The answer to this is they evolved after the seedless vascular plants.
Gymnosperm, or sometimes termed as seed plants, are classified as vascular plants and has been thriving for centuries on earth though producing seeds. they are multicothyledonous and are the opposite of flowering plants. Conifers would be the most abundant group of gymnosperm while the cycads come in second. Gingko would place last with just having one species under its name.
