By: Amy Grant
Super plant or invasive weed? The mosquito fern plant has been called both. So what is a mosquito fern? The following will uncover some fascinating mosquito fern facts and leave you to be the judge.
Native to California, the mosquito fern plant, Azolla filculoides or just Azolla, is named thus due to its habitat. While the plant starts off as small as ¼ inch (0.5 cm.), mosquito fern habitat is that of a matting, aquatic plant that can double its size in a couple of days! This thick-living carpet is named mosquito fern plant because it repels mosquito attempts to lay eggs in the water. The mosquitoes may not like mosquito ferns, but the waterfowl certainly do and, in fact, this plant is an important food source for them.
This floating aquatic fern, like all ferns, propagates through spores. However, Azolla also multiplies by stem fragments, making it a prolific grower.
The plant is sometimes mistaken for duckweed, and like duckweed, mosquito fern plant is initially green. It soon turns to a reddish-brown hue as a result of excess nutrients or bright sunlight. A red or green carpet of mosquito fern is most often found in ponds or muddy banks, or in areas of standing water in streams.
The plant has a symbiotic relationship with another organism called Anabeana azollae; this organism is a nitrogen-fixing cyanobactrium. The bacterium resides safely in the fern and supplies it with the excess nitrogen it produces. This relationship has long been utilized in China and other Asian countries as a “green manure” to fertilize rice paddies. This centuries old method has been known to increase production by as much as 158%!
So far, I think you will agree that this is a “super plant.” However, for some people, there is a down side. Because mosquito plant breaks apart so easily and, thereby, reproduces rapidly, it may become a problem. When there is an excess of nutrients introduced into the pond or irrigation water, either due to runoff or erosion, mosquito plant will seemingly explode in size overnight, clogging screens and pumps. Additionally, it is said that cattle will not drink from ponds that are clogged with mosquito fern. Now this “super plant” is more an “invasive weed.”
If the mosquito fern plant is more of a thorn in your side than a boon, you can try dragging or raking the pond to rid it of the plant. Keep in mind that any broken stems will likely multiply into new plants and the problem will likely repeat itself. If you can figure out a way to mitigate the amount of runoff to lessen the nutrients entering the pond, you can slow down mosquito fern’s growth somewhat.
Of last resort is spraying Azolla with an herbicide. This isn’t highly recommended, as it only affects a small portion of the mat of fern and the resulting rotting plant can affect water quality.
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A fern (Polypodiopsida or Polypodiophyta / ˌ p ɒ l i ˌ p ɒ d i ˈ ɒ f ɪ t ə , - oʊ f aɪ t ə / ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. They differ from mosses by being vascular, i.e., having specialized tissues that conduct water and nutrients and in having life cycles in which the sporophyte is the dominant phase. Ferns have complex leaves called megaphylls, that are more complex than the microphylls of clubmosses. Most ferns are leptosporangiate ferns. They produce coiled fiddleheads that uncoil and expand into fronds. The group includes about 10,560 known extant species. Ferns are defined here in the broad sense, being all of the Polypodiopsida, comprising both the leptosporangiate (Polypodiidae) and eusporangiate ferns, the latter group including horsetails or scouring rushes, whisk ferns, marattioid ferns, and ophioglossoid ferns.
Ferns first appear in the fossil record about 360 million years ago in the middle Devonian period, but many of the current families and species did not appear until roughly 145 million years ago in the early Cretaceous, after flowering plants came to dominate many environments. The fern Osmunda claytoniana is a paramount example of evolutionary stasis paleontological evidence indicates it has remained unchanged, even at the level of fossilized nuclei and chromosomes, for at least 180 million years.
Ferns are not of major economic importance, but some are used for food, medicine, as biofertilizer, as ornamental plants and for remediating contaminated soil. They have been the subject of research for their ability to remove some chemical pollutants from the atmosphere. Some fern species, such as bracken (Pteridium aquilinum) and water fern (Azolla filiculoides) are significant weeds worldwide. Some fern genera, such as Azolla, can fix nitrogen and make a significant input to the nitrogen nutrition of rice paddies. They also play certain roles in folklore.
