Currently, there are 4 growth forms of "riccia" in the hobby, but only three are likely to be of different species. The other is simply a variation due to growing conditions.cminghan said:maybe i will replace it with some "dark green" riccia,can anyone tell me the actual name for "dark green" riccia...
(1) Riccia fluitans: this species has large floating thalli that are colored light green.
(2) Riccia sp. 'Dwarf' - this species has small floating thalli that are colored light green.
(3) Riccia sp. 'Dark' - this species has large floating thalli that are colored medium green. It typically appears among the R. sp. 'Dwarf', which makes me wonder if it is of a different species at all.
(4) "Sinking Riccia" - this growth form has sinking thalli that are colored dark green. Its size is dependent on which of the above species has been subjected to growing conditions that induce the sinking behavior. Typically, one can induce riccia to sink by cultivating it in very low light. Once placed under good light, it often reverts back to the floating form.
So to answer your question Ming Han, your "dark green" riccia can be either (3) or (4), depending on if the thalli sink or float. If they float and you discovered them among your R. sp. 'Dwarf' carpet, then more likely than not, it is Riccia sp. 'Dark', a name I just made up to distinguish it from the other three :biggrin:.