Marimo moss ball

Aegagropila linnaei

Also known as Marimo, Moss ball, Lake ball, Cladophora ball, Cladophora aegagropila

FreshwaterMossRhizome division

Marimo moss ball (Aegagropila linnaei) — コムケ at Japanese Wikipedia · CC BY-SA 3.0

Care at a glance

Light: Low light
CO2: No CO₂ needed
Growth rate: Slow
Placement: Foreground
Type: Moss
Temperature: 39–82°F (4–28°C)
pH: 6.0–8.5
Hardness: 2–18 dGH
Max height: 3.9 in (10 cm)
Spread: 3.9 in (10 cm)
Nutrient uptake: Water column
Growth region: Submersed
Difficulty: Beginner
Origin: Lakes and slow rivers of Northern Europe, Japan, and scattered cool temperate regions (notably Lake Akan, Japan and Lake Myvatn, Iceland)
Family: Pithophoraceae

Overview

About the easiest 'plant' you can keep. It sits on the substrate in the foreground or midground with no planting, attaching, or trimming needed, and takes any light level with no CO2 or dosing. Growth is glacially slow (a few mm per year), so it stays put. Roll it gently now and then to keep the round shape and to clear debris and detritus from the underside, and prefer cooler water since heat above the high 20s C can brown it.

In the wild

Native to cool, clear lakes and slow rivers across Northern Europe and Japan, with scattered populations elsewhere. The famous spherical 'lake ball' growth form develops in only a few lakes where gentle wave action rolls loose filaments into velvety green balls. It is strictly protected and considered endangered at its best-known sites, including Lake Akan in Japan and Lake Myvatn in Iceland.

Good to know

Despite the 'moss ball' name, Aegagropila linnaei is not a moss or a plant at all. It is a filamentous green alga in the order Cladophorales (family Pithophoraceae). The ball is a colony of branching filaments radiating from the center, and the same alga also grows as free filaments or flat mats on rocks in the wild.

Did you know

Did you know marimo balls float and sink on a daily rhythm? Photosynthesis traps tiny oxygen bubbles in the velvety surface during the day, lifting them toward the light, and they settle back down at night as the bubbles escape.