Fu Ping (Duckweed or Spirodela)

Chinese Herb Actions

Chinese Herb Dosage

• What is the typical dosage of Fu Ping?

  3–6 g in decoction, up to 9 g in severe cases — a deliberately restrained range, because the herb is a strong diaphoretic and the aim is a light sweat rather than a heavy one. The material is very light, so a small weight is a large volume of dried plant.

  • Internally: 3–6 g in decoction; up to 9 g where the presentation is severe.
  • Externally: the decoction is used as a wash for rashes and itching — a long-standing topical application of the same herb.
  • Because it is light and acrid, it is normally added late in the decoction rather than cooked at length.

  Source: Sacred Lotus dosage and notes records; published materia medica ranges, cross-referenced against multiple online sources. Reference only — not a prescription.

Chinese Herb Contraindications & Cautions

• Are there cautions for Fu Ping? Is duckweed safe?

  Fu Ping is contraindicated in exterior deficiency and in any profuse or spontaneous sweating. This is the central caution and it follows directly from the herb’s strength: it opens the pores forcefully, so in a patient who is already sweating, or whose defensive qi does not hold the surface, it drives further fluid loss. Our own record states this contraindication plainly.

  • Do not use where sweating is already excessive — spontaneous daytime sweating, night sweats from deficiency, or a weak, easily-chilled constitution.
  • Caution in the debilitated, the elderly and in pregnancy — strong diaphoretics deplete fluids; use belongs with a qualified practitioner.
  • Short courses — like other exterior-releasing herbs, it is used for the acute stage and then stopped, not taken long term.

  Sourcing note. Duckweed is grown in standing water, so buyers reasonably ask about contamination. What is actually documented is this: for Lemnaceae biomass used as food, the European Food Safety Authority concluded that the concentration of trace elements and contaminants in the material is highly dependent on cultivation conditions and fertiliser composition. That is a cultivation-practice finding about food-grade duckweed, and it is the correct reason to prefer a supplier with contaminant testing. It is not a report of contamination in medicinal Fu Ping, and the separate scientific literature in which duckweed is deliberately used to absorb metals from wastewater is phytoremediation research — a use of the plant as a clean-up tool, not a safety finding about the herb. No published contaminant survey specific to commercial medicinal Fu Ping was located.

  Source: Sacred Lotus cautions record; published materia medica; PMID 34815779 (EFSA opinion on water lentil powder from Lemnaceae — contaminant levels depend on cultivation conditions). Neutral reference facts, not usage instructions.

Chinese Herb Toxicity & Overdose

• Low. Fu Ping is not classified as a toxic herb in the Chinese materia medica and our record does not flag it as toxic or endangered. Duckweeds are edible plants: several Lemnaceae species are eaten as vegetables in South-East Asia, and duckweed powder has been assessed formally as a food. The practical risks attach to over-sweating at high dose and to raw-material quality, not to intrinsic toxicity. In the food-safety assessments, the noted issues were manganese intake at food-ingredient levels and the potential for allergic reaction to a high-protein plant material — findings about daily food-quantity consumption, not about short-course herbal decoction.

  Source: Sacred Lotus herb record; PMID 34815779 and PMID 34987622 (European food-safety assessments of duckweed/water-lentil powders). Reference note, not a safety guarantee.

Herb-Drug Interactions

• No established clinical herb–drug interactions are documented for Fu Ping. No interaction case reports or clinical pharmacokinetic studies were located. On mechanism alone, a strong diaphoretic and mild diuretic warrants ordinary caution alongside diuretic therapy or in anyone at risk of dehydration or electrolyte disturbance — that is precautionary reasoning, not a demonstrated interaction. Patients on prescription medication should confirm use with their prescriber and a qualified practitioner.

  Source: PubMed search of the Spirodela polyrhiza literature (no clinical interaction reports located); mechanism-based precaution. Reference note.

Western / Biomedical Research

Chinese Herb Clinical Studies & Research

Provided as research context — a summary of published biomedical study, not a therapeutic or medical claim.

• Is there modern research on Fu Ping (Spirodela polyrhiza, duckweed)?

