Ferns Afloat

Photo by Le.Loup.Gris licensed under CC BY-SA 3.0

My introduction to the genus Salvinia was as an oddball aquarium plant floating in a display tank at the local pet store. I knew nothing about plants at the time but I found it to be rather charming nonetheless. Every time the green raft of leaves floated under the filter outlet, water droplets would bead off them like water off of a ducks back. Even more attractive were the upside down forest of "roots" which were actively sheltering a bunch of baby guppies. 

I grew some Salvinia for a few years before my interest in maintaining aquariums faded. I had forgotten about them for quite some time. Much later as I was diving into the wild world of botany, I started revisiting some of the plants that I had grown in various aquariums to learn more about them. It wasn't long before the memory of Salvinia returned. A quick search revealed something astonishing. Salvinia are not flowering plants. They are ferns! 

The genus Salvinia is wide spread. They can be found growing naturally throughout North, Central, and South America, the West Indies, Europe, Africa, and Madagascar. Sadly, because of their popularity as aquarium and pond plants, a few species have become extremely aggressive invaders in many water ways. More on that in a bit. 

Salvinia comprises roughly 12 different species. Of these, at least 4 are suspected to be naturally occurring hybrids. As you have probably already gathered, these ferns live out their entire lives as floating aquatic plants. Their most obvious feature are the pairs of fuzzy green leaves borne on tiny branching stems. These leaves are covered in trichomes that repel water, thus keeping them dry despite their aquatic habit. 

These are not roots! Photo by Carassiuslike licensed under CC BY-SA 4.0

Less obvious are the other types of leaves these ferns produce. What looks like roots dangling below the water's surface are actually highly specialized, finely dissected leaves! I was super shocked to learn this and to be honest, it makes me appreciate these odd little ferns even more. It is on those underwater leaves that the spores are produced. Specialized structures called sporocarps form like tiny nodules on the tips of the leaf hairs.

Sporocarps come in two sizes, each producing its own kind of spore. Large sporocarps produce megaspores while the smaller sporocarps produce microspores. This reproductive strategy is called heterospory. Microspores germinate into gametophytes containing male sex organs or "antheridia," whereas the megaspores develop into gametophytes containing female sex organs or "archegonia." 

As I mentioned above, some species of Salvinia have become aggressive invaders, especially in tropical and sub-tropical water ways. Original introductions were likely via plants released from aquariums and ponds but their small spores and vegetative growth habit means new introductions occur all too easily. Left unchecked, invasive Salvinia can form impenetrable mats that completely cover entire bodies of water and can be upwards of 2 feet thick!

Sporocarps galore! Photo by Kenraiz licensed under CC BY-SA 4.0

Lots of work has been done to find a cost effective way to control invasive Salvinia populations. A tiny weevil known scientifically as Cyrtobagous singularis has been used with great success in places like Australia. Still, the best way to fight invasive species is to prevent them from spreading into new areas. Check your boots, check your boats, and never ever dump your aquarium or pond plants into local water ways. Provided you pay attention, Salvinia are rather fascinating plants that really break the mold as far as most ferns are concerned. 

Photo Credits: [1] [2] [3]

Further Reading: [1] [2] [3]

Aquarium Banana

One of my first true passions in life was maintaining freshwater aquariums. There is something about being able to observe a world totally foreign to our own that drew me in. It wasn't long before I discovered the splendor of planted aquascapes. I would have to say that my first foray into this realm probably planted the botanical seed that would later explode into the obsession it is today. 

I was always rather perplexed by a plant that I would see for sale at the local aquarium shop. They were labelled as "banana plants" because of their peculiar root structures. They never seemed to fit my aesthetic in those early days so I largely passed them by. Recently I have gotten back into aquariums, only this time it is very plant centric. While perusing the plants offered here in town, I again came across the peculiar banana plant. 

This time around, I am a bit more versed in taxonomy and this plant made more sense. I realized that the banana plants we see for sale for aquariums are small, immature specimens of some sort of "lily pad." A deeper investigation would prove me correct. Though not a true water lily (family Nymphaeaceae), the banana plants nonetheless take on a similar growth form with large, floating leaves emerging from an underwater rootstock. 

Banana plants are known scientifically as Nymphoides aquatica. Their generic name comes from their striking similarity to the afore mentioned water lilies. However, this resemblance is merely superficial. Banana plants belong to the family Menyanthaceae, making it a relative of plants like buckbean (Menyanthes trifoliata). They grow native in calm bodies of water throughout southeastern North America. Whereas the young leaves grow immersed, larger adult leaves eventually make their way to the surface where they float. 

Photo by Show_ryu licensed under Public Domain

From time to time, small white flowers are produced. This is when its familiar affiliation makes the most sense. This species is dioecious, though seed set is apparently sporadic. Regardless, banana plants readily reproduce vegetatively, either by fragmentation of their roots or by broken leaves settling in a spot and forming roots themselves. 

So far this is an interesting aquarium specimen. It seems to have adjusted to my aquarium rather well and it grows pretty quickly. In time I hope it performs more like it does in the wild than as a sad, stunted specimen doomed to a slow death. Only time will tell. 

Flower Pic: Show_ryu (Wikimedia Commons)

Further Reading: [1] 

Why All the Lace?

All too often, botanizing is restricted to the land. Sure, there is the occasional foray to a marsh or bog but, for the most part, relatively few plant folk like to get wet in their quests to meet new and exciting plant species. There is an entire world of aquatic plants that don't get enough credit. One such plant is Aponogeton madagascariensis, the lace plant.

Anyone into planted aquariums has undoubtedly come across this species at least once. It is kind of a holy grail of aquarium gardening. Hailing from Madagascar, this is one of the truly aquatic Aponogeton species. Though there are a few different geographic variations, they are all easily recognized by the lacy appearance of their leaves. Known as "fenestration," the lacy structure is the result of programmed cell death during the development of the leaves. As interesting as that fact is in and of itself, the question remains, what is the function of fenestration?

There have been many hypotheses put forward to explain this phenomenon. Some believe it helps to reduce damage from turbulence wheras others believe it helps to increase movement around the leaves and helps avoid stagnation. The truth is, no one is entirely certain. However, a clue to the benefits of fenestration has come out of work done on an entirely unrelated terrestrial plant species.

The epiphytic arum commonly referred to as a Swiss cheese plant (Monstera deliciosa) also exhibits fenestrated leaves. Researchers at Indiana University in Bloomington have found that the holes in the leaves may actually help gather more light in a shaded environment. The understory of a rainforest and the underwater habitat in which the lace plant grows may be more similar in light availability than you would think. How would holes in the leaves allow the plant to gather more light?

As it turns out, a fenestrated leaf can grow much larger while still maintaining the same amount of surface area. By spreading out its surface area over a larger region, a fenestrated leaf is actually more efficient at gathering what limited light is available. More work needs to be done to see if this is truly the case for the lace plant but the idea is tantalizing to say the least. Sadly, like too much of Madagascar's wildlife, the lace plant is becoming quite rare in the wild due to habitat destruction. So, the next time you come across one of these in an aquarium store, make sure to give this plant the attention it deserves. 

Further Reading: [1] [2] [3]