Any of a group of seed-bearing plants whose ovules are not enclosed in an ovary, but are exposed on the surface of sporophylls or similar structures. Each ovule may contain several eggs, all of which may be fertilized and start to develop in a process known as polyembryony. In most seeds, however, only a single embryo survives. The reproductive structures of many gymnosperms are arranged in cones. The gymnosperms do not form a distinct monophyletic grouping, but simply include all the seed-bearing plants that are not angiosperms. In addition to several extinct groups, there are four very diverse living gymnosperm phyla: the conifers, the cycads, the ginkgo (surviving in a single species), and the gnetophytes.