Within the large plant kingdom, not all species produce flowers, known collectively as angiosperms. Plants lacking flowers but producing cones or strobili are called gymnosperms. The word "gymnosperm" translates to mean "naked seed." Gymnosperm seeds do not develop inside an ovary, as in the case of flowering plants. Botanists don't regard ferns, which reproduce with spores, as gymnosperms. Instead, ferns are considered vascular, non-flowering plants.
Around 550 species of conifer trees exist worldwide and make up the largest group of gymnosperms. Conifers may be evergreen or deciduous. Examples of evergreen conifers include pines (Pinus spp.), firs (Abies spp.), cedars (Cedrus spp.), spruces (Picea spp.), junipers (Juniperus), hemlocks (Tsuga spp.) and yews (Taxus spp.). Their cones may be hard and dry, such as with pine and spruce trees, or fleshy, like with junipers. Some conifers lose their needles or scaly leaves in winter, as in the case of larches (Larix spp.) and cypresses (Taxodium spp.). Conifers tend to inhabit colder and drier habitats around the world.
Found primarily in the warmer climates of the world, cycads comprise the next largest group of gymnosperms. Cycads more widely existed during the times of the dinosaurs as evidenced in fossil records. Cycads look like miniature palms or massive ferns, but are neither. Cycads develop wood-like trunks with long fronds on trunk tips. Just like with conifers, cycads produce cones, but they arise from the trunk tip at the base of leaves. Many cycads are colloquially called palms by gardeners, and include the plant genera Cycas, Encephalartos, Zamia and Dioon, among a few others.
The only species still in existence today of this group of gymnosperms is the maidenhair tree (Ginkgo biloba). According to fossils, other species once existed eons ago. The maidenhair tree does exactly produce a seed like conifers or cycads, but an intermediate structure simply called an ovule. From an evolutionary standpoint, the ovule is an intermediate between the more primitive spore of ferns and the more advanced seed of other gymnosperms and angiosperms. The smelly, gooey "fruits" formed on ginkgo trees actually are ripe ovules, neither a true fruit nor a cone.
Scientists consider gymnosperm plants as precursors to angiosperms that are in wide existence today. The first gymnosperms appeared at the end of the Paleozoic Era in the Permian Period around 280 million years ago, according to the Palm and Cycad Societies of Florida's Geologic Timetable. Cycads and ginkgoes grew abundantly and widespread across the world. Across the Mesozoic Era, including the Jurassic and Triassic Periods, gymnosperms dominated landscapes and included conifer species. The first flowering plants appeared in the Jurassic Period and, alongside many gymnosperms, continue to exist today.
- Ohio State University; Gymnosperms; Michael Knee
- "A-Z Encyclopedia of Garden Plants"; Christopher Brickell and H. Marc Cathey, eds.; 2004
- Royal Botanic Gardens Sydney; Cycad History; Ken Hill
- Palm and Cycad Societies of Florida: Geologic Timetable
- Ginkgo Biloba: Reproduction
- Ginkgo Biloba: History