Just similar to many controversial things, the quick-growing common duckweed, also known as Spirodela Polyrhiza and Fu Ping, has dual nature. In other words, this green floating plant can be welcomed or invasive, which depends on where it is placed – it can be an excellent green feed to fish in clear water but a disaster to the water area and its ecological system in nutrient rich water. Likewise, duckweed can be a good or bad Chinese herb, which is up to how it is used by the herbalist. For more information about how to make full use of health benefits of the duckweed, read on please.
Common duckweed facts and description
This is a tiny lightweight green floating spermatophyte. Common duckweed habitats are ponds, wetlands, paddy fields, arm of lake, or any other places that have still water bodies. It is better known as Spirodela polyrrhiza (L.)Schleid. [Lemna polyrrhiza L.] or Lemna minor L. in scientific name and Latin name. And other duckweed common name include lesser duckweed, Least Duckweed, spirodela polyrhiza or spirodela polyrhizae, giant duckweed, ducksmeat, herba spirodelae, and more. In TCM this herb refers to its dried whole plant, usually harvested from June to September. Prior to the medical use, it needs to remove impurities and be dried in the sun. Medicinally this herb is produced from swamps across the China, mainly including Hubei, Jiangsu, Zhejiang, Fujian, Sichuan, and other provinces.
Medicinal duckweed is a flat thallus, which is oval or orbicular-ovate, and 2 to 5mm in diameter. Upper surface is light green to gray green and with a small depression on one side and neat or slightly curled edge. Lower surface is purple green to purple brown and with several fibrous roots. It is lightweight and brittle. It has slight odor and thin flavor.
Main chemical constituents of spirodela polyrhiza include orientin, luteolin-7-monoglycoside, vitexin, malonylcyanidin-3-monoglucoside, β-carotene, lutein, epoxy-lutein, violaxanthin, neoxanthin, 8% lipid, and 24.4% protein. And Lemna minor L. contains trans-1, 3-phytadiene, lycopersene, sitosterol, phytol, 4(R)-4-hydroxyisophytol, (10R)-hydroxyhexadeca-7Z, 10Z, 13Z-trienoic acid, 11Z-hexadecenoic acid, and 7Z, 10Z, 13Z-hexadecatrienoic acid.
Common uses for duckweed
Duckweed is an aquatic plant in the family Araceae. It grows pretty fast. According to relevant research, its growth rate is about 64 times of maize. What’s more, its fronds contains large amounts of starch, up to 75% of the dry weight in cultivated species or 30% in wild species, which make it one of the best potential bio-energy crops. In addition, its high protein content also makes it become a new source for feed industry. It is more commendable that this floating plant can be grown in wastewater that comes with high that in high nitrogen and phosphorus content. As a result, it is a fine bioremediation species thanks to its ability of absorbing nutrients from sewage. More importantly, it is a really amazing herb that can cure a number of complaints, which now can be justified by the modern pharmacology.
Modern pharmacological actions of duckweed
1. Diuretic effect. The active ingredients of diuresis are potassium acetate and potassium chloride;
2. Cardiovascular effects. Its water extracts showed strengthening effect on the quinine-induced heart failure in frog. Calcium can enhance this effect. Its large dose can make the heart stop in diastole and cause rising of blood pressure by contracting blood vessels;
3. Antipyretic effect. It was proved with a weak antipyretic effect by administering orally with 2g/kg decoction and infusion to feverous rabbit caused by injected with mixed typhoid vaccine;
4. Other effects. Both of its antibacterial and antimalarial experiments were negative. And it killed Culex larvae and pupae in the laboratory and field.
Proven duckweed related herbal remedies
This herb, listed as medium-grade drug in “Shen Nong’s Herbal Classic”, is commonly used in Traditional Chinese medicine (TCM). It is acrid in taste and cold in properties. And it covers meridians of lung and bladder. Basic functions are relieving exterior syndrome by diaphoresis, promoting eruption to relieve itching, inducing diuresis to alleviate edema, and clearing heat and removing toxicity. Major duckweed uses and indications include wind-heat exterior pattern, measles without adequate eruption, rubella itching, edema, retention of urine, sores and ringworm, erysipelas, burns, and so on. Recommended dosage is from 3 to 9 grams in dried herb or 15 to 30 grams in fresh herb.
1. Wind-heat type common cold. This herb is acrid, cold, lightweight, and floating in nature, which endowed it with the function of coursing wind and dissipating heat. So it is ideal for treating anemopyretic cold accompanied with fever but without sweating, in which common duckweed usually combines with Bo He (Mentha), Chan Tui (Cicada Moulting), Lian Qiao (Forsythia Fruit), and so on. In the case of wind-cold type common cold, manifested as aversion to cold but without sweating, it should work with wind-cold-effusing medicinal like Ma Huang (Ephedra), Xiang Ru (Aromatic Madder), Qiang Huo (Notopterygium Root), and more.
2. Measles that fail to erupt. It is usually used along with Mentha, Cicada Moulting, Niu Bang Zi (Arctium) for the beginning of measles that fails to erupt.
3. Rubella itching. In the case of wind-heat pattern, it is generally used with Mentha, Cicada Moulting, Arctium, or other acrid-cool type herbs that dispel wind and relieve itching. In the case of wind-cold pattern, it is commonly used together with Ephedra, Fang Feng (Ledebouriella Root), Jing Jie (Schizonepeta Stem), or any other acrid-warm herbs that dispel wind and relieve itching.
4. Edema and oliguria. It is good at treating edema and oliguria accompanied with wind-heat exterior pattern. In this case, it can be used alone or together with Ephedra, Forsythia, Dong Gua Pi (Winter Melon Peel), and so on.
Potential common duckweed side effects and contraindications
According to statistics, adverse reaction and drug interactions about common duckweed were rarely reported. However, TCM doctors believe that it shouldn’t be used in the case of spontaneous perspiration due to exterior deficiency.