  Yes — a consistent preclinical anti-allergic and anti-inflammatory line of work that lines up unusually well with the traditional rash indication, but no clinical trials. The most specific finding: a duckweed extract and its flavonoid constituent vitexin inhibited the ORAI1 calcium-release-activated calcium channel, reducing mast-cell degranulation and T-cell activation — a plausible mechanism for an anti-itch, anti-rash effect. Separate work found the extract also modulates TRPV3, another channel implicated in itch and skin barrier signalling.

  • Topical skin models — topical application of Spirodela polyrhiza improved atopic-dermatitis-like disease in mice, and a duckweed-containing combination extract alleviated dermatitis in a chemically induced murine model by shifting immune balance and improving skin barrier function. Animal models only; note the parallel with the herb’s traditional use as an external wash.
  • Contact dermatitis — extract reduced inflammation in a mouse contact-dermatitis model, with active compounds and molecular targets identified.
  • General anti-inflammatory activity — ethanolic extract suppressed lipopolysaccharide-induced inflammation in cultured macrophages.
  • Human evidence — none located. No randomised trials of Fu Ping were found.

  Context, clearly separate from medicinal use: Spirodela polyrhiza is one of the most intensively studied plants in two unrelated fields. It is developed as a fast-growing protein crop — duckweed powders have been formally evaluated as novel foods in the EU — and it is widely used in wastewater phytoremediation, where its capacity to take up metals and industrial pollutants is the point of the research. Those metal-uptake papers describe the plant deployed as a clean-up organism in contaminated water; they are not measurements of medicinal Fu Ping and must not be read as safety findings about the herb.

  Sources: PMID 30149756 (vitexin / ORAI1 channel inhibition, anti-allergic, preclinical); PMID 28290212 (Orai1 and TRPV3 modulation, mast-cell degranulation, preclinical); PMID 26778605 (topical application in atopic dermatitis, animal model); PMID 33571899 (combination extract in a murine atopic-dermatitis model); PMID 37686078 (contact dermatitis in mice, active compounds and targets); PMID 22303922 (anti-inflammatory activity in LPS-stimulated macrophages); PMID 34815779 and PMID 34987622 (duckweed as a novel food); PMID 36657596 and PMID 38492385 (wastewater phytoremediation — environmental context, not pharmacology). Research context, not a therapeutic claim.

Chinese Herb Notes

• How does Fu Ping differ from other rash-venting and exterior-releasing herbs?

  Fu Ping is the most strongly sweat-inducing of the cool, acrid exterior herbs, and it uniquely combines venting rashes with promoting urination. That double action — outward through the pores and downward through urine — is what sets it apart from its usual comparisons.

  • Bo He (field mint) — also cool, acrid and rash-venting, but lighter and more aromatic, with a Liver-soothing dimension; it does not move water.
  • Chan Tui (cicada moulting) — the other well-known rash-venting herb for wind rash and itching; it also brightens the eyes and settles wind, but is not a strong diaphoretic.
  • Ma Huang — the comparison usually drawn for the diaphoretic-plus-diuretic combination, but Ma Huang is warm and used for wind-cold. Fu Ping is often described as the cold-natured counterpart for the same mechanical job in a heat pattern.

  Topical use: our own record notes it may be used externally as a wash for rashes, which is consistent with its rash-venting indication.

  Note on the botanical name: our record gives the pharmaceutical Latin as Herba Lemnae Seu Spirodelae — literally “herb of Lemna or Spirodela” — reflecting the older practice of accepting either genus. Contemporary Chinese pharmacopoeial practice defines Fu Ping specifically as Spirodela polyrhiza (giant duckweed), and essentially all modern research on the herb uses that species. Duckweeds are a closely related group of floating aquatics, so this is a scope-of-species question rather than a substitution error. The identity field is left unchanged pending owner review.

  Source: Sacred Lotus herb record (Latin, notes, topical use); published materia medica differentiation (Bensky; Chen & Chen), cross-referenced against multiple online sources; species scope per the modern research literature (see research). Traditional differentiation, not treatment advice.