The fossil of a plant reveals that it produced spores that were used for reproduction. Which type of plant was it seed

It was a non-seed-bearing plant, or sporophyte, such as a moss, liverwort, or hornwort.

Explanation:

All plants have spores as part of their life cycle (alternating between sporophyte, which is asexual, and gametophyte, which uses sexual reproduction), but because the spores of this fossilized plant were used for reproduction, this plant most likely did not produce any seeds.