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Azolla filiculoides
Azolla filiculoides
Azolla filiculoides
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Azolla filiculoides
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Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Division: Polypodiophyta
Class: Polypodiopsida
Order: Salviniales
Family: Salviniaceae
Genus: Azolla
Species:
A. filiculoides
Binomial name
Azolla filiculoides
Synonyms[2][3]
  • Azolla arbuscula Desv.
  • Azolla caroliniana Willd.
  • Azolla japonica Franch. & Sav.
  • Azolla magellanica Willd.
  • Azolla microphylla Kaulf.
  • Azolla pinnata var. japonica (Franch. & Sav.) Franch. & Sav.
  • Azolla squamosa Molina

Azolla filiculoides (water fern) is a species of aquatic fern. It is native to warm temperate and tropical regions of the Americas, and has been introduced to Europe, North and sub-Saharan Africa, China, Japan, New Zealand, the Caribbean, and Hawaii.[4]

It is a floating aquatic fern with very fast growth, capable of spreading over the surfaces of lakes to give complete coverage of the water in only a few months. Each individual plant is 1–2 cm across, green tinged pink, orange, or red at the edges, branching freely, and breaking into smaller sections as it grows. It is not tolerant of cold temperatures; in temperate regions it largely dies back in winter, surviving by means of submerged buds. It harbors the diazotrophic organism Anabaena azollae in specialized leaf pockets. This ancient symbiosis allows A. azollae to fix nitrogen from the air and contribute to the fern's metabolism.[5][6]

Fossil records from as recent as the last interglacials are known from several locations in Europe (Hyde et al. 1978). 50 million years ago, a species similar to A. filiculoides may have played a pivotal role in cooling the planet in what is known as the Azolla event.[7]

A. filiculoides was one of the first two fern species with a reference genome published.[8][7]

Identification

[edit]

The only sure method of distinguishing this species from A. cristata (long incorrectly known as A. caroliniana) is to examine the trichomes on the upper surfaces of the leaves. Trichomes are small protuberances that create water resistance. They are unicellular in A. filiculoides but septate (two-celled) in A. cristata.[9]

Cultivation

[edit]

The species has been introduced to many regions of the Old World, grown for its nitrogen-fixing ability that may be used to enhance the growth rate of crops grown in water, such as rice, or by removal from lakes for use as green manure.[10] A. filiculoides is frequently cultivated in aquariums and ponds, where it can become easily dominant over other species.

Invasive species

[edit]

A. filiculoides was first recorded in Europe in 1870s–1880s, when the species may have been accidentally transported in ballast water, with fry, or directly as an ornamental or aquarium plant. It was introduced into Asia from East Germany in 1977 as an alternative to the cold susceptible native strain of A. pinnata, used as a green manure in the rice industry. A. filiculoides has also been spread around the world as a research model plant for the study of Azolla–Anabaena symbiosis. In the areas of introduction, A. filiculoides is capable of rapid growth, especially in eutrophic ecosystems, and outcompetes native aquatic plants. The dense mat of A. filiculoides causes lack of light penetration and an anaerobic environment due to detritus decomposition, causing a drastic reduction of water quality, aquatic biodiversity, and ecosystem function.[11][12]

See also

[edit]
[edit]
  • Close-up of a leaf
    Close-up of a leaf
  • A. filiculoides (pink-tinged) with Lemna minor
    A. filiculoides (pink-tinged) with Lemna minor
  • Single A. filiculoides plant showing the roots
    Single A. filiculoides plant showing the roots

References

[edit]

