Riccia fluitans: a floating liverwort, by the grower data

What the grower data says

Tropica rates Riccia medium on difficulty, light and CO2, with medium growth ^[1]. Aquasabi agrees on medium difficulty and medium light, rates growth fast and lists CO2 as required ^[2]. Tropica’s description says it thrives best with added CO2, and that in good conditions small oxygen bubbles form on the leaf tips ^[1]. Its fertilizer guide puts plants in the medium group at roughly 10–15 mg/L of CO2 ^[4].

Two ways to grow it

Riccia is sold for two quite different uses.

• Floating. Tropica calls it a traditional floating plant ^[1], and Aquasabi lists it for the water surface and as a spawning plant ^[2].
• Submerged on stone. Tropica credits Takashi Amano with inspiring aquarists to keep it submerged ^[1]. The method is to tie it to a stone with fishing line. The catch is that new shoots always grow toward the surface, so it has to be pruned with scissors to stay put ^[1].

Either way it has no roots in the substrate. Tropica’s fertilizer guide points out that moss and floating plants can only be fed through the water ^[4].

Compared with other surface plants

Among the floating and moss-like plants profiled on this site, Riccia is the demanding one ^{[1, 5]}:

Plant	Difficulty	Light	CO2
Riccia fluitans	Medium	Medium	Medium
Limnobium laevigatum	Easy	Low	Low
Taxiphyllum barbieri ‘Bogor Moss’	Easy	Low	Low
Aegagropila linnaei	Easy	Low	Low

Of the four, only Riccia carries medium ratings for light and CO2, and Tropica’s description adds that it thrives best with added CO2 ^[1].

Size

Tropica describes it as 1–5 cm tall, with a height rating of 3–5 cm or more ^[1]; Aquasabi gives a care height of 1–5 cm ^[2].

What kind of plant it is

Riccia is a liverwort. Tropica’s type field files it under “Moss”, but its own description calls it a “cosmopolitic liverwort” ^[1]. The GBIF Backbone Taxonomy accepts Riccia fluitans L., a name Linnaeus published, in the family Ricciaceae, order Marchantiales, in the liverwort phylum Marchantiophyta ^[3]. Liverworts and mosses are both non-vascular plants, outside the scope of the World Checklist of Vascular Plants, so this profile has no WCVP record. Tropica’s origin field reads “Cosmopolitan” ^[1].