CH 22: Gymnosperms

In this chapter you will learn about  the differences between ferns and seed plants, and then briefly discuss the geological history of gymnosperms. The leaves, roots, and stems of pine trees are discussed, and pines are also used to portray the life cycle of a typical gymnosperm. Additional conifers, such as yews, podocarps, junipers, and redwoods are given brief mention, and a short discussion of other gymnosperms such as cycads, Ginkgo, Ephedra, Gnetum, and Welwitschia follows. The chapter concludes with a digest of the human and ecological relevance of gymnosperms, with particular emphasis on the conifers.

At the end of this chapter the successful student will be able to

• Describe the term Gymnosperm and the botany condition it represents. 
• Recognize the 4 major Phyla of Gymnosperms and their distinguishing characteristics
  • Phylum Pinophyta
  • Phylum Ginkgophyta
  • Phylum Cycadophyta
  • Phylum Gnetophyta
• Recognize the Human Relevance of Gymnosperms
  • Conifers
  • Other Gymnosperms
• Assignments
• Glossary

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Gymnosperm

• General characteristics of seed producing plants
  • Seed, a significant adaptation for land plants
  • Seed contains an embryo, protected in a seed coat
  • Pteridosperm or "seed ferns" were first seed producing plants
  • Two major groups of seed-bearing plants
    • a. Gymnosperms = naked seeds
    • b. Angiosperms = seeds contained in a fruit
• Gymnosperm refers to the exposed nature of the seeds.
  • Produced on the surface of sporophylls or similar structures instead of being enclosed within a fruit as in flowering plants.
    • Female gametophyte is produced inside an ovule that contains a nucellus.
      • Enclosed in integument.
  • Gymnosperms have cones or strobili; angiosperms have flowers
  • Gymnosperm sporophytes are trees or shrubs, with a few vine-like species
  • Gymnosperm gametophytes develop on the sporophyte
  • Gymnosperms have Four living Phyla
    • Phylum Pinophyta
    • Phylum Ginkgophyta
    • Phylum Cycadophyta
    • Phylum Gnetophyta

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Phylum Pinophyta-The Conifers

•  A. Pines
  • 1. General remarks
    • a. Largest genus is Pine (Pinus); more than 100 living species
    • b. Trees of the coniferous forests
    • c. Bristle-cone pines
      • 1) Oldest known living organisms
      • 2) Occur in White Mountains of California
  • 2. Structure and form
    • a. Leaves are needle-like (in clusters or bundles or 2 to 5)
      • 1) Adapted for harsh environments
        • a) hypodermis
        • b) thick cuticle
        • c) sunken stomata
        • d) no air space system in mesophyll
          • • conserves water with this arrangement
      • 2) Resin canals
        • • resin, prevents fungus growth and insect feeding
    • b. Wood is classified as softwood (versus hardwood of broadleaf trees)
      • 1) Absence of fibers
      • 2) Tracheids only, no vessels
      • 3) Annual rings
      • 
    • c. Bark may be extremely thick, insulates tree trunk against forest fires
      • • giant redwoods
    • d. Roots associated with fungus, called mycorrhizae
  • 3. Reproduction
    • a. Heterospory
    • b. Pollen cones (male) and seed cones (female)
    • c. Microsporangia and megasporangia
    • d. Microspores develop into pollen grains (male gametophytes)
    • e. Megaspores develop into female gametophytes
    • f. Ovule = nucellus (megasporangium) with an integument
    • 
      
      
• B. Other Conifers
  • 1. Yews
    • • seeds with fleshy, cup-like covering called an aril
  • 2. Podocarps
    • • planted as ornamentals
  • 3. Junipers
  • 4. Redwoods
    • a. Sequoia giganteum = Big Tree or Giant Redwood
      • • western slopes of California's Sierra Nevada mountains
    • b. Sequoia sempervirens = Coastal Redwood

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Phylum Ginkgophyta

• a. Structure and Form
  • 1) Trees with fan-shaped leaves
  • 2) Single species