YARD AND GARDEN: How to differentiate between native and non-native plume grasses

A few years ago I began to notice a very tall, stately grass growing on the roadsides on my daily commute. I only seemed to find it growing in southernmost Illinois. Without any good places to pull over my car on the roadsides, I wasn't able to get a closer look.

Then one day I got an email asking questions about this mystery grass. A landowner had it blooming on their property and wanted it identified. They also wanted to know if it was native or non-native since it was growing in their pollinator fields.

This led me to explore the plume grasses, in the genus Erianthus (formerly Saccharum). In Illinois there are five species of plume grasses. Four of them are native to the state, and they are all restricted to the southernmost counties of Illinois. The fifth species is non-native and could be found throughout Illinois where it escaped from cultivation. Let's take a closer look at these grasses.

General characteristics

These grasses are robust, tall, warm-season bunchgrasses. They can grow to heights over 12 feet tall, with their inflorescences getting up to two feet tall. Their bunches can grow to five feet in diameter. They have thick stems and long, tapering leaves. They bloom in the fall.

Which one isn't like the others?

Ravenna grass, or hardy pampas grass, Erianthus ravennae, is the non-native plume grass found in Illinois. The easiest way to tell it apart from the other grasses is to measure the awns (stiff, bristle-like structures that emerge from the tip of the spikelet) of the spikelets (flowering units) when it is in bloom. This grass has awns under 6mm in size, while the other plume grasses have awns over 10mm in length.

This grass is not recommended for planting because of its invasive potential. A possible replacement with a similar look, although smaller in size, is Indian grass. It produces plume-like inflorescences and has a bunchgrass form.

The native plume grasses

This year I noticed that we had one bunch of plume grass growing behind our office. I went out and tried to identify it, and I ended up with two options: either sugarcane plume grass, Erianthus giganteus or silver plume grass, Erianthus alopecuroides. These grasses are nearly identical in their characteristics.

This grass towered over me, easily 10 feet tall in bloom. Its leaves are over two feet long and about an inch wide, with a prominent midrib. On the tops of the leaves near the base you can find coarse hairs. There is a hairy ligule at the base of the leaf blade where it becomes the sheath and wraps around the stem. The inflorescence (flowering cluster) is a branched panicle over a foot in size. The bottom of the stem under the panicle is covered in silky hairs. The spikelets (flowering units) are surrounded by soft hairs.

There are two main diagnostic differences between these two species of plume grasses are:

Where did this leave me? At first I wrote this saying that this was sugarcane plume grass. But over the past couple of days, the awns on the spikelets I brought inside and set on my desk slowly started to twist. There's no denying the twist of the awns, so I have to change my mind and go with silver plume grass. Now, does the species in this case really matter? This might be a case where discovering you have the native species and not the non-native one might have been enough for you. Or you could want the final answer like I did. Remember I still had two other options. The four native plume grasses have some differences between them in hairiness of the flowering stems under the inflorescences, twistiness of the awns, and width of the leaves, which allowed me to eliminate the other two much more quickly.

Need a refresher on grass identification terms? Check out extension.illinois.edu/blogs/grasses-glance

This week's recipe roundup features meals that are heavy on fruit and veggies, but still quick and easy to make.

Illinois Extension leads public outreach for University of Illinois by translating research into action plans that allow Illinois families, businesses, and community leaders to solve problems, make informed decisions, and adapt to changes and opportunities.