Azolla

Short description: Genus of aquatic plants

Azolla

Temporal range: Maastrichtian-Holocene

Azolla caroliniana
Scientific classification
Kingdom:  | Plantae
Clade:  | Tracheophytes
Division:  | Polypodiophyta
Class:  | Polypodiopsida
Order:  | Salviniales
Family:  | Salviniaceae
Genus:  | Azolla
Lam.[1]
Type species
Azolla filiculoides[1]

Lam.

Species

See text

Synonyms

* Carpanthus Rafinesque
* Rhizosperma Meyen

Azolla (mosquito fern, duckweed fern, fairy moss, water fern) is a genus of seven species of aquatic ferns in the family Salviniaceae. They are extremely reduced in form and specialized, looking nothing like other typical ferns but more resembling duckweed or some mosses. Azolla filiculoides is one of just two fern species for which a reference genome has been published.[2] It is believed that this genus grew so prolifically during the Eocene (and thus absorbed such a large amount of carbon) that it triggered a global cooling event that has lasted to the present.[3]

Azolla taken from the Philippines

Azolla may establish as an invasive plant in areas where it is not native [where?]. In such a situation it can alter aquatic ecosystems and biodiversity substantially.[4]

## Contents

* 1 Phylogeny
* 2 Ecology
* 2.1 Azolla filiculoides
* 3 Reproduction
* 4 Applications
* 4.1 Food and animal feed
* 4.2 Companion plant
* 4.3 Larvicide
* 4.4 Climate change
* 5 Invasive species
* 6 Importance in paleoclimatology
* 7 Bioremediation
* 8 References
* 9 External links

## Phylogeny

Phylogeny of Azolla[5][6]

Azolla |  |  |

A. nilotica Decne. ex Mett. (Nile Azolla)

|

|  |  |  |  |

A. filiculoides Lam. (Large mosquito fern)

|

A. rubra R.Br.

|  |  |

A. caroliniana Willdenow 1810 (Eastern/Carolinian mosquito fern)

|

|  |  |

Azolla cristata Kaulf. (Mexican mosquito fern)

|

A. pinnata R.Br. (Ferny/Pacific Azolla; Feathered mosquitofern)

Other species include:[7][8][9][10]

Drawing of Azolla filiculoides, about 5 mm. Upper green leaves perform photosynthesis, lower lack chlorophyll.

At least six extinct species are known from the fossil record:

* Azolla intertrappea Sahni & H.S. Rao, 1934 (Eocene, India )[11]
* Azolla berryi Brown, 1934 (Eocene, Green River Formation, Wyoming)[11]
* Azolla prisca Chandler & Reid, 1926 (Oligocene, London Clay, Isle of Wight)[11]
* Azolla tertiaria Berry, 1927 (Pliocene, Esmeralda Formation, Nevada)[11]
* Azolla primaeva (Penhallow) Arnold, 1955 (Eocene, Allenby Formation, British Columbia)[11]
* Azolla boliviensis Vajda & McLoughlin, 2005 (Maastrichtian \- Paleocene, Eslaboacuten Formation and Flora Formation Bolivia)[12]

## Ecology

Azolla filiculoides root cross section Azolla covering the Canning River, Western Australia Azolla on the Canning River, Western Australia

Azolla is a highly productive plant. It can double its biomass in as little as 1.9 days,[13] depending on growing conditions, and yield can reach 8–10 tonnes fresh matter/ha in Asian rice fields. 37.8 t fresh weight/ha (2.78 t DM/ha dry weight) has been reported for Azolla pinnata in India (Hasan et al., 2009).[14]

Azolla floats on the surface of water by means of numerous small, closely overlapping scale-like leaves, with their roots hanging in the water. They form a symbiotic relationship with the cyanobacterium Anabaena azollae, an extracellular endosymbiont (living outside the host's cells) which fixes atmospheric nitrogen.[15] The typical limiting factor on its growth is phosphorus; thus, an abundance of phosphorus - due for example to eutrophication or chemical runoff - often leads to Azolla blooms. Unlike all other known plants, its symbiotic microorganism transfers directly from one generation to the next. A. azollae is completely dependent on its host, as several of its genes have either been lost or transferred to the nucleus in Azolla's cells.[16]

