Which type of gymnosperm has the least amount of species diversity on Earth today?

cycad

ginkgo

gnetophyte

conifer

Ginkgo has the least amount of species diversity out of all gymnosperms.

The cycads, gnetophytes, and conifers have many genera and various species, but there is only one species in the one sole Ginkgo genus, the Gingko biloba.

The Gingko biloba presents the only surviving species of a previously widespread and diverse spread genus Ginkgo.