Definitions

1. noun

The male or hermaphroditic sex organ of a fern or other cryptogam, which bears the antheridia.

“The prothallus of the fern plant is where the fertilization process begins.”

2. noun

A similar sex organ in other plants, such as a moss or liverwort, which also bears the antheridia.

“In certain species of moss, the prothallus is the site of gamete fusion.”