Wolffia (khai nam): the smallest flowering plant, grown in a tub as a vegetable

Khai nam, also called pham (Wolffia globosa), is the world’s smallest flowering plant: a green grain under 1 mm across that floats on the water with no roots. People in northern and northeastern Thailand, Laos and Myanmar have long eaten it as a vegetable. Recent research is interested in it because it grows very fast and is high in protein by dry weight.

But the same trait that makes it grow so fast, pulling everything it can out of the water, makes the water you grow it in the most important thing of all. This lesson covers what the nutrition numbers really say, how to grow it in a container, and how to eat it safely.

Nutrition numbers: read the basis

Almost every protein figure for khai nam is per dry weight. Fresh khai nam is 96.51% water, as measured in a Chiang Mai University study. Reported values vary with where and how it was grown.

Sample	Protein (% dry weight)	Notes
Organic farm, San Pa Tong, Chiang Mai (2025)	20.2	fat 4.5%, ash 15.2%
Natural pond, Sakon Nakhon (Chulalongkorn, 2011)	33.3	complete essential amino acids
Circulating-water tank (Chulalongkorn, 2011)	48.2	the highest-yielding system tested
Mankai strain, closed system, Israel	about 45	a commercially cultivated strain

The Chiang Mai paper cites earlier work giving 17-45% protein by dry weight. The main essential amino acids in its sample were lysine, leucine and phenylalanine.

About vitamin B12

B12 normally comes from animal foods. A 2020 study in Nutrients measured B12 in the Mankai strain, grown in a closed, controlled system, at about 2.8 µg per 100 g dry weight, in forms the body can use rather than inactive look-alikes. In an 18-month trial with 294 participants, the group whose green Mediterranean diet included a daily 100 g khai nam shake saw serum B12 rise 15.4%, against 5.2% in the control group.

Limits the researchers state themselves:

• They don’t know where the B12 in the plant comes from; it may come from bacteria living in it.
• Participants started with normal B12, so the study can’t say whether it helps people who are deficient.
• The plant’s effect could not be fully separated from the rest of the diet.
• The company that grows Mankai was part of the research team.

This result belongs to one strain grown under controlled conditions. There is no equivalent data for khai nam from a pond or a backyard tub. Don’t use it to replace a B12 source your doctor recommends.

Worked example: protein in 100 g of fresh khai nam

Using the Chiang Mai figures, step by step:

1. 100 g of fresh khai nam at 96.51% water leaves 100 × 0.0349 ≈ 3.5 g of dry matter.
2. At 20.2% protein by dry weight, that is 3.5 × 0.202 ≈ 0.7 g of protein.
3. A sample at 48.2% protein would give 3.5 × 0.482 ≈ 1.7 g.

For comparison, the researchers say 100 g of frozen Mankai equals about 20 g of dry matter and gives about 0.5 µg of B12, roughly 21% of the adult daily recommendation of 2.4 µg. That dry-matter ratio describes their product, not fresh khai nam scooped from a tub.

A 100 g portion of fresh khai nam carries modest protein. Treat it as one vegetable in the meal, not a meat replacement.

Growing it in a tub or basin

From a Chulalongkorn University thesis on the best conditions for growing khai nam:

• Wide beats deep. Khai nam floats on the surface, so yield depends on surface area.
• Sun. Strong midday light did not reduce its photosynthesis, but water reaching 40 °C reduced it significantly. A small container in full sun heats fast, so give it afternoon shade or a shade net.
• Water pH. The best range was 5-7.
• Starting density. Cover 5-20% of the surface; 15% gave the best result in the trial.
• Speed. In natural conditions one generation takes about 4 days.
• Season. In the natural pond in Sakon Nakhon, biomass peaked in July and was lowest in February.

A back-of-envelope example: start at 15% cover and, if everything were ideal and it doubled every 4 days, you would have 30% on day 4, 60% on day 8, and full cover around day 11-12. Real growth is always slower, because light, temperature and nutrients are never perfect every day. Once the surface is full, scoop it with a fine sieve and leave about 15% to grow the next round.

The water needs some nutrients or growth stalls. Use the same idea as simple Kratky hydroponics: a dilute nutrient solution in clean water. Don’t use fresh, uncomposted manure water, which raises the risk of germs, and cover the tub with mosquito mesh so mosquitoes can’t lay eggs.

Clean water, because khai nam absorbs everything

Khai nam takes up dissolved substances straight from the water. Researchers use it to treat wastewater and have found it accumulates cadmium and arsenic from polluted water. The Chiang Mai organic-farm sample passed every limit in Thailand’s Ministry of Public Health Notification No. 414, but arsenic measured 2.00 mg/kg dry weight, exactly at the 2.0 ceiling.

So even from a well-run farm, the numbers can sit close to the line. If you grow your own:

• Use tap water, or rainwater collected in a clean container.
• Never use canal water, drain water, or water that has run off sprayed fields.
• Don’t place the tub under a gutter that drains a dirty roof or yard.
• Rinse several times in a fine sieve, then cook it through.

Common mistakes

• Reading 40% protein and assuming fresh khai nam has 40% too. Fresh khai nam is nearly all water.
• Scooping khai nam from a pond or canal of unknown origin. You can’t know what that water has passed through.
• A small basin in blazing sun. The water heats until growth stops.
• Harvesting the whole tub. Leave a starter for the next round.
• Leaving still water uncovered. It becomes a mosquito nursery.

Sources

• Bioactive Potential of Protein Extracts Derived from Dried Wolffia globosa — Molecules (MDPI), 2025
• Wolffia globosa–Mankai Plant-Based Protein Contains Bioactive Vitamin B12 and Is Well Absorbed in Humans — Nutrients (MDPI), 2020
• Optimal conditions for production of Khai-Nam Wolffia globosa — Chulalongkorn University thesis (NRCT DOI)