In my last post (on 05-13-20) an aquatic fern, red water fern (Azolla filiculoides) was presented. In addition to being physically different from our usual idea of a fern, red water fern, depending on one’s point of view, can be either beneficial or harmful. Because of red water fern’s good/bad duality, I call it a Jekyll/Hyde fern in reference to Robert Louis Stevenson’s protagonist.
On the negative (Edward Hyde) side, red water fern, particularly in eutrophic or nutrient-rich conditions, can grow unchecked forming thick mats and choking out other plants in the aquatic system. These thick red fern mats cause the underlying plants to die due to light starvation, resulting in oxygen-starved water and the death of fauna. The biological diversity of red water fern infected waters is reduced. Therefore red water fern is considered a noxious plant in these situations.
Red fern mats, which can become 30 cm thick, cause infected ponds and reservoirs to appear like solid ground. There are many reports of wild animals, cattle and other livestock walking onto these “hidden” bodies of water and drowning.
In the positive or potentially good (Henry Jekyll) view: Fifty million years ago the planet was hotter. Azolla species grew as far north as the Arctic Ocean. Fossil records show that Azolla formed thick mats across the entire ocean and onto continents, removing carbon dioxide from the atmosphere and helping to cool the earth. Currently research is being conducted on Azolla to determine if it can be used to counteract greenhouse gases.
Asian farmers, as long as 1,000 years ago, began to grow red water fern in their rice paddies to provide nutrients (particularly nitrogen) to their crops. Once the rice shoots begin to grow above the water level, red water fern is introduced. The rice plants grow above the Azolla and are not killed by the thick mats, yet the Azolla/cyanobacteria relationship provides nitrogen. Farming practices in other areas grow and harvest large quantities of red water fern to use as “green manure or fertilizer” on fields. Research is ongoing to determine the feasibility of large-scale use of Azolla as livestock and human food.
Ferns, in general, are not afflicted by insects. Fey-Wei Li at Cornell University has identified a specific gene in Azolla that gives the fern resistance to insects. This discovery has huge implications for agriculture.
As in the previous post, these red water fern (also commonly called duckweed fern) pictures were taken in February along Abbott’s Lagoon Trail in Point Reyes National Seashore (California).
Jekyll or Hyde – red water fern is an interesting plant.