What’s Going On?

Rhizomes are specialized plant structures that grow horizontally at or just below ground level. When observing a rhizomatous plant, the shoots that are visible aboveground are all connected to the main stem or rhizome. 

Florida hosts a variety of rhizomatous plants. Some native examples that you might be familiar with include saw palmetto, wiregrass, and prairie iris. Florida is also home to several nonnative rhizomatous plants, such as the invasive cogongrass.  

Why it Matters

For our native plants, rhizomes function as a powerful adaptation that aid in plant regrowth. Saw palmetto and wiregrass grow in fire-adapted upland ecosystems, and rhizomes specifically help these plants survive by providing a second line of defense against fire. Underground, rhizomes are buffered from potentially damaging heat, and even if a plant is burned aboveground, it can resprout from its rhizomes and continue to grow after fire.    

Both plants are critical in Florida’s upland ecosystems. The sprawling structure of saw palmetto plants and the berries it produces provide cover and food for numerous animals, ranging from birds and small amphibians to large mammals like deer or black bears, and its flowers have been shown to attract over 300 different insect species.

While not as vast in its impacts, wiregrass is also a key feature of upland ecosystems. It is one of the primary food sources for gopher tortoises, a threatened species, and as a fuel source it contributes substantially to the persistence and movement of low-intensity fire, which is necessary for the growth and reproduction of many other fire-adapted plants. So, rather than simply supporting one species, the rhizomatous resilience of saw palmetto and wiregrass can help support entire ecosystems. 

Prairie iris does not use its rhizomes for fire resistance, but rather to boost drought tolerance. This plant grows in colonies that are often found within ephemeral or seasonal wetlands, which experience fluctuating water levels and soil moisture content throughout the year, and at times dry up completely. When the prairie iris can only absorb limited moisture and nutrients from the soil, rhizomes function as a reservoir for these crucial components, storing and providing them for each iris stem until soil moisture increases again. 

With its brilliant purple flowers, prairie iris attracts large quantities of pollinators, and its seeds are a prominent food source for wetland birds. Extensive systems of rhizomes and roots can also contribute to water filtration by absorbing pollutants and excess nutrients.  

Unfortunately, the adaptive benefits of rhizomes are also found in some of Florida’s nonnative plants, which can contribute to invasive growth habits. Cogongrass is one of Florida’s most problematic invasive plants, and its rhizomes make up approximately 60% of its biomass, making it incredibly fire resilient.

Even if cogongrass is entirely burned aboveground, it can easily resprout from its rhizomes and continue growing following a burn, allowing it to outcompete native plants as it grows. These impacts are compounding, as cogongrass burns at much higher temperatures than Florida’s native plants, so with each burn, cogongrass becomes increasingly dominant. The greater intensity of fire caused by cogongrass can also harm or even kill larger plants and trees, eventually leading to a monoculture of cogongrass that provides very little ecological or forage benefit for wildlife. 

What You Can Do

To enhance native rhizomatous plants… 

• If your property is in an upland ecosystem, learn about implementing prescribed fire to support rhizomatous saw palmetto and wiregrass, along with other upland species. 

• Incorporate upland restoration by planting saw palmetto or wiregrass.  

• In areas that are moist seasonally or year-round, plant prairie iris for a low-maintenance and eye-catching addition to your landscape that is also environmentally beneficial. 

To manage invasive cogongrass… 

• Avoid prescribed fire in environments that already contain cogongrass in order to prevent adverse effects of fire intensity. 

• Apply an herbicide containing the active ingredients glyphosate or imazapyr in late summer or fall. Note that imazapyr is also extremely effective on hardwood shrubs and trees, including oaks and maples. If the patch of cogongrass is near any non-target hardwoods, avoid herbicides that include imazapyr. 
• Retreat every year to two years to control regrowth in persistent patches. 

Cover image by Hanley Renney.