The gamete-producing haploid form of the green alga Ulva is known as a gametophyte.

Here's why:

* Ulva exhibits an alternation of generations life cycle, meaning it has two distinct phases:

* Sporophyte: The diploid phase, producing spores through meiosis.

* Gametophyte: The haploid phase, producing gametes (sperm and egg) through mitosis.

* Gametophytes are multicellular and haploid, meaning they only have one set of chromosomes.

* In Ulva, the gametophyte is the dominant phase, meaning it is larger and more easily observed than the sporophyte.

Let me know if you have any other questions!