Further reading

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Azolla filiculoides

View on Grokipedia
from Grokipedia
Azolla filiculoides, commonly known as the Pacific mosquitofern or American waterfern, is a small, free-floating aquatic fern species in the family Azollaceae, characterized by its rapid growth and ability to form dense mats on the surface of still or slow-moving waters. This species features branched, fan-shaped fronds typically measuring 1–5 cm in length, with overlapping scalelike leaves that can appear , red, or pink depending on environmental conditions such as sunlight and temperature; it possesses pendent roots and reproduces primarily vegetatively through fragmentation, though it also produces spores. Native to warm temperate and tropical regions of the , A. filiculoides has been introduced to many areas in the , where it thrives in freshwater habitats like ponds, ditches, and paddies, playing a key ecological role in nutrient cycling and management. A defining feature of Azolla filiculoides is its unique with the obligate nitrogen-fixing cyanobacterium azollae (formerly azollae), which resides in specialized leaf cavities and enables the to fix atmospheric at rates of 2–4 kg N/ha/day under optimal conditions. This vertically transmitted partnership, which shows evidence of cospeciation between the fern and cyanobiont over millions of years, allows A. filiculoides to thrive in nutrient-poor waters without external nitrogen inputs, contributing up to 30–60 kg N/ha per growing season when incorporated into agricultural systems. Evolutionarily, the species has a compact of approximately 0.75 Gb—unusually small for ferns—and experienced a whole-genome duplication after diverging from its sister genus around 100 million years ago. Ecologically, Azolla filiculoides forms expansive surface mats that suppress submersed vegetation, reduce water evaporation by up to 60%, and inhibit larvae development, earning it the "mosquitofern" moniker; however, in some regions, its rapid spread can make it invasive, outcompeting native plants. Historically, dense blooms of ancient species, including ancestors of A. filiculoides, are linked to the Eocene "" approximately 50 million years ago, where massive —estimated at 21,266 kg C (carbon)/ha/year, equivalent to approximately 78,000 kg CO₂/ha/year, in modern analogs—contributed to by burying in the . In agriculture, Azolla filiculoides has been utilized for over 1,000 years in as a for cultivation, where it boosts yields by enhancing , suppressing weeds by up to 50%, and reducing from paddies by 30–60%. Beyond farming, it serves as a high-protein (25–35% crude protein) feed, improving milk yields by 7–20%, and shows promise in by removing 70–94% of like lead and from polluted waters, as well as in and production. These attributes position A. filiculoides as a valuable tool for sustainable practices amid challenges.

Taxonomy

Classification

Azolla filiculoides is classified within the kingdom Plantae, division Polypodiophyta (formerly Pteridophyta in older systems), class Polypodiopsida, order Salviniales, family Azollaceae, Azolla, and species filiculoides. Phylogenetically, A. filiculoides belongs to the heterosporous ferns, positioned within the Azolla, which comprises seven extant species divided into two sections: the Americas-based section Azolla (including A. filiculoides and its species A. cristata) and the section Rhizosperma (including A. pinnata). The Azolla (family Azollaceae) forms a monophyletic to the Salvinia (family Salviniaceae), together comprising the order Salviniales, which is part of the marsileaceous-fern lineage within leptosporangiate ferns. The species was originally described by Jean-Baptiste Lamarck in 1783 as Azolla filiculoides in the Encyclopédie Méthodique. Taxonomy of the genus has been revised multiple times due to morphological similarities among species, with a key 2004 review by Evrard and Van Hove clarifying distinctions among American Azolla taxa, including the separation of A. filiculoides from synonyms like A. caroliniana. No major taxonomic updates have occurred since 2020, though the genus remains challenging to delineate based on morphology alone. In 2018, A. filiculoides became the first fern species with a reference genome sequenced, revealing a genome size of approximately 0.75 Gb and a chromosome number of 2n=44 (base number n=22). This genomic resource has supported phylogenetic analyses confirming its placement within the Salviniales order.

Etymology and Synonyms

The genus name derives from the Greek words azō (to dry) and olluō (to kill), alluding to the plant's inability to survive when removed from water. The specific epithet filiculoides comes from the Latin filix () and the Greek -oides (resembling), reflecting the species' small, fern-like fronds. This binomial was first published by in 1783, based on specimens from warm temperate and tropical regions of the , which serve as the type locality. Azolla filiculoides is the accepted name according to major taxonomic databases as of 2025, including the (ITIS) and the (NCBI) taxonomy. Historical synonyms include Azolla caroliniana Willd. (1802), now considered a direct following revision of type material, and Azolla rubra R. Br. (1810), often treated as a variety (A. filiculoides var. rubra (R. Br.) Strasb.). Other synonyms encompass A. arbuscula Desv., A. magellanica Willd., and A. squamosa Molina, reflecting early confusion in delimiting Azolla species. In modern , A. filiculoides is distinguished from the morphologically similar A. cristata Kaulf. primarily by its unicellular trichomes versus the bicellular ones in A. cristata.

