World Library  
Flag as Inappropriate
Email this Article

Gymnosperms

Article Id: WHEBN0000745055
Reproduction Date:

Title: Gymnosperms  
Author: World Heritage Encyclopedia
Language: English
Subject: Chloroplast, Pinophyta, Chlamydomonas, Archegonium, Mandla Plant Fossils National Park, Microsporangia, Karoo Ice Age, August W. Eichler, Woody plants of Soldiers Delight, Robert Harold Compton
Collection:
Publisher: World Heritage Encyclopedia
Publication
Date:
 

Gymnosperms

Gymnosperm
Temporal range: 370–0Ma
Devonian - Recent
Conifers, including the pines and related trees and shrubs, are a major division of gymnosperms.
Scientific classification
Kingdom: Plantae
Subkingdom: Embryophyta
(unranked): Gymnospermae (paraphyletic)
Divisions

Pinophyta (or Coniferophyta) - Conifers
Ginkgophyta - Ginkgo
Cycadophyta - Cycads
Gnetophyta - Gnetum, Ephedra, Welwitschia

The gymnosperms are a group of seed-producing plants that includes conifers, cycads, Ginkgo, and Gnetales. The term "gymnosperm" comes from the Greek word gymnospermos (γυμνόσπερμος), meaning "naked seeds", after the unenclosed condition of their seeds (called ovules in their unfertilized state). Their naked condition stands in contrast to the seeds and ovules of flowering plants (angiosperms), which are enclosed within an ovary. Gymnosperm seeds develop either on the surface of scales or leaves, often modified to form cones, or at the end of short stalks as in Ginkgo.

The gymnosperms and angiosperms together compose the spermatophytes or seed plants. By far the largest group of living gymnosperms is the conifers (pines, cypresses, and relatives), followed by cycads, Gnetophytes (Gnetum, Ephedra and Welwitschia), and Ginkgo (a single living species).

Classification

Further information: Spermatophyte

In early classification schemes, the gymnosperms (Gymnospermae) were regarded as a "natural" group. There is conflicting evidence on the question of whether the living gymnosperms form a clade.[1][2] The fossil record of gymnosperms includes many distinctive taxa that do not belong to the four modern groups, including seed-bearing trees that have a somewhat fern-like vegetative morphology (the so-called "seed ferns" or pteridosperms.)[3] When fossil gymnosperms such as Bennettitales, Caytonia and the glossopterids are considered, it is clear that angiosperms are nested within a larger gymnosperm clade, although which group of gymnosperms is their closest relative remains unclear.

For the most recent classification on extant gymnosperms see Christenhusz et al. (2011).[4]

Subclass Cycadidae

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

Subclass Ginkgoidae

Subclass Gnetidae

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 (incl. Actinostrobus), Neocallitropsis, Thujopsis, Thuja, Fokienia, Chamaecyparis, Cupressus, Juniperus, Calocedrus, Tetraclinis, Platycladus, Microbiota
    • Family Taxaceae: Austrotaxus, Pseudotaxus, Taxus, Cephalotaxus, Amentotaxus, Torreya

Diversity and origin

There are more than 1000[5] extant or currently living species of Gymnosperms in 88[5] plant genera belonging to 14 plant families.

It is widely accepted that the gymnosperms originated in the late

Conifers are by far the most abundant extant group of gymnosperms with six to eight families, with a total of 65-70 genera and 600-630 species (696 accepted names).[10] Conifers are woody plants and most are evergreens.[11] The leaves of many conifers are long, thin and needle-like, others species, including most Cupressaceae and some Podocarpaceae, have flat, triangular scale-like leaves. Agathis in Araucariaceae and Nageia in Podocarpaceae have broad, flat strap-shaped leaves.

Cycads are the next most abundant group of gymnosperms, with two or three families, 11 genera, and approximately 300 species. The other extant groups are the 75-80 species of Gnetales and one species of Ginkgo.

Uses

Gymnosperms have major economic uses. Pine, fir, spruce, and cedar are all examples of conifers that are used for lumber. Some other common uses for gymnosperms are soap, varnish, nail polish, food, gum, and perfumes.

Life cycle

Gymnosperms, like all vascular plants have a sporophyte-dominant life-cycle. The gametophyte (gamete-bearing phase) is relatively short-lived. Two spore types, microspores and megaspores, are typically produced in pollen cones or ovulate cones, respectively. Gametophytes, as with all heterosporous plants, develop within the spore wall. Pollen grains (microgametophytes) mature from microspores, and ultimately produce sperm cells. Megagametophytes develop from megaspores and are retained within the ovule. They typically produce multiple archegonia. During pollination, pollen grains are physically transferred between plants, from pollen cone to the ovule, being transferred by wind or insects. Whole grains enter each ovule through a microscopic gap in the ovule coat (integument) called the micropyle. The pollen grains mature further inside the ovule and produce sperm cells. Two main modes of fertilization are found in gymnosperms. Cycads and Ginkgo have motile sperm that swim directly to the egg inside the ovule, whereas conifers and gnetophytes have sperm with no flagella that are conveyed to the egg along a pollen tube. After fertilization (joining of the sperm and egg cell), the zygote develops into an embryo (young sporophyte). More than one embryo is usually initiated in each gymnosperm seed. The mature seed comprises the embryo and the remains of the female gametophyte, which serves as a food supply, and the seed coat (integument).[12]

Genetics

The first sequenced genome for any gymnosperm was the genome of Picea abies in 2013.[13]

References

External links

  • Gymnosperm Database
  • Gymnosperms on the Tree of Life


Template:Nuts

This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.
 



Copyright © World Library Foundation. All rights reserved. eBooks from World eBook Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.