Azolla filiculoides and additional species
Salvinia minima and more
This week’s Friday trip was displaced by a scintillating department chair meeting, two life-wasting hours dedicated to e-mailable calendar events, futile parking space rants, program enrollment statistics, personal horn-tooting, and oh-so-witty repartee. My seat-neighbors survived with sneaky smart phone activity. My phone is dumb, so I just stared out the window sullenly, dreaming of native plants and chicken marsala, and wondering what was floating on the polluted drainage ditch across the parking lot.
Upon adjournment, I checked out the ditch and found the pond scum to be largely fertilizer-fed Blue-Green Bacteria (Blue-Green “Algae”), and, better, there were little floating ferns, always fun to see. (They have their own Cyanobacteria, so stay tuned.)
In Florida we have two genera of small floating ferns: Azolla and Salvinia. Each has two Florida species, more or less, with room for debate on exactly which species are present, how they are defined, and exactly where they are native. Let’s not get into all that in our fun little blog, except to mention that the ancient Old World rice paddy species Azolla pinnata seems to have made its Florida debut right here in Palm Beach County.
Both Salvinia and Azolla float with an option of settling onto wet mud when waters recede. Both are abundant in local waters. Both come and go, almost magically, and have the capacity to go forth and multiply—to the extent of utterly covering the water surface, or clogging irrigation pumps.
Sometimes called “Waterferns” or “Mosquito Ferns,” Azollas are the smaller-statured of the two. You could mistake them at first glance for Duckweeds (that’s a different blog). A single Azolla plant can be the size of a coin, floating on the water surface with tiny branches bearing tinier leaves overlapping like shingles. Each plant has a roughly circular irregular and lumpy outline. (Azolla pinnata has an outline like a squashed conifer tree.) They can form small roots, with the absorptive root function supplemented by thin-walled hairs on the leaf surfaces.
Azolla consorts in a symbiotic relationship with Cyanobacteria (often misnomered “Blue-Green Algae”) able to fix nitrogen, that is, transform atmospheric nitrogen into fertilizer. (The German chemist Fritz Haber won a Nobel Prize in 1918 for figuring out how to do this industrially to make fertilizer and to make ammunition.) The symbiotic Cyanobacterium, Anabaena azollae, is impotent in the presence of oxygen, so the fern gives its little friends climate-controlled mucilage-lined gas chambers in hollow cavities in the leaves. Anyone with a microscope can break the fern apart with a needle in a drop of water and see the Anabaena dramatically.
Lots of plant, fungus, and animal species have one-on-one symbiotic relationships with microbes. Inquiring minds might wonder what happens to the intimate relationship when the host undergoes its sexual cycle. How do the host babies wind up with their own microbe? Different strokes for different folks, in Azolla the bacterium rides through the fern’s entire reproductive cycle. Ain’t that somethin’! Each baby Azolla has Anabaena as its birthright, sort of a trust fund baby.
A floating fern that can make fertilizer is a handy asset in a rice paddy, and Azolla has been boosting since ancient times. That’s why Azolla pinnata is sort of interesting here, even if invasive. Did it follow rice cultivation to the Agricultural Area, or just show up on its own accord? (You can imagine 100 ways for it to arrive.)
Salvinias are sometimes called Water Spangles. Our widespread Water Spangle is the Invasive Exotic Salvinia minima, perhaps enjoying a little Global Warming and inching northward. This Tropical American native has spawned reports across the southern U.S. with cameo appearances in northern states. (Taxonomic-nomenclatural confusion and easy mobility complicate assessment of the exact distribution.) It can turn a canal into a green lawn, as I saw recently in Riverbend Park in Jupiter.
Salvinia is easy to recognize. The leaves are in whorls of three. Two leaves are identical, nearly circular in outline, about a centimeter in diameter. (The leaves are larger in S. molesta , which has a couple reports in Florida, but not in our haunts so far.) The third leaf in the whorl looks like a brushy branchy root dangling in the water. The two round green leaves have unwettable surfaces with extreme hairs. In S. minima the hairs look like a scary Halloween tree; in S. molesta the hairs look like an eggbeater.
Don’t look for spores as encountered under the fronds in most ferns. Both Azolla and Salvinia have a special adaptation to the boating life— spores in little hard cases called “sporocarps.”
I have a personal theory that pond scum is going to save the world. What grows faster? Scarfs up pollutants in the process? And utilizes bad carbon dioxide? We’re talking biofuels, and even food. This video will give an idea how fast Azolla can grow —just toss in a little cow dung slurry—and feed the world! (Or at least feed the livestock.) CLICK