Description

Morphology

Azolla filiculoides is a small, free-floating aquatic fern that forms dense, rapidly expanding mats on the surface of still or slow-moving freshwater bodies. Individual plants typically measure 1–2.5 cm in length, with freely branching fronds that are triangular to ovate in outline and exhibit a green coloration accented by reddish to purplish margins. The leaves are sessile, alternate, and bipartite, comprising a dorsal lobe that is photosynthetic, overlapping, and scale-like, and a ventral lobe that is root-like, thin, translucent, and submerged. The dorsal lobe bears unicellular trichomes, a trait that aids in distinguishing A. filiculoides from congeners like Azolla cristata, which possess multicellular trichomes. Sporocarps develop on the ventral side of the fronds, with microsporocarps appearing globose and approximately 1.5 mm in diameter, while megasporocarps house megaspores equipped with distinctive glochidia—spiny, hook-like appendages often featuring 0–2 septa that are characteristic of the species. Color variations reflect environmental responses: fronds remain green under low-light conditions but shift to red or pink hues in high light or under stress, owing to anthocyanin accumulation. In temperate climates, the plant frequently dies back during winter, adopting a reddish tint before dormancy.

Anatomy

The fronds of Azolla filiculoides consist of bilobed leaves arranged in two alternating rows along branched stems, with the dorsal lobe positioned above the surface and the ventral lobe submerged. The dorsal lobe is thick and chlorophyllous, featuring extensive air-filled lacunae that form a spongy tissue essential for and structural support. These lacunae, interconnected by diaphragms, allow for gas storage and diffusion while minimizing waterlogging. In contrast, the ventral lobe is thin, translucent, and achlorophyllous, containing the primary —a central with and —that extends into pendent adventitious . The ventral lobe produces functional root hairs that enhance and uptake from the surrounding medium. The surface of the dorsal lobe is adorned with unicellular, non-septate trichomes, which are elongated hairs emerging from epidermal cells. These trichomes play a critical role in by facilitating the diffusion of oxygen and across the leaf surface and contribute to water repellency, creating a hydrophobic barrier that maintains the plant's dry upper surface despite its aquatic . Their unicellular base and lack of septa distinguish A. filiculoides from related like A. cristata, where trichomes are two-celled. Sporocarps, the reproductive structures, develop singly or in pairs on the ventral lobe and are enclosed by indusia. Microsporocarps are stalked and contain numerous microsporangia, each containing multiple massulae (typically 32–64), with each massula consisting of 16–32 cohering microspores; these massulae bear numerous glochidia—barbed, anchor-like appendages—that aid in attachment and dispersal by entangling with floating debris or the female structures. Megasporocarps, in contrast, are sessile and enclose a single megasporangium with one large megaspore, also equipped with a single prominent glochidium at its apex. The megaspore wall is ornamented with a perine layer featuring float-like structures and a thick exine, adaptations that promote flotation and long-distance dispersal across water bodies. Under optimal environmental conditions of 25–30°C and full , A. filiculoides demonstrates exceptional growth vigor, achieving a doubling time of 1.9–7.3 days, which underscores its potential for rapid colonization of aquatic surfaces.

