Wolffia arrhiza

Wolffia arrhiza is an aquatic plant which grows in quiet water bodies such as ponds. The green part of the plant, the frond, is a sphere measuring about 1 mm wide, but with a flat top that floats at the water's surface. It has a few parallel rows of stomata.[3] There is no root. The plant produces a minute flower fully equipped with one stamen and one pistil. It often multiplies by vegetative reproduction, however, with the rounded part budding off into a new individual.[3][7] In cooler conditions the plant becomes dormant and sinks to the bed of the water body to overwinter as a turion.[8] The plant is a mixotroph which can produce its own energy by photosynthesis or absorb it from the environment in the form of dissolved carbon.[4]

This tiny plant is a nutritious food. Its green part is about 40% protein by dry weight and its turion is about 40% starch.[9][10] It contains many amino acids important to the human diet, relatively large amounts of dietary minerals and trace elements such as calcium, magnesium, and zinc, and vitamin B₁₂.[10] It has long been used as a cheap food source in Myanmar, Laos, and Thailand, where it is known as khai-nam ("eggs of the water").[11] The plant is prolific in its reproduction, growing in floating mats that can be harvested every 3 to 4 days; it has been shown to double its population in less than four days in vitro.[12]

It is also useful as a form of agricultural and municipal water treatment.[13] It is placed in effluent from black tiger shrimp farms to absorb and metabolize pollutants.[14] The plants grow quickly and take up large amounts of nitrogen and phosphorus from the water.[9] The plants that grow in the wastewater can then be used as feed for animals, such as carp,[15] Nile tilapia,[16] and chickens.[8]

Wikimedia Commons has media related to Wolffia arrhiza.

• Jepson Manual Treatment
• USDA Plants Profile