Here's why:

* Green algae are not plants. They are a type of protist, a kingdom of organisms that are mostly single-celled and have a simple structure compared to plants.

* Seeds are produced by flowering plants (angiosperms) and gymnosperms. These plants have complex reproductive systems that involve flowers, cones, and the development of embryos within seeds.

* Green algae reproduce asexually and sexually, but not through seeds. They reproduce through spores or by cell division.

So, while green algae are photosynthetic and resemble plants in some ways, they don't produce seeds and are classified as a different type of organism.