Water sprite grows entirely underwater and is considered a water fern. Due to its lack of a properly developed root system, it’s an excellent water purifier as it must obtain its nutrients directly from the water. Its delicate roots require two to three inches of gravel or a similar rocky substrate to anchor it down, though water sprites will also do just fine if left to float about.
A very versatile plant, water sprite grows just as well in full shade as it does in the sun, with a pH range of 6 to 8 and water temperatures between 20 and 26.6° C (68 to 80° F). Due to its fast growth rate, you’ll have to gently trim the stems, being careful not to pull at the plant as their leaves and roots are delicate. A boon of growing in the shade, however, is that this growth rate is slowed somewhat. Another important note is that water sprite should not be incorporated into ponds with goldfish, as they find these little water ferns to be quite tender and tasty.
Wonderful natural oxygenators and water purifiers, hornworts provide shade and habitat for fish while also improving water quality. They can grow equally well in either sun or full shade (provided they still get some indirect light), and are incredibly hardy, tolerant of substantial light and temperature fluctuations between 15 to 30° C (59 to 86° F). The pH should be kept between 6 and 7.5 for most species, though.
Many hornwort species can grow up to 2 feet tall, so this should be kept in mind when choosing plants as you’ll need to make sure that your pond is large enough to accommodate them. Most fish won’t be interested in eating hornworts, but more curious koi might nibble on them – their durable nature and fast growth rate, though, mean that this won’t be an issue.
While some sources list anacharis as being a sun-loving plant, this isn’t entirely true – anacharis is quite prone to getting sunburned, and is healthiest when kept in shade or indirect light rather than full sun. At most, they should be kept in partial sun, though full shade is best. You’ll know if your anacharis is getting too much sun if the leaves start to turn yellow, brown, or become slightly crispy even though they’re underwater.
Anacharis is yet another plant that provides substantial oxygenation and purification benefits, while also providing a natural food source for fish. With a fast growth rate, being munched on by fish won’t hurt this plant and will likely be appreciated as it reduces the likelihood of you having to manually trim the plant. Anacharis is a forgiving plant and tolerates a wide range of conditions but does best with temperatures between 15 to 30° C (59 to 86° F) and a pH range of 6.5 to 7.5.
Mosquito larvae are aquatic insects and, as such, play an important role in the aquatic food chain. According to Dr. Gilbert Waldbauer in "The Handy Bug Answer Book," Mosquito larvae are filter feeders that strain tiny organic particles such as unicellular algae from the water and convert them to the tissues of their own bodies, which are, in turn, eaten by fish. Mosquito larvae are, in essence, nutrient-packed snacks for fish and other aquatic animals.
In addition, while species of mosquitoes eat the carcasses of insects that drown in the water, the mosquito larvae feed on the waste products, making nutrients such as nitrogen available for the plant community to thrive. Thus, the elimination of those mosquitoes might affect plant growth in those areas.
A mosquito's role on the bottom of the food chain does not end at the larval stage. As adults, mosquitoes serve as equally nutritious meals for birds, bats, and spiders.
Mosquitoes seem to represent a considerable biomass of food for wildlife on the lower rungs of the food chain. Mosquito extinction, if it is achievable, could have an adverse effect on the ecosystem. However, many scientists suggest that the ecosystem could eventually rebound and another species could take its place in the system.
Yes and no (some introduced)
1.вЂЇ Azolla caroliniana Willd. E
Carolina mosquito fern. CT, MA, ME, NH. Still or slow-moving water of lakes, pools, swamps, and streams. Reports of this species from RI were based on a collection taken from a pond on the University of Rhode Island campusвЂ”Champlin 51 (Champlin Herb.).
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The Go Botany project is supported in part by the National Science Foundation.
Biologically, ferns are kind of like a cross between mosses or algae, and flower plants. Ferns and fern allies have a vascular system for nutrient and water transportation within the plant. They don’t however, have flowers, fruits, or seeds. Instead, ferns reproduce through spore distribution (Andre).
