From the Contact Station January 2018

What is that red stuff on the water?

We are often questioned about the “red stuff” on the sloughs and ponds at this time of year.  What is that stuff?  It is called Mexican Water-fern, Azolla mexicana, and is also known as mosquito fern. Water-ferns are small, flat, compact, moss-like plants that float freely on the water surface, often forming extensive mats. Young plants are generally bright green, which we see develop in the summer and fall on our sloughs.  They become pink, red, or dark brown as the plant matures and when exposed to strong sunlight. This species can be found from southern British Columbia to Mexico, throughout the western US and east to Utah and the western most area of Texas.

The floating mats consist of many tiny ferns with multiple pairs of individual overlapping scale-like leaves that resemble a cedar leaf. Each plant, of one to two centimeters, may have a branching stem with several pairs of leaves, but only a single dangling root. There are no flowers or fruits produced for reproduction on these plants.  Instead, reproduction occurs by spores located in a chamber on the lower submerged leaf-lobe.  Repeated freezing of our ponds and sloughs will knock down the water-fern distribution in winter, but it come back in the spring and summer.

The water-fern is associated with a blue-green alga, which can fix needed nitrogen, something the water-fern can’t do.   In return, the water-fern provides shelter and minerals for the algae. Meanwhile, the water-fern also provides food for waterfowl and cover for small invertebrates.

Some are familiar with Duckweed, another plant that forms a mat on water.  Duckweed is in another genus and doesn’t turn red like our Mexican Water-fern does.