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By far the largest group of living gymnosperms are the conifers (pines, cypresses, and relatives), followed by cycads, gnetophytes (Gnetum, Ephedra and Welwitschia), and Ginkgo biloba (a single living species). About 65% of gymnosperms are dioecious, [5] but conifers are almost all monoecious. [6]
Oct 26, 2024 · Examples of Gymnosperms. There are many familiar gymnosperms, including: Pine (Pinus): A common conifer found in temperate forests. Cypress (Cupressus): Known for its aromatic wood and evergreen nature. Ginkgo (Ginkgo biloba): The only surviving member of an ancient lineage, recognized by its fan-shaped leaves.
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- General features
gymnosperm, any vascular plant that reproduces by means of an exposed seed, or ovule—unlike angiosperms, or flowering plants, whose seeds are enclosed by mature ovaries, or fruits. The seeds of many gymnosperms (literally, “naked seeds”) are borne in cones and are not visible until maturity. Taxonomists recognize four distinct divisions of extant (nonextinct) gymnospermous plants—Pinophyta, Cycadophyta, Ginkgophyta, and Gnetophyta—with 88 genera and more than 1,000 species distributed throughout the world.
Gymnosperms were dominant in the Mesozoic Era (about 252.2 million to 66 million years ago), during which time some of the modern families originated (Pinaceae, Araucariaceae, Cupressaceae). Although since the Cretaceous Period (about 145 million to 66 million years ago) gymnosperms have been gradually displaced by the more recently evolved angiosperms, they are still successful in many parts of the world and occupy large areas of Earth’s surface. Conifer forests, for example, cover vast regions of northern temperate lands, and gymnosperms frequently grow in more northerly latitudes than do angiosperms.
In all living gymnosperm groups, the visible part of the plant body (i.e., the growing stem and branches) represents the sporophyte, or asexual, generation, rather than the gametophyte, or sexual, generation. Typically, a sporophyte has a stem with roots and leaves and bears the reproductive structures. As vascular plants, gymnosperms contain two conducting tissues, the xylem and phloem. The xylem conducts water and minerals from the roots to the rest of the plant and also provides structural support. The phloem distributes the sugars, amino acids, and organic nutrients manufactured in the leaves to the nonphotosynthetic tissues of the plant.
In most gymnosperms the male pollen cones, called microstrobili, contain reduced leaves called microsporophylls. Microsporangia, or pollen sacs, are borne on the lower surfaces of the microsporophylls. The number of microsporangia may vary from two in many conifers to hundreds in some cycads. Within the microsporangia are cells which undergo meiotic division to produce haploid microspores.
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The gametophyte phase begins when the microspore, while still within the microsporangium, begins to germinate to form the male gametophyte. A single microspore nucleus divides by mitosis to produce a few cells. At this stage the male gametophyte (called a pollen grain) is shed and transported by wind or insects.
Female ovulate cones, called megastrobili, may be borne on the same plant that bears microstrobili (as in conifers) or on separate plants (as in cycads and Ginkgo). A megastrobilus contains many scales, called megasporophylls, that contain megasporangia. Within each megasporangium, a single cell undergoes meiotic division to produce four haploid megaspores, three of which typically degenerate. The remaining megaspore undergoes mitosis to form the female gametophyte. As the number of free nuclei multiplies, the megasporangium and megaspore wall expand. At this stage the ovule is ready to be fertilized.
May 2, 2018 · Today, there over one thousand species of gymnosperms belonging to four main divisions: Coniferophyta, Cycadophyta, Ginkgophyta, and Gnetophyta. Coniferophyta Gymnosperms: Cycad Cones.
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Apr 27, 2017 · The gymnosperms consist of the conifers, the cycads, the gnetophytes and the sole extant species of the Gynkgophyta division, the Gingko biloba. Examples of Gymnosperm. Conifers, in the division Pinophyta or Coniferophyta, are the most numerous of the gymnosperms; woody and with vascular tissue, these are cone bearing trees and shrubs.
Sep 13, 2024 · The term gymnosperm (“naked seeds”) represents four extant divisions of vascular plants whose ovules (seeds) are exposed on the surface of cone scales. The cone-bearing gymnosperms are among the largest and oldest living organisms in the world. They dominated the landscape about 200 million years ago.
Gymnosperms are heterosporous seed plants that produce naked seeds. They appeared in the Paleozoic period and were the dominant plant life during the Mesozoic. Modern-day gymnosperms belong to four phyla.