Ferns produce spores in tiny, one-cell thick capsules called sporangia. These sporangia generally grow in dark patches called sori on the underside of the front segment or on separate stalks. When the sporangia mature and die, wind and water disperse the spores, allowing the plant to reproduce and pass on its genes to a new plant (Andre).
Within its a lifetime, a fern plant will produce millions, sometimes even billions, of spores. Like most seeds, spores will begin to germinate in a damp surface or area. In order to germinate, they produce a prothallus— a green tissue less than half an inch long. On the underside of this prothallus, the ferns’ gametes (eggs and sperm) are produced in separate areas within the prothallus. When in a film of water, these gametes will come together on the prothallus to make an embryonic plant that will eventually develop into a fern (Andre). Because of this need for a thin film of water, ferns tend to germinate in damp, shady areas (Pinson).
When this embryonic plant begins to develop into a fern, it unfurls from the ground in a very distinct way called circinate vernation. When the new frond emerges from the rhizome, it is coiled up. It slowly unfurls from this coil, straightening and elongating as it does so. These young, coiled ferns have become known as “fiddle heads” (Key).
The basic anatomy of a fern consists of roots, a rhizome, and a frond, or more simply, roots, stem, and leaves (Key). The frond is the leafy part of the plant, made up of the stipe and the blade. The stipe, more commonly referred to as the petiole in other plants, is the stalk that connects the leafy portion to the base of the plant. The blade is the rest of the frond that contains the leafy tissue, divided on into two sides by the rachis, or extension of the stipe through the blade. The rhizome, often called the rootstock, is the underground stem system from which the leaves are produced and the wiry roots diverge downwards. Year after year, this intricate network sends up leaves, even if fronds die and drop off, making it perennial. The rhizome is attached directly to the stipe. The roots extend below the rhizome just like any other root system, gathering water and nutrients for the plant’s survival (Key).
Ferns are particularly difficult to identify because of their diverse range in leaf structure. Some ferns, like a walking fern, are simple, often lobed. Others, like the bracken fern, are compound, often several times divided. In addition to their diverse structure, ferns exist in a wide range of leaf length, from 1/16 inches long (in an azolla fern) to almost five feet long (in a bracken fern).
Within each fern species, there is generally dimorphism, or two different forms of fronds on the same plant. One type of dimorphism is where there are two different pinnae, or particular sections on the frond, that differ in accordance to whether they are fertile or sterile. The fertile pinnae is the section of the frond that contains the sporangia. It’s generally slightly different in shape and size from the sterile pinnae, which is the section of the frond that extends down to the stipe and does not contain sporangia (Key). The other type of dimorphism is where there is a distinct modified frond for the sporangia called the fertile frond. In this case, the fertile frond has a different shape and general appearance than the sterile frond, but is connected at the rhizome. The sporangia generally appear on the underside of the fertile frond, or in the case of aquatic ferns, in a highly modified leaf called a sporocarp (Key).
Ferns as a family are ancient. They were first found nearly 400 million years ago, and there are around 12,000 species worldwide (Andre).
They can be found in a wide range of habitats, but most commonly in shady, moist areas due to their need for a thin film of water for germination. They can even be found on or at the base of trees. Ferns and fern allies derive from several different geographic origins, such as northern forests, drier regions of the southwest, moist tropical forests of central America and the Caribbean. The habitat in which each species thrives often gives indication for where it originated (Andre).
Walking Fern, https://www.flickr.com/photos/[email protected]/5865191366
The walking fern is named after the way that it spreads, in a walking-like manner. The parent’s leaves are long and cordate (triangular in shape, tapering to a thing point) and curl up and over to touch the ground. At the tip of the frond, where the leaf tissue touches the ground, a fertile pinnae contains spores and releases them to start new platelets in the nearby soil (Hilty). The leaves have entire margins and are undivided. They are usually found in low light habitats and in high pH rocks and soils (Key).
