Common Duckweed vs Giant Crypt

They do not overlap much in exact placement, which is why this comparison is more about adjacent options than true one-for-one replacements.

Common Duckweed is a floating plant that usually reaches about 0.2 cm tall by 1 cm wide. Giant Crypt is a rosette / crown plant that usually reaches about 70 cm tall by 30 cm wide.

They also share practical benefits such as surface cover and grazing surfaces, so the decision is not only about looks.

The strongest overlap signals are practical: they offer many of the same practical benefits, including provides surface cover and good grazing surface.

Choose Common Duckweed when its exact growth habit fits the open space you have and you want the finished scape to lean toward its shape, texture, or spread.

Common Duckweed is the tidier fit when space is limited.

Common Duckweed gives denser visual cover when fish security matters more.

Common Duckweed also suits keepers who want low light and no added CO2, with fast growth, high maintenance, and beginner difficulty.

Choose Giant Crypt when its shape, mature size, or planting style gives the scape a cleaner finish than forcing Common Duckweed into the same role.

Giant Crypt gives you more propagation flexibility through runners / stolons and rhizome division.

Giant Crypt fits a routine built around low light and no added CO2, with slow growth, low maintenance, and beginner difficulty.

Role overlap lands at 12/100 and care similarity lands at 68/100. Treat those numbers as a shortcut for the decision, not as a replacement for looking at mature size and placement.

Common Duckweed is free-floating with no substrate required and feeds mainly as a water column feeder. Giant Crypt is rooted in substrate with nutrient-rich substrate preferred and feeds mainly as a root feeder.

Their mature height diverges enough that they stop being true one-for-one replacements.

If the tank already has several demanding plants, the easier choice is the one that matches your existing light, CO2, and trimming routine.

If you need a true substitute, keep looking. This pair is more useful as a contrast because the plants ask for different layout decisions once they mature.

A practical way to decide is to imagine the tank six months from now. The better plant is the one that still fits the same space after several trims, not the one that only looks right on planting day.

Common Duckweed and Giant Crypt look like a comparison pair on the surface, but they usually serve different jobs in a planted tank. The smarter decision is to start from the layout problem you are solving, then choose the plant that belongs in that role instead of comparing them as direct substitutes.