prothallium, the small, green, heart-shaped structure (gametophyte) of a fern that produces both male and female sex cells (gametes).

What is the function of the prothallus?

Prothallus is the gametophyte of the plant that is they are responsible for producing the gametes which are the male and female sex cells of the plants. These gametes fuse together to form the zygote.

Does the prothallium produce both egg and sperm cells?

Each prothallus produces gametes via mitosis. Meiosis is not needed because the cells are already haploid. Often, a prothallus produces both sperm and eggs on the same plantlet. While the sporophyte consisted of fronds and rhizomes, the gametophyte has leaflets and rhizoids.