SEM image of Azolla surface

The nitrogen-fixing capability of Azolla has led to widespread use as a biofertiliser, especially in parts of southeast Asia. The plant has been used to bolster agricultural productivity in China for over a thousand years. When rice paddies are flooded in the spring, they can be planted with Azolla, which then quickly multiplies to cover the water, suppressing weeds. The rotting plant material resulting from the die off of this Azolla releases nitrogen into the water for the rice plants, providing up to nine tonnes of protein per hectare per year.[17]

Azolla are weeds in many parts of the world, entirely covering some bodies of water. The myth that no mosquito can penetrate the coating of fern to lay its eggs in the water gives the plant its common name "mosquito fern",[18] and may deter the survival of some of the larvae.

Most species can produce large amounts of deoxyanthocyanins in response to various stresses,[19] including bright sunlight and extreme temperatures,[20][21] causing the water surface to appear to be covered with an intensely red carpet. Herbivore feeding induces accumulation of deoxyanthocyanins and leads to a reduction in the proportion of polyunsaturated fatty acids in the fronds, thus lowering their palatability and nutritive value.[22]

Azolla cannot survive winters with prolonged freezing, so is often grown as an ornamental plant at high latitudes where it cannot establish itself firmly enough to become a weed. It is also not tolerant of salinity; normal plants cannot survive in greater than 1–1.6‰, and even conditioned organisms die if grown in water with a salinity above 5.5‰.[23][3]

### Azolla filiculoides

Azolla filiculoides (red azolla) is the only member of this genus and of the family Azollaceae in Tasmania. It is a common native aquatic plant in Tasmania. It is common behind farm dams and other still waterbodies. The plants are small (usually only a few cm across) and float, but they are fast growing, and can be abundant and form large mats. The plants are typically red, and have small, water repellent leaves.

## Reproduction

Scanning electron micrograph of a megaspore of the genus Azolla with adhering massulae from postal sediments of Laguna El Junco, Galápagos Island of San Cristóbal[24] Transmission electron micrograph of a megaspore of the genus Azolla from postglacial sediments of Laguna El Junco, Galápagos Island of San Cristobal[24]

Azolla reproduces sexually, and asexually (by splitting).

Like all ferns, sexual reproduction leads to spore formation, but unlike other members of this group Azolla is heterosporous, producing spores of two kinds. During the summer months, numerous spherical structures called sporocarps form on the undersides of the branches. The male sporocarp is greenish or reddish and looks like the egg mass of an insect or spider. It is two millimeters in diameter, and bears numerous male sporangia. Male spores (microspores) are extremely small and are produced inside each microsporangium. Microspores tend to adhere in clumps called massulae.[11]

Female sporocarps are much smaller, containing one sporangium and one functional spore. Since an individual female spore is considerably larger than a male spore, it is termed a megaspore.

Azolla has microscopic male and female gametophytes that develop inside the male and female spores. The female gametophyte protrudes from the megaspore and bears a small number of archegonia, each containing a single egg. The microspore forms a male gametophyte with a single antheridium which produces eight swimming sperm.[25] The barbed glochidia on the male spore clusters cause them to cling to the female megaspores, thus facilitating fertilization.

## Applications

### Food and animal feed

In addition to its traditional cultivation as a bio-fertilizer for wetland paddies, Azolla is finding increasing use for sustainable production of livestock feed.[26] Azolla is rich in protein, essential amino acids, vitamins, and minerals. Studies describe feeding Azolla to dairy cattle, pigs, ducks, and chickens, with reported increases in milk production, weight of broiler chickens and egg production of layers, as compared to conventional feed. One FAO study describes how Azolla integrates into a tropical biomass agricultural system, reducing the need for food supplements.[27] Concerns about biomagnification exist because the plant may contain the neurotoxin BMAA that remains present in the bodies of animals consuming it and BMAA has been documented as passing along the food chain.[28] Azolla may contain this substance that is a possible cause of neurodegenerative diseases.[29][30][31] Azolla has been suggested as a foodstuff for human consumption, however, no long-term studies of the safety of eating Azolla have been made on humans.[32] Previous studies attributed neurotoxin production to Anabaena flos-aquae species, which is also a type of nitrogen-fixing cyanobacteria.[33] Further research may be needed to ascertain if A. azollae produces neurotoxins.

