prothallus
/proʊˈθæləs/
noun
- The small, flat, heart-shaped structure that grows from a fern spore and produces the sex cells for reproduction (same as prothallium).
- Each prothallus contains both male and female reproductive organs.
- The prothallus is the first stage of growth after a fern spore germinates.
- A prothallus can be seen with a magnifying glass on the surface of damp potting soil.