Waterweed

Egeria densa

Also known as Anacharis, Brazilian waterweed, Elodea densa, Egeria

FreshwaterBrackishStemCuttingsSide shoots

Invasive. Invasive and regulated in parts of the US and other regions. Never release into the wild; dispose of in the trash.

Waterweed (Egeria densa) — Lara Gudmundsdottir · CC BY-SA 4.0

Care at a glance

Light: Medium light
CO2: No CO₂ needed
Growth rate: Fast
Placement: Background
Type: Stem
Temperature: 59–82°F (15–28°C)
pH: 6.5–7.9
Hardness: 4–18 dGH
Max height: 39.4 in (100 cm)
Spread: 5.9 in (15 cm)
Nutrient uptake: Water column
Growth region: Submersed
Difficulty: Beginner
Origin: South America (Brazil, Argentina, Uruguay)
Family: Hydrocharitaceae

Overview

A classic beginner background plant that grows fast in moderate light with no CO2. Plant individual stems a couple of centimeters into the substrate with a little spacing, stripping the lower leaves from the bottom 5 cm first, or simply let bunches float. It tolerates low light but stretches leggy and pale there, so moderate light keeps it bushy and bright green. It is a heavy water-column feeder, so a bit of liquid fertilizer keeps it from going stringy. Top it regularly and replant the cuttings to keep it dense, and note that it can react to a tank move by dropping leaves before regrowing.

In the wild

Native to slow-moving and still fresh water in southeastern South America, across Brazil, Argentina, and Uruguay. It grows fully submersed as a rooted stem plant in lakes, ponds, and sluggish streams. Thanks to the aquarium and pond trade it has naturalized worldwide and is a notorious invasive weed in many temperate regions, which is why some sources label it cosmopolitan.

Good to know

A stem plant in the Hydrocharitaceae, long sold under the older name Elodea densa, and still widely traded as Anacharis. It grows in dense whorls of three to six small leaves around a long brittle stem and roots from the lower nodes, though it draws most of its nutrition straight from the water. In the trade nearly all plants are male clones, so it rarely if ever sets seed in cultivation.

Did you know

It is one of the standard plants used in school biology classes to demonstrate photosynthesis, since a cut stem in bright light visibly releases a stream of oxygen bubbles from the stem.