Reproduction and Life Cycle

Sexual Reproduction

_Azolla filiculoides exhibits , a reproductive strategy characteristic of advanced , wherein the diploid produces two distinct types of spores in separate sporocarps on the same . Microsporocarps develop on the adaxial side of the first ventral lobe of a and contain multiple microsporangia, each producing 32-64 microspores that aggregate into massulae equipped with glochidia for attachment. Megasporocarps form similarly but contain a single functional megasporangium that yields one large functional megaspore accompanied by several aborted megaspores, which contribute to the flotation apparatus and a multi-layered wall for protection. Gametophyte formation occurs endosporically within the detached sporocarps, which sink to the as resting structures. Microspores germinate to form multi-celled male that differentiate into antheridia, producing motile, multiflagellated capable of swimming in . Megaspores develop into female retained within the spore wall, where the prothallus produces multiple archegonia containing eggs; the female remains enclosed, providing a protected environment for subsequent development. Mature megaspores are provisioned with protein bodies, globules, and to support this internal growth. Fertilization takes place underwater, as motile from the male are released and swim to reach the egg in an of the female , often facilitated by the glochidia anchoring massulae near the megasporocarp. This process is rare in natural populations owing to stringent environmental triggers, such as far-red enrichment under dense canopies and availability, which limit sporocarp induction and result in predominantly . Successful crosses under controlled conditions can yield over 1,000 viable sporelings, confirming the potential for despite its infrequency. Sporocarps typically mature on the within one to two weeks under inductive conditions, after which they detach and enable gametophyte maturation over days to weeks depending on and light. Following fertilization, the divides to form a multicellular within the megaspore, which differentiates into a young featuring a foot, , and first ; this fills the prothallus before emerging through a perineal pore, maintaining symbiotic continuity.

Vegetative Reproduction

Azolla filiculoides primarily propagates vegetatively through clonal growth originating from shoot apical , which produce lateral branches that develop into independent fronds interconnected by a branched stem, ultimately forming expansive floating mats. This branching pattern, characterized by alternate development, allows for continuous expansion without the need for sexual structures, with new fronds emerging sequentially from the meristem. Fragmentation occurs via natural at branch nodes, where enzymatic degradation of the detaches segments, each capable of rapid regeneration into viable plants due to retained photosynthetic and symbiotic capabilities. The rate of this clonal expansion is exceptionally high, enabling to double every 1.9 to 5 days under nutrient-rich conditions such as levels around 1.5 mg/L and adequate (12-hour photoperiod), far outpacing many terrestrial . Factors like availability and (optimal at 20–30°C) drive this proliferation, with mother exhibiting high (up to 215 days) and low mortality (approximately 1.6%). Physical dispersal of fragments by , currents, or animal activity further accelerates , as even small pieces can establish new populations in suitable aquatic environments. In temperate climates, includes the formation of dormant winter buds or resting tubers that sink to the , allowing survival through cold periods when surface fronds die back. These structures, tolerant of sub-zero temperatures above -, germinate in spring upon warming, enabling rapid resurgence of mats from overwintering propagules. This mode of apomixis-like cloning, dominant over infrequent , results in low within populations, as successive generations are genetically identical to the parent, potentially limiting adaptability but enhancing uniform invasiveness.

Habitat and Distribution

Native Range

_Azolla filiculoides is native to warm temperate and tropical regions across the , with its original distribution spanning western —from and southward through the Rocky Mountain states, , and —extending via and into , including countries such as , , , , and . This species occupies freshwater ecosystems prior to any human-mediated dispersal, distinguishing it from related taxa like Azolla caroliniana, which is confined to eastern . In its native habitats, A. filiculoides prefers still or slow-moving water bodies, including , lakes, ditches, sluggish rivers, and occasionally rice paddies, where it forms dense floating mats on the surface. It tolerates a broad range of 3.5–10 and thrives in water temperatures between 15–30°C, with optimal growth around 20–25°C under moderate light and nutrient availability. These conditions support its rapid vegetative proliferation in eutrophic, low-flow environments without prolonged freezing or extreme aridity. Fossil evidence links the to the Eocene , a period of prolific blooms in the approximately 49 million years ago that contributed to significant . However, the modern native range of A. filiculoides is limited to the , reflecting evolutionary divergence and post-glacial recolonization patterns. The species' is not threatened globally (USDA Forest Service, 2025).

