The male reproductive structure of nonvascular plants is called an antheridium.

Here's why:

* Nonvascular plants include mosses, liverworts, and hornworts. They lack a vascular system for transporting water and nutrients.

* Antheridia are multicellular structures that produce sperm.

* Archegonia are the female reproductive structures that produce eggs.

Let me know if you have any other questions about nonvascular plants!