Unlike many of our species of Riccia, R. crystallina can be quite large, with rosettes growing to 2-3 cm in diameter. They are often much smaller though.
It can be surprisingly abundant, forming dense concentrations of hundreds or even thousands of rosettes in a small area. It is sometimes also a member of an interesting bryophyte community which may also include Sphaerocarpos michelii and Bryum gemmilucens.
Read the Field Guide account