Introduced Ranges

_Azolla filiculoides was first introduced to in the 1870s–1880s through the aquatic plant trade for use in aquariums and ornamental ponds, with early records in the . In , it was intentionally brought from in 1977 as a cold-tolerant substitute for the native in paddy green manuring. Introductions to began in 1948 as an aquarium plant in , while arrivals in and Pacific islands like occurred via similar ornamental and agricultural pathways in the mid-20th century. The species is now established across multiple continents outside its native American range. In , it occurs widely from to , with notable populations in the and , including West Georgia in the (first recorded in 2023). In , distributions include , , , and (first recorded in 2020), often linked to agricultural promotion. African records span sub-Saharan regions, including a 2021 documentation in Sudan's near Al Hideib village. In , it has naturalized in and , as well as in the Pacific. Human-mediated vectors have driven this global expansion. Intentional releases stem from agricultural trials as a and ornamental plantings in ponds and aquaria. Unintentional dispersal occurs via water plant trade, attachment to hulls and , and on machinery or clothing from infested sites. Fragments also spread naturally via waterfowl, amphibians, and . Azolla filiculoides prefers eutrophic, nutrient-rich waters with temperatures between 18–30°C for optimal growth. It exhibits frost limitation, though greater cold tolerance than related species allows overwintering in temperate zones. Warmer winters due to are enabling range expansion into cooler areas previously unsuitable for persistence.

Ecology

Symbiotic Nitrogen Fixation

_Azolla filiculoides forms a mutualistic symbiosis with the nitrogen-fixing cyanobacterium Nostoc azollae (formerly Anabaena azollae), which resides in specialized cavities on the dorsal lobe of the fern's leaves. These leaf cavities provide a protected, low-oxygen environment that supports the cyanobacterium's growth and activity. The symbiosis is obligate for the cyanobiont, which cannot survive independently outside the host due to genomic adaptations, including gene loss, that have occurred over millions of years of co-evolution. The mechanism of nitrogen fixation involves the enzyme , localized within specialized heterocysts that comprise 20-30% of the cyanobiont's cells in mature leaves. These heterocysts protect the oxygen-sensitive from inactivation by maintaining low internal oxygen levels through thick walls and respiratory activity. The fixed , primarily in the form of , is exchanged to the host , supplying up to the entirety of A. filiculoides' needs under nitrogen-limited conditions, while the provides carbohydrates—such as and —derived from its to fuel the cyanobiont's . This symbiosis is vertically inherited, with N. azollae transmitted from parent to via developing sporocarps, ensuring perpetual association without horizontal reinfection from free-living . Nitrogen fixation rates for A. filiculoides typically range from 30-60 kg N/ha per season, though higher yields of up to 128 kg N/ha in 50 days have been recorded under optimal conditions. The process is most efficient at temperatures of 20-30°C, where growth and activity peak. Fixation is inhibited by high concentrations, which downregulate (e.g., nifH), and elevated oxygen levels, which directly impair the enzyme despite protections. These factors highlight the symbiosis's sensitivity to environmental perturbations, limiting its efficacy in nutrient-rich or aerated waters.

Environmental Role and Interactions

Azolla filiculoides plays a significant role in aquatic ecosystems through various services, including oxygen production and . Its dense surface mats facilitate , contributing to oxygen release in the , which supports aerobic conditions in native . These mats can sequester at rates comparable to or exceeding those of many terrestrial plants, enhancing the carbon storage capacity of freshwater systems. Furthermore, the species provides for aquatic invertebrates, such as snails and larval amphibians, by offering and microenvironments within its floating cover. This role echoes the ancient during the Eocene around 49 million years ago, when massive blooms of ancestral Azolla species in the led to substantial atmospheric CO₂ drawdown through accumulation and . In terms of ecological interactions, A. filiculoides outcompetes in nutrient-enriched (eutrophic) waters by rapidly forming mats that limit light availability and nutrient access for algal growth, thereby helping to control excessive algal proliferation. It exhibits allelopathic effects through the release of , which inhibit the growth of competing aquatic plants and algae by disrupting their metabolic processes. While serving as a food source for waterfowl such as and geese, dense monocultures of the fern can reduce overall by shading out submerged vegetation and altering structure for other species. Recent research highlights A. filiculoides' contributions to , particularly in under warming conditions, where its rapid growth and symbiotic enable it to maintain in changing environments. A 2025 landscape genomics study of populations revealed three distinct genetic clusters, including one identified as A. filiculoides, demonstrating adaptive that supports its persistence amid regional climate shifts. Regarding pollution response, A. filiculoides accumulates such as lead, , and from contaminated waters, acting as a bioaccumulator to mitigate in aquatic systems. Studies from 2023 have shown its efficacy in of polycyclic aromatic hydrocarbons (PAHs), including and , through uptake, accumulation, and partial , achieving complete (100%) removal of these pollutants from contaminated water in experimental setups over 10 days.