### Companion plant

Azolla has been used for at least one thousand years in rice paddies as a companion plant, to fix nitrogen and to block out light to prevent competition from other plants. Rice is planted when tall enough to poke through the Azolla layer. Mats of mature Azolla can also be used as a weed-suppressing mulch.

Rice farmers used Azolla as a rice biofertilizer 1500 years ago. The earliest known written record of this practice is in a book written by Jia Ssu Hsieh (Jia Si Xue) in 540 A.D on The Art of Feeding the People (Chih Min Tao Shu). By the end of the Ming dynasty in the early 17th century, Azolla’s use as a green compost was documented in local records.[34]

### Larvicide

The myth that no mosquito can penetrate the coating of fern to lay its eggs in the water gives the plant its common name "mosquito fern".[18] Azolla have been used to control mosquito larvae in rice fields. The plant grows in a thick mat on the surface of the water, making it more difficult for the larvae to reach the surface to breathe, effectively choking the larvae.[35]

### Climate change

Azolla has been proposed as a carbon sequestration modality. The proposal draws upon the hypothesized Azolla event that asserts that Azolla once covered the Arctic and then sank, permanently sequestering teratons of carbon that would otherwise have contributed to the planet's greenhouse effect and ending a warming event that reached 12–15 °C (22–27 °F) degrees warmer than twenty-first century averages.[36]

They contribute significantly to decreasing the atmospheric CO2 levels.[3]

## Invasive species

This fern has been introduced to other parts of the world, including the United Kingdom , where it has become a pest in some areas. A nominally tropical plant, it has adapted to the colder climate. It can form mats up to 30 centimetres (12 in) thick and cover 100% of a water surface, preventing local insects and amphibians from reaching the surface.[37]

## Importance in paleoclimatology

Main article: Earth:Azolla event

A study of Arctic paleoclimatology reported that Azolla may have had a significant role in reversing an increase in greenhouse effect that occurred 55 million years ago that had caused the region around the north pole to turn into a hot, tropical environment. This research was conducted by the Institute of Environmental Biology at Utrecht University. It indicates that massive patches of Azolla growing on the (then) freshwater surface of the Arctic Ocean consumed enough carbon dioxide from the atmosphere for the global greenhouse effect to decline, eventually causing the formation of ice sheets in Antarctica and the current "icehouse period". This theory has been termed the Azolla event.[38]

## Bioremediation

Azolla can remove chromium, nickel, copper, zinc, and lead from effluent. It can also remove lead from solutions containing 1–1000 ppm.[39]

