Propagating Watermeal (Wolffia arrhiza)
How to propagate Wolffia arrhiza, the world's smallest flowering plant: rootless floating grains that bud daughters and double in days, plus how to keep them in check.
Overview
Wolffia arrhiza, known as watermeal, is the smallest vascular flowering plant on Earth. Each individual is a rootless, roughly spherical green frond about 1 mm wide with a flat top that lets it float at the water surface. It thrives in quiet, still water and behaves as a mixotroph, gaining energy from photosynthesis or by absorbing dissolved carbon from the water.
Propagation Method
Watermeal propagates almost entirely by vegetative budding rather than from cuttings or seed. The rounded body of each grain buds off a new individual, and this division repeats continuously. Under good conditions the population can double in less than four days, forming a dense floating mat over the surface.
Step-by-Step
- Start with a small clean clump of healthy floating grains skimmed from an established surface.
- Place the grains on the surface of still or very gently moving water so they can float freely.
- Provide medium light and a few free nutrients; the grains begin budding daughter individuals on their own.
- Allow the mat to spread; harvest or thin a portion every 3 to 4 days as the colony doubles.
- Move skimmed grains to a new container or tank to establish a fresh culture.
Conditions for Healthy Growth
- Temperature 18-28 C; in cooler water the plant goes dormant and sinks to overwinter.
- Medium lighting at the surface.
- Calm, still water with little surface agitation.
- Low nutrient demand; a small amount of dissolved nutrients is enough.
- No CO2 supplementation required.
Maintenance
Because the mat doubles every few days, skim and remove excess grains roughly weekly to keep light reaching plants below. Harvested watermeal is highly nutritious and can be fed to many fish, which also helps keep the colony in balance.