Human Uses

Agricultural Applications

Azolla filiculoides serves as an effective in paddies, where it is inoculated into flooded fields to fix atmospheric through its with Anabaena azollae, contributing up to 60 kg N/ha upon . This practice, promoted in since the 1970s, enhances yields by 20–50% while reducing reliance on synthetic fertilizers, as demonstrated in field trials across , , and . In co-cultivation systems, A. filiculoides promotes growth beyond nitrogen supplementation by releasing metabolites such as peptides and into the , which roots absorb to alter the plant's and enhance accumulation. A 2025 metabolomics study revealed upregulated carbohydrates and in co-cultivated roots at 40 days, leading to increased tillering and height independent of inorganic . Similarly, aqueous extracts of A. filiculoides improve salt tolerance in ; 2024 trials showed that foliar or seed priming with the extract under 250 mM NaCl stress restored shoot by 15–25%, reduced oxidative damage via antioxidants, and upregulated stress-related genes like TaSOS1. As , A. filiculoides provides 25–30% crude protein on a basis, rich in essential , making it suitable for , , and to supplement conventional diets and improve growth rates. A 2025 analysis highlighted its integration into sustainable systems as a partial protein replacement, supporting growth in , , and . Cultivation for agricultural use involves inoculating ponds or fields with 1–2 kg/ha of fresh , allowing rapid doubling every 3–5 days under optimal conditions of 20–30°C and partial shade, followed by harvest after 30–40 days when biomass reaches 40–60 t/ha fresh weight. This method supports dual-purpose production for and feed, minimizing input costs in tropical and subtropical regions.

Biotechnology and Other Uses

Azolla filiculoides has emerged as a promising for production through anaerobic processes. In 2024, demonstrated that biological anaerobic of A. filiculoides yields as a clean source, with optimal pretreatment methods enhancing production efficiency. Pretreatment optimization, including thermal and chemical approaches, significantly improved yield and output by breaking down lignocellulosic structures, achieving up to 20-30% higher yields compared to untreated samples. These findings highlight the plant's potential in applications, leveraging its rapid growth and high accumulation. Recent studies have explored A. filiculoides as a sustainable feedstock for bioplastics, addressing the need for eco-friendly alternatives to petroleum-based . A 2024 review emphasized 's suitability due to its fast proliferation in aquatic environments, high nutrient content, and nitrogen-fixing symbiosis, which enable low-input cultivation for production. The biomass's and protein components can be processed into biodegradable films and composites, reducing environmental plastic waste while offering mechanical properties comparable to conventional bioplastics. Challenges such as scalability and extraction efficiency are noted, but its overall positions as a viable option for initiatives. In , A. filiculoides shows in heavy metal toxicity assessment and . A 2024 study evaluated its capacity to remove and lead, with spring-grown (green) variants exhibiting higher removal rates than autumn (red) types, achieving over 80% reduction in toxicity under controlled conditions. For , 2025 research confirmed its role in nutrient uptake, particularly and , in systems, improving through hyperaccumulation while generating usable . This dual benefit supports its application in integrated and pollution control. Beyond industrial uses, A. filiculoides serves ornamental purposes in aquariums and ponds, where its floating mats provide aesthetic cover and nutrient absorption. It also holds potential for drug remediation, as demonstrated by its ability to uptake and degrade antibiotics like sulphadimethoxine from contaminated waters. A 2025 review of its bio-functional properties further underscores applications, citing , , and protein-rich profiles suitable for functional foods and supplements.