Bracken Fern, https://commons.wikimedia.org/wiki/File:E%C4%9Frelti_otu_-_Bracken_Fern_1.jpg
Found throughout the world in temperate and tropical climates, bracken fern is probably one of the most commonly distributed types of ferns. Its rootstocks have been measured to spread underground up to around 1300 feet in length and the fronds up to a hight of 16 feet, making it one of the largest plants in the world (Yatskievych). Because of this extensive root system, bracken ferns are almost impossible to remove, thus making them a tenacious colonizer, even noted as an invasive species in some places. It has been known to be used for thatching for houses, as the leaves are large and fringed. It has also been cooked as a vegetable in some types of Asian cuisine. If not cooked, bracken is may be harmful, as it contains a number of poisonous and carcinogenic compounds (Yatskievych). There are around ten subspecies of bracken, but the species commonly found in Missouri is the tailed bracken.
Mosquito Fern, https://commons.wikimedia.org/wiki/File:Azolla_filiculoides_MUN.jpg
The Azolla, one of the few aquatic fern genuses with fronds less than in inch in length, gets its common name “mosquito fern” from its tendency to cover the surfaces of bodies of fresh standing water, preventing mosquitoes (and other insects) from enter the water to lay eggs (Yatskievych, 2018). Particularly in bodies of water rich with nutrients, this fern is highly productive, forming a dense mat along the surface of the water. Despite being a native plant, it is often considered invasive because of the rapidity at which it grows and reproduces. It’s easily distinguishable by its green or red opposite leaves and its double lobed frond—one lobe above water and one below. The upper lobe often becomes home to colonies of cyanobacterium, a bacteria that captures atmospheric nitrogen and converts it into nitrate fertilizer. This symbiotic relationship piqued the interest of rice farmers of Southeast Asia years and years ago, and it has been widely used ever since to stimulate agricultural production in their rice paddies. Scientists also believe that the mosquito fern may have made a dramatic impact on the climate almost 50 million years ago. CO2 levels were rising and the sea levels were rising in response. However, it is theorized that mosquito ferns boomed in population, reproduced rapidly over the newly aquatic landscape, and absorbed almost half of the atmospheric CO2 (lowering it from about 3000 ppm to 1500 ppm (Jennifer Huizan, 2018)). This became nicknamed the “Azolla Event.” Some scientists are experimenting today with Azolla in the hopes of using it to aid in the reduction of greenhouse gases. Other scientists think that Azolla may be the “superfood of the future” because of its high nutritional value crossed with its minimal land and resource requirements.
Cinnamon Fern, https://commons.wikimedia.org/wiki/File:Cinnamon_fern.jpg
This fern gets its common name from its color. The fertile fronds, which look drastically different from the sterile fronds, originate as a bright green color then eventually turn brown or cinnamon colored. The sterile fronds also turn a yellowish color in autumn. Generally, this fern grows to be about 2-3 feet in height and width, but can reach up to 5 feet tall at optimal conditions of constant moisture. The cinnamon fern’s primary habitat is wet areas, along ponds and streams, as well as in shaded woodland areas (Missouri Botanical Garden).
Royal Fern, https://commons.wikimedia.org/wiki/File:OsmundaRegalis.jpg
This plant has distinct broad fronds with well-separated leaflets, making them look like a member of the pea family. Each plant has separate sterile and fertile fronds. The sterile fronds are much bigger and broader. The fertile fronds have several sterile leaflets, tipped by brown, tassel-like, fertile clusters that contain the plant’s spores. Because of these clusters’ strong resemblance of groups of flowers, royal ferns are often also nicknamed “flowering ferns.” Plants usually range from 2-3 feet in height and width and 6 feet under optimal conditions of constant moisture. It is native to Missouri, deciduous, and is mostly found in the southeastern Ozark region (Missouri Botanical Garden).
Ostrich Fern, https://www.flickr.com/photos/ideonexus/5924574123
Known for their big ostrich feather-like plumes, ostrich ferns can be found in temperate climates within Missouri, as well as all over the world. It has a unique structure made up of a vertical crown from which the sterile fronds extend and encircle the fertile spike frond. The fertile frond, with a dark, spiked, beadlike appearance, is located in the middle of the sterile fronds persists through winter and releases its spores in the spring. Ostrich ferns are commonly planted as ornamental plants in the garden for their thick plume-like fronds. They are known to spread widely from their rootstock (Key 112).