## References

1. ↑ 1.0 1.1 In: Encyclopédie Méthodique, Botanique 1(1): 343. 1783. "Name - Azolla Lam.". Tropicos. Saint Louis, Missouri: Missouri Botanical Garden. http://www.tropicos.org/Name/40023609. "Annotation: a sp. nov. reference for Azolla filiculoides
Type Specimens HT: Azolla filiculoides"
2. ↑ Li, Fay-Wei; Brouwer, Paul; Carretero-Paulet, Lorenzo; Cheng, Shifeng; de Vries, Jan; Delaux, Pierre-Marc; Eily, Ariana; Koppers, Nils et al. (2018-07-02). "Fern genomes elucidate land plant evolution and cyanobacterial symbioses" (in En). Nature Plants 4 (7): 460–472. doi:10.1038/s41477-018-0188-8. ISSN 2055-0278. PMID 29967517.
3. ↑ 3.0 3.1 3.2 Speelman, E. N.; Van Kempen, M. M. L.; Barke, J.; Brinkhuis, H.; Reichart, G. J.; Smolders, A. J. P.; Roelofs, J. G. M.; Sangiorgi, F. et al. (March 2009). "The Eocene Arctic Azolla bloom: environmental conditions, productivity and carbon drawdown" (in en). Geobiology 7 (2): 155–170. doi:10.1111/j.1472-4669.2009.00195.x. PMID 19323694. Bibcode: 2009Gbio....7..155S. https://onlinelibrary.wiley.com/doi/10.1111/j.1472-4669.2009.00195.x.
4. ↑ Weber, Ewald (2017). Invasive Plant Species of the World: A Reference Guide to Environmental Weeds. p. 65. ISBN 9781780643861. https://books.google.com/books?id=Ns_UDgAAQBAJ.
5. ↑ Nitta, Joel H.Expression error: Unrecognized word "et". (2022). "An Open and Continuously Updated Fern Tree of Life". Frontiers in Plant Science 13: 909768. doi:10.3389/fpls.2022.909768. PMID 36092417.
6. ↑ "Tree viewer: interactive visualization of FTOL". 2023. https://fernphy.github.io/viewer.html.
7. ↑ Evrard, C.; Van Hove, C. (2004). "Taxonomy of the American Azolla species (Azollaceae): A critical review". Systematics and Geography of Plants 74: 301–318.
8. ↑ "Name - Azolla Lam. subordinate taxa". Tropicos. Saint Louis, Missouri: Missouri Botanical Garden. http://www.tropicos.org/NameSubordinateTaxa.aspx?nameid=40023609.
9. ↑ "Query Results for Genus Azolla". IPNI. http://www.ipni.org:80/ipni/advPlantNameSearch.do?find_genus=Azolla&find_rankToReturn=spec&output_format=normal&query_type=by_query&back_page=plantsearch.
10. ↑ Hussner, A. (2006). "NOBANIS -- Invasive Alien Species Fact Sheet -- Azolla filiculoides". Online Database of the North European and Baltic Network on Invasive Alien Species. Heinrich Heine Universität, Düsseldorf. http://www.nobanis.org/files/factsheets/Azolla_filiculoides.pdf.
11. ↑ 11.0 11.1 11.2 11.3 11.4 11.5 Arnold, C.A. (1955). "A Tertiary Azolla from British Columbia". Contributions from the Museum of. Paleontology, University of Michigan 12 (4): 37–45. http://deepblue.lib.umich.edu/bitstream/2027.42/48289/2/ID129.pdf.
12. ↑ Vajda, V; McLoughlin, S. (2005). "A new Maastrichtian-Paleocene Azolla species from Bolivia, with a comparison of the global record of coeval Azolla microfossils". Alcheringa: An Australasian Journal of Palaeontology 29 (2): 305–329. doi:10.1080/03115510508619308.
13. ↑ Iwao Watanabe, Nilda S.Berja (1983). "The growth of four species of Azolla as affected by temperature". Aquatic Botany 15 (2): 175–185. doi:10.1016/0304-3770(83)90027-X.
14. ↑ "Hasan, M. R.; Chakrabarti, R., 2009. Use of algae and aquatic macrophytes as feed in small-scale aquaculture: A review. FAO Fisheries and Aquaculture technical paper, 531. FAO, Rome, Italy". https://www.fao.org/3/i1141e/i1141e00.htm.
15. ↑ Ran, L.; Larsson, J.; Vigil-Stenman, T.; Nylander, J. A.; Ininbergs, K.; Zheng, W. W.; Lapidus, A.; Lowry, S. et al. (2010). "Genome Erosion in a Nitrogen-Fixing Vertically Transmitted Endosymbiotic Multicellular Cyanobacterium". PLOS ONE 5 (7): e11486. doi:10.1371/journal.pone.0011486. PMID 20628610. Bibcode: 2010PLoSO...511486R.
16. ↑ The Arctic Azolla event - The Geological Society
17. ↑ "FAO figures". http://www.fao.org/ag/AGA/AGAP/FRG/afris/DATA/558.htm.
18. ↑ 18.0 18.1 "Mosquito Fern". America's Wetland Resource Center. Loyola University, New Orleans. http://www.americaswetlandresources.com/wildlife_ecology/plants_animals_ecology/plants/mosquitofern.html.
19. ↑ Wagner, G.M. (1997). "Azolla: a review of its biology and utilization". Bot. Rev. 63: 1–26. doi:10.1007/BF02857915.