Invasiveness

Spread and Ecological Impacts

_Azolla filiculoides spreads rapidly through , with biomass capable of doubling every 4–5 days under optimal conditions, allowing dense mats to form quickly on water surfaces. This growth is facilitated by fragmentation of fronds, which disperse via water currents, flooding, and human activities such as and equipment. Additionally, waterfowl contribute to long-distance dispersal by carrying fragments on their feathers or in their digestive tracts. , particularly elevated levels, further promotes expansion by enhancing nutrient availability in affected water bodies. The formation of extensive mats by A. filiculoides blocks penetration, suppressing growth of submerged aquatic plants and leading to their decline or local extirpation. These mats also reduce dissolved oxygen levels, often below 1 mg/L in underlying water, creating hypoxic conditions that harm , amphibians, and . diversity decreases significantly under mats, with fewer families and reduced abundances of groups like and compared to open water or vegetated areas. and populations are similarly diminished, altering webs and contributing to broader in invaded streams and wetlands. A 2022 assessment in highlighted these effects, noting over 50% reductions in oxygen and impacts on , , and , exacerbating degradation. Recent records indicate ongoing expansion in , including a 2021 documentation of A. filiculoides in the near Al Hideib village, , marking its invasive presence in that region. In and , CABI reports from 2023–2024 document persistent infestations, with increased distribution in eutrophic waterways across and parts of . Economically, A. filiculoides clogs waterways, impeding navigation and water flow, which affects fisheries by reducing access and habitat quality for fish stocks. It also diminishes recreational opportunities, such as boating and angling, leading to substantial management costs; in , unchecked infestations were estimated to cost £8.4–16.9 million annually in 2022, including losses to users and infrastructure. Globally, invasive aquatic plants like A. filiculoides contribute to broader economic damages, with restrictions on fisheries and recreation amplifying impacts in affected regions.

Control and Management

Prevention of Azolla filiculoides invasions primarily involves strict measures in to prevent accidental introductions via contaminated or , alongside campaigns to discourage intentional releases from ornamental ponds or . Monitoring eutrophic bodies, such as nutrient-enriched ponds and slow-flowing rivers, is essential for early detection, as the thrives in high-nitrogen environments and can rapidly form dense mats if unchecked. Physical control methods are suitable for small-scale infestations and include manual raking or the use of fine-meshed nets to remove floating mats, which should be disposed of away from water sources to prevent fragmentation and regrowth. Water drawdown, by lowering water levels to expose and dry out the plants, can also be effective in managed water bodies like reservoirs, though it requires careful planning to avoid downstream spread during refilling. Chemical control relies on aquatic-approved herbicides applied as post-emergence treatments to target visible fronds, with (e.g., formulation at 2% v/v) and (2-4 pints per surface acre) commonly used for spot treatments in spring to mid-summer when the is actively growing. These applications must follow label guidelines to minimize impacts on non-target aquatic life, and repeated treatments may be necessary due to the plant's rapid of 4-5 days. Biological control has shown promise through the introduction of the specialist Stenopelmus rufinasus, which feeds exclusively on species and has established populations in regions like the , , and since the early 20th century. A 2024 study assessed the economic benefits of this biocontrol, estimating annual management cost savings of up to £16.8 million for by reducing the need for mechanical or chemical interventions, particularly as warming enhances the weevil's efficacy. Integrated pest management approaches combine these methods with long-term strategies like reducing inputs from agricultural runoff to limit 's growth, alongside regulatory to curb spread. In , A. filiculoides is listed under Schedule 9 of the Wildlife () Order 1985, making it illegal to plant, cause to grow, or allow its spread in the wild, with ongoing monitoring to support compliance.

References

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