Question

1. which category of gymnosperm is recognized by only a single species? conifers cycads gnetophytes ginkgo

Explanation:

Ginkgo is a category of gymnosperm recognized by only a single species, Ginkgo biloba. Conifers have many species (e.g., pine, fir). Cycads have multiple species too. Gnetophytes also have more than one species.

Answer:

ginkgo