Multiple choice In which of these plants, sex organs are embedded in thallus? Moss Azolla Riccia Fern Reveal answer Fill a bubble to check yourself C Correct answer Explanation Riccia, a liverwort (Marchantiophyta), has a simple thallus body in which the sex organs (archegonia and antheridia) are embedded. In mosses, ferns, and Azolla, the sex organs are more distinctly structured rather than embedded in the thallus.