Here are some of the Riccia varieties I currently have. I've seen individual images here and there, but haven't seen one with all three species together. Hope you enjoy.
The left "Spiny" riccia is native of Thailand. The middle is the "Dwarf" riccia commonly seen here. The right is the common Riccia, also known as "Slender riccia".
Close up of the "Spiny" riccia.
Another with scale
Close up of the Dwarf riccia
Comparing individual leaf structure