Azolla mexicana

Species description

Care, breeding and tankmates

Plant profile

Placement

Midground

This is a strictly floating plant that spreads across the water surface. It should be used strategically to dim bright lights for sensitive shade-loving species below, or to provide cover for shy fish. In tanks where surface agitation is high, it should be contained within a floating corral to protect it.

Botanical form

Floating

This tiny fern features small, overlapping, bi-lobed leaves that repel water, allowing the plant to remain buoyant. The fronds are highly branched, creating a miniature, dense, fern-like structure floating on the surface. Fine, unbranched roots dangle beneath the plant into the water.

Growth

Medium

Its growth rate is incredibly fast, and it can quickly cover the entire surface of an aquarium if left unchecked. This rapid metabolism makes it an excellent candidate for nutrient export in tanks struggling with excess waste or algae. However, this means the aquarist must be prepared for weekly harvesting.

Substrate

None

This floating species does not root into any substrate, spending its entire life cycle on the water surface. Its short, hair-like roots are perfectly adapted to pull dissolved minerals and nitrogen directly from the aquatic environment. Substrate depth, composition, and nutrient content play no role in the successful cultivation of this fern.

Column fertilization

Recommended

Because its roots never touch the substrate, Azolla mexicana depends entirely on water column fertilization. Dosing a comprehensive liquid fertilizer will ensure it has the necessary micronutrients, particularly iron, to support its rapid growth and potential color changes. It is an excellent indicator of water column nutrient levels.

Root fertilization

None

Root tabs or nutrient-rich soils provide absolutely zero direct benefit to this species. All of its nutrient uptake occurs through its floating leaves and hanging roots directly from the surrounding water.

Trimming

Occasional

Traditional trimming is not required; instead, population control is achieved by netting or scooping out excess plants by hand. It is crucial to maintain open areas of the water surface to ensure proper gas exchange and allow light to reach submerged plants. Always dispose of excess Azolla responsibly to prevent environmental contamination.

Propagation

Division, Fragmentation

Propagation is entirely passive and occurs via vegetative fragmentation. As the plant expands, older sections break off naturally to form new, independent floating clusters. This process is continuous and rapid under favorable conditions.

Sensitivity

Moderate

Azolla mexicana is sensitive to being constantly submerged or splashed by strong filter returns, which can cause the leaves to rot. It also dislikes heavy condensation dripping from tight-fitting lids. It thrives in still or gently moving water with good air circulation above the surface.

Layout role

Floating

It functions primarily as a dynamic surface canopy that provides shade, shelter, and a natural aesthetic. The hanging roots create a visually interesting texture at the top of the tank and serve as a refuge for fry and small invertebrates. Its ability to change color offers a unique way to add red tones to the very top of an aquascape.