation falls into four categories: grasses, sedges, rushes, and forbs. So, how do you tell what’s what?

Grasses

For most of us, the term “grass” brings up images of bright green lawns cut short. But grasses are an unbelievably diverse family of plants — even corn is a species of grass — so drilling down to key characteristics used for identification is tough. This explanation focuses on generalities.

Since most prairies aren’t mowed (unless it’s a new planting or is being maintained through a grazing program) prairie grass grows much taller — up to 8 feet for some species. They’re also bunchgrasses. A bunchgrass grows as a group of stems together clumped together rather than evenly-spaced, single stems.

Each of those stems is hollow and either flat or circular. Leaves grow on two sides of the stem, alternating as the grass grows upward. Grass leaves are long and pointy. They can be identified in two parts. The top half of the leaf, hanging off the plant, is called the blade. The bottom of a grass leaf, aptly named the sheath, wraps tightly around the stem. Each of these sheaths grows from a solid, swollen-looking spot on the stem called a node. Paying attention to how the blade, sheath and nodes are formed can help you identify the species.

Sedges and Rushes

Here’s where it gets tricky. Sedges are grass-like, but they aren’t grass. The leaves of a sedge are very similar to grass leaves — they also have blades and sheaths. However, sedge leaves grow on three sides of the plant in a spiral pattern. Stems can also help people tell grass and sedges apart. Sedge stems do not have any nodes. While grass stems are hollow and circular or flat, sedge stems tend to be solid and triangular — you’ll feel the edges of the triangle if you roll the stem between your fingers.

Rushes are water-loving species and can be found in wet prairies. Rushes are also grass-like, and like sedges do not have nodes, BUT, like grasses, their stems are round. Confusing right?

To add to the identification difficulty, grasses, sedges and rushes are wind-pollinated. They don’t need showy petals to attract bees and other pollinators. With small flowers in shades of yellow, green, white and brown, these plants tend to blend together, rather than standing out with bright, distinct colors and shapes and giving us fewer clues for helpful ID.

But a simple phrase about stem differences can at least guide you to the basics: “Sedges have edges, rushes are round, and grasses have nodes from the top to the ground.”

Forbs

Speaking broadly, forbs are the plants people call wildflowers on prairie hikes. Compared to grasses, sedges and rushes, forbs’ flowers are dazzling. Forb flowers vary in size, shape and color. There are purple coneflowers with thin, droopy petals, goldenrod with its bright yellow flowers growing in long tuft-like arrangements and dozens upon dozens more.

Forbs are also broad-leaved plants — their leaves are literally broad and wide. This is very helpful for telling the difference between forbs and grasses or sedges if the plant isn’t in bloom. Grasses, sedges and rushes all have very similar leaves. In contrast, the leaf shapes and appearances on forbs can vary widely. No matter the variation, though, they won’t take on the long, pointy appearance of grass and sedge leaves.

 

Want to take a deeper dive into prairie plant identification? You might find this digitized version of a popular field guide helpful if you just want to generally browse prairie plant species found in Iowa, and this resource gets into more specifics on grass identification.