Maidenhair Fern, https://pixabay.com/en/maiden-hair-fern-leaf-flora-nature-3343037/
The fronds of this fern look quite different from most other ferns, as they have delicate, hanging fronds with two times pinnately compound, kidney shaped blades. Leaflets are alternate along the rachis as well as along the stems that branch off of the rachis. The sterile leaflets are variously lobed at the apex or along one side, entire or minutely toothed (Steyermark 146). The fertile leaflets’ margins are, on the other hand, mostly entire. The sporangia appear on the underside of the lobes of these leaflets. The veins of the leaflets, which branch dichotomously several times, can be seen easily with the naked eye. This is one of the most common and widespread ferns in Missouri (Steyermark 146).
Christmas Fern, photo by Mae Hubel
Christmas Fern, spores on underside, photo by Mae Hubel
This fern gets its name from its yearlong green color its fronds are often used for decorative purposes during during the Christmas season. Its leaflets have minute to coarse teeth (Key). The fertile pinnae and sterile pinnae are on the same frond. The fertile pinnae appear at the end of the blade, with narrower leaflets than the lower sterile pinnae and two rows of spores lining the underside of the pinnae (Key). Each pinna is auriculate at the base (Key). In other words, it contains a thumb-shaped lobe on one side at the base of each leaflet. Christmas ferns can be found in both moist and dry, preferably shaded areas. We found quite a few Christmas ferns in the wooded Lewis and Clark Trail on a November trip.
Common Horsetail, http://www.geograph.org.uk/photo/828907
Horsetails are particularly unique because they have hollow stems with several canals running up and down. The leaves of horsetails are joined at a whorled collar-shaped joint at regular intervals along the main stem. At the joints, there are also sheaths with black triangular teeth along the upper rim, encasing the next segment of the stem. The tips of the fertile fronds contain spore-bearing tips, characteristic by their inch-long, light brown cones with spore-bearing bumps. The fertile shoots are unbranched and shorter, and they usually develop during mid-spring and die out once they release their spores (Hilty). The sterile fronds develop around a similar time, but remain throughout the fall. They about twice as tall as the fertile fronds, and they have the branching, whorled structure at their joints (Hilty). Unlike most other ferns, horsetails thrive in dry and gravelly areas, rather than solely damp and temperate areas.
This family of lycophytes (or fern allies) have spores and spiky leaves, arranged spirally around one central strand. Most quillworts spend at least part of the year, if not all, growing submerged in water. The leaves of the plant grow from a cormlike base, or a vertical, underground stem. Terrestrial species of quillworts usually grow in seasonally wet habitats. Once the soil dries, the main part of the plant dies back to the cormlike base. At the inner surface of each leaf base, there’s a large saclike spore case that’s sunk into a pit. Some sterile quillwort hybrids exist, but some of them have been able to reproduce through a process called chromosome doubling (Yatskievych).
People used to try to use ferns for medicinal uses, but today these methods aren’t backed up by any scientific evidence. Nowadays, ferns are mainly used for decorations, weaving, dying, soap, glass, fertilizer, and in some places food. Fiddleheads, or young ferns whose leaves are still tightly curled up, are commonly used in cuisine. Royal ferns, among others, are commonly used for their fiddleheads. They are said to taste like asparagus. Osmunda fiber, or the brown colored fiber coming from the roots of cinnamon and royal ferns, is often used in the potting of orchids.
Azolla ferns have been used for centuries in agriculture, specifically in the rice paddies of eastern Asia. Because of the cyanobacterium living within the body fo these ferns, it participates in a symbiotic relationship that provides the bacteria with an environment to live and the aquatic fern with a supply of fixed nitrogen. This symbiotic relationship is particularly unique because it is the “only known symbiosis in which cyanobacterium passes directly to subsequent generations via the plant’s reproductive sporangia and spores” (The Azolla Foundation).
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Status and Revision History
Published on Sep 14, 2009
Published with Full Review on Aug 01, 2012
Published with Full Review on Oct 25, 2015