20. ↑ Moore, A. W. (1969). "Azolla: Biology and agronomic significance". Bot. Rev. 35: 17–35. doi:10.1007/BF02859886.
21. ↑ Zimmerman, William J. (1985). "Biomass and Pigment Production in Three Isolates of Azolla II. Response to Light and Temperature Stress". Ann. Bot. 56 (5): 701–709. doi:10.1093/oxfordjournals.aob.a087059.
22. ↑ Cohen, M.F.; Meziane, T.; Tsuchiya, M.; Yamasaki, H. (2002). "Feeding deterrence of Azolla in relation to deoxyanthocyanin and fatty acid composition". Aquatic Botany 74 (2): 181–187. doi:10.1016/S0304-3770(02)00077-3. http://www.bashanfoundation.org/michael/michaelfeeding.pdf. Retrieved 2010-01-22.
23. ↑ Brinkhuis, H. et al. (2006). "Episodic fresh surface waters in the Eocene Arctic Ocean". Nature 441 (7093): 606–9. doi:10.1038/nature04692. PMID 16752440. Bibcode: 2006Natur.441..606B. http://www.nature.com/search/executeSearch?sp-q-9=NATURE&sp-q=Episodic+fresh+surface+waters+in+the+Eocene+Arctic+Ocean&sp-c=10&sp-x-9=cat&sp-s=date&submit=go&sp-a=sp1001702d&sp-sfvl-field=subject|ujournal&sp-x-1=ujournal&sp-p-1=phrase&sp-p=all. Retrieved 2007-10-17.
24. ↑ 24.0 24.1 Kempf, E.K. (1976). "Low Magnifications - A Marginal Area of Electron Microscopy". ZEISS Information 21 (83): 57–60.
25. ↑ Scagel, Robert F.; Bandoni, Robert J.; Rouse, Glenn E.; Schofield, W.B.; Stein, Janet R.; Taylor, T.M. (1965). An Evolutionary Survey of the Plant Kingdom. Belmont, California: Wadsworth Publishing. 658 pp.
26. ↑ Pillai, P. Kamalasanana; Premalatha, S.; Rajamony, S.. "Azolla – a sustainable feed substitute for livestock". Farming Matters magazine. Azolla livestock feed. http://www.agriculturesnetwork.org/magazines/global/small-animals-in-focus/azolla-livestock-feed. Retrieved 2008-01-14.
27. ↑ Preston, T.R.; Murgueitio, E. (1992–1993). "Sustainable intensive livestock systems for the humid tropics". World Animal Review. Sustainable animal production (UN FAO) 71. ISSN 1014-6954. http://www.fao.org/docrep/u7600t/u7600T04.htm. Retrieved 2011-09-28.
28. ↑ Banack, S.A.; Cox, P.A. (2003). "Biomagnification of cycad neurotoxins in flying foxes: Implications for ALS-PDC in Guam". Neurology 61 (3): 387–389. doi:10.1212/01.wnl.0000078320.18564.9f. PMID 12913204.
29. ↑ Sjodin, Erik (December 2014). "Azolla, BMAA, and neurodegenerative diseases". https://www.academia.edu/10074317.
30. ↑ "Are toxins in seafood causing ALS, Alzheimer's, and Parkinson's?". Discover Magazine. May 2011. http://discovermagazine.com/2011/may/22-seafood-toxins-causing-als-alzheimers-parkinsons. Retrieved 2019-09-13.
31. ↑ Williams, Amy Bennett (7 August 2019). "Documentary about algae and public health debuts to sold-out crowd". Fort Myers News-Press. https://www.news-press.com/story/tech/science/environment/2019/08/07/documentary-algae-and-public-health-debuts-sold-out-crowd/1926083001/.
32. ↑ Sjodin, Erik (2012). The Azolla Cooking and Cultivation Project. Erik Sjödin. ISBN 978-9198068603.
33. ↑ Agnihotri, Vijai K. (2014). "Anabaena flos-aquae". Critical Reviews in Environmental Science and Technology 44 (18): 1995–2037. doi:10.1080/10643389.2013.803797.
34. ↑ "The East discovers Azolla". http://theazollafoundation.org/azolla/azollas-use-in-the-east/.
35. ↑ Myer, Landon; Okech, Bernard A.; Mwobobia, Isaac K.; Kamau, Anthony; Muiruri, Samuel; Mutiso, Noah; Nyambura, Joyce; Mwatele, Cassian et al. (2008). Myer, Landon. ed. "Use of Integrated Malaria Management Reduces Malaria in Kenya". PLOS ONE 3 (12): e4050. doi:10.1371/journal.pone.0004050. PMID 19115000. Bibcode: 2008PLoSO...3.4050O.
36. ↑ Wang, Brian. "Fix Hothouse Earth Just Like Last Time | NextBigFuture.com" (in en-US). https://www.nextbigfuture.com/2021/08/fix-hothouse-earth-just-like-last-time.html.
37. ↑ Invasive non-native species (UK) – Water fern – Inside Ecology
38. ↑ "Can A Tiny Fern Help Fight Climate Change and Cut Fertilizer Use?" (in en-US). 2018-07-11. https://e360.yale.edu/digest/can-a-tiny-fern-help-fight-climate-change-and-cut-fertilizer-use-azolla.
39. ↑ Robert L. Irvine; Subhas K. Sikdar (1998-01-08). Bioremediation Technologies: Principles and Practice. CRC Press. p. 102. ISBN 9781566765619. https://books.google.com/books?id=oLNtgk_VKXsC&q=Bioremediation+of+gypsum&pg=PA81.

