Gymnosperm

Gymnosperms are a special group of plants that make seeds, but unlike most plants you might know, their seeds aren't wrapped in a protective covering. Instead, these seeds grow on the surface of scales or leaves, often forming cones. This group includes conifers like pines and firs, cycads, ginkgo, and gnetophytes. The name "gymnosperm" comes from ancient words meaning "naked seed," which describes how their seeds are uncovered.

These plants have a unique life cycle that includes both diploid and haploid stages, with the diploid stage being more prominent. Gymnosperms and flowering plants together make up the seed plants, which are divided into several groups. Today, the largest group of gymnosperms are the conifers, followed by cycads, gnetophytes, and the single surviving species of ginkgo.

Many gymnosperms have special relationships with fungi or bacteria. For example, some conifers like pines have fungal associations with their roots, while others like cycas have tiny roots that work with bacteria to fix nitrogen. These relationships help the plants grow better in different environments.

Diversity and origin

Over 1,000 different kinds of gymnosperms are alive today. Scientists used to think these plants began growing in a time called the Late Carboniferous. But newer studies show they started growing even earlier, in the Early Carboniferous. These plants spread out and changed a lot during the Late Carboniferous, possibly because of a big change in their genes about 319 million years ago. Early signs of these plants can be seen in fossils from the Devonian period, around 383 million years ago.

All gymnosperms are plants that live for many years and have wood. Unlike other gymnosperms, cycads have softer wood and get support from tough parts at the base of their leaves. Gymnosperms include special kinds of plants like parasites, plants that grow on other plants, and plants that grow in flowing water.

Conifers are the most common gymnosperms, with about 600 to 630 different types. Most conifers keep their leaves all year and make their seeds inside special protective cones called strobili. Usually, both male and female cones grow on the same conifer tree, and they are pollinated by the wind.

Cycads are smaller, palm-like trees and are most common in tropical areas near the equator. There are also about 95 to 100 types of gnetophytes and one type of ginkgo, which has tall trees with special two-lobed leaves. Gnetophytes include plants and shrubs, like the unusual Welwitschia that grows horizontally.

Gymnosperms are currently the most at-risk group of plants.

Evolution

Phylogeny

Further information: Spermatophyte

Scientists have studied how gymnosperms developed and changed over time.

Taxonomy

Gymnosperms are a special group of plants that make up a single family within the larger group of spermatophytes. They include both living and ancient plants. Some old gymnosperms look a bit like ferns but have seeds. There are about 12 families and over 1,000 different types of living gymnosperms today.

Subclass Cycadidae

• Order Cycadales
  • Family Cycadaceae: Cycas
  • Family Zamiaceae: Dioon, Bowenia, Macrozamia, Lepidozamia, Encephalartos, Stangeria, Ceratozamia, Microcycas, Zamia

Subclass Ginkgoidae

• Order Ginkgoales
  • Family Ginkgoaceae: Ginkgo

Subclass Gnetidae

• Order Welwitschiales
  • Family Welwitschiaceae: Welwitschia
• Order Gnetales
  • Family Gnetaceae: Gnetum
• Order Ephedrales
  • Family Ephedraceae: Ephedra

Subclass Pinidae

• Order Pinales
  • Family Pinaceae: Cedrus, Pinus, Cathaya, Picea, Pseudotsuga, Larix, Pseudolarix, Tsuga, Nothotsuga, Keteleeria, Abies
• Order Araucariales
  • Family Araucariaceae: Araucaria, Wollemia, Agathis
  • Family Podocarpaceae: Phyllocladus, Lepidothamnus, Prumnopitys, Sundacarpus, Halocarpus, Parasitaxus, Lagarostrobos, Manoao, Saxegothaea, Microcachrys, Pherosphaera, Acmopyle, Dacrycarpus, Dacrydium, Falcatifolium, Retrophyllum, Nageia, Afrocarpus, Podocarpus
• Order Cupressales
  • Family Sciadopityaceae: Sciadopitys
  • Family Cupressaceae: Cunninghamia, Taiwania, Athrotaxis, Metasequoia, Sequoia, Sequoiadendron, Cryptomeria, Glyptostrobus, Taxodium, Papuacedrus, Austrocedrus, Libocedrus, Pilgerodendron, Widdringtonia, Diselma, Fitzroya, Callitris, Actinostrobus, Neocallitropsis, Thujopsis, Thuja, Fokienia, Chamaecyparis, Cupressus, Juniperus, Calocedrus, Tetraclinis, Platycladus, Microbiota
  • Family Taxaceae: Austrotaxus, Pseudotaxus, Taxus, Cephalotaxus, Amentotaxus, Torreya

Extinct groupings

• Order Cordaitales
• Order Calamopityales
• Order Callistophytales
• Order Caytoniales
• Order Gigantopteridales
• Order Glossopteridales
• Order Lyginopteridales
• Order Medullosales
• Order Peltaspermales
• Order Corystospermales (also known as Umkomasiales)
• Order Czekanowskiales
• Order Bennettitales (cycadeoids)
• Order Erdtmanithecales
• Order Pentoxylales
• Order Petriellales

Life cycle

Gymnosperms, like all vascular plants, spend most of their life with cells that have two sets of chromosomes. Their phase for making gametes (cells that combine to create a new plant) is short. They produce two kinds of spores: small ones called microspores from microsporangium and larger ones called megaspores from megasporangium. These spores are found in special cones on the plant.

When pollen moves from one plant to another, it reaches the ovule. Inside the ovule, the pollen grows and makes sperm cells. The sperm meets the egg, and this creates a new embryo inside the seed. The seed also contains food from the parent plant to help the embryo grow.

Genetics

In 2013, scientists completed the first full DNA map, or genome, for a gymnosperm. The plant they studied was Picea abies, a type of spruce tree. This helped researchers learn more about these special plants and their genes.

Uses

Gymnosperms are very useful for people. Trees like pine, fir, spruce, and cedar are used to make lumber, paper, and resin. Other gymnosperms are used to make soap, varnish, nail polish, food, gum, and perfumes.