## External links

* The Azolla Foundation: Azolla Non-Profit Information & Guidance Website
* Azolla Philippines: A website dedicated to the distribution of Azolla for propagation as alternative livestock feed.
* Marriage Between A Fern & Cyanobacterium
* NSW Flora online: Azolla

* v
* t
* e

Classification of Archaeplastida / Plantae sensu lato

Domain
Archaea
Bacteria
Eukaryota
(Supergroup
Plant
Hacrobia
Heterokont
Alveolata
Rhizaria
Excavata
Amoebozoa
Opisthokonta

Animal
Fungi)

Rhodophyta
(red algae)|

* Cyanidiophyceae
* Porphyridiophyceae
* Compsopogonophyceae
* Stylonematophyceae
* Rhodellophyceae
* Bangiophyceae
* Florideophyceae

Glaucocystophyta
(glaucophytes)|

* Glaucocystophyceae
* Glaucocystis
* Cyanophora
* Gloeochaete

Viridiplantae
(green algae,
& land plants)|

| M+C+S|

* Mesostigmatophyceae
* Chlorokybophyceae
* Spirotaenia

|

C+S|

| Chlorophyta
(prasinophytes)|

* Mamiellophyceae
* Nephrophyceae
* Palmophyllales
* Prasinophyceae
* Pseudoscourfieldiales
* Pyramimonadophyceae
* Scourfieldiales
* Pedinophyceae
* Chlorodendrophyceae
* UTC clade
* Ulvophyceae
* Trebouxiophyceae
* Chlorophyceae

|

Streptophyta
(charophytes,
& land plants)|

* Klebsormidiophyceae

Phragmo-
plastophyta|

* Charophyceae
* Coleochaetophyceae
* Zygnematophyceae
* Mesotaeniaceae

Embryophyta
(land plants)|

| Bryophytes
(non-vascular)|

* Marchantiophyta
* Anthocerotophyta
* Bryophyta "Moss"
* †Horneophytopsida

|

Tracheophyta
(vascular)|

| Lycopodiophyta
(microphylls)|

* †Zosterophyllopsida
* †Sawdoniales
* Isoetopsida
* Lycopodiopsida

|

Euphyllophyta
(megaphylls)|

| Polypodiopsida
(ferns)|

* †Cladoxylopsida
* †Stauropteridales
* †Zygopteridales
* Equisetidae
* Ophioglossidae
* Marattiidae
* Polypodiidae

|

Spermatophyta
(seed plants)|

* †Seed ferns
* Gymnosperms
* Gnetopsida
* Pinopsida
* Cycadopsida
* Ginkgoopsida
* Angiosperms or flowering plants
* Amborellales
* Nymphaeales
* Austrobaileyales
* Magnoliids
* Monocots
* Eudicots

Other|

* †Trimerophytopsida
* †Progymnosperm

Other|

* †Rhyniopsida

† = extinct. See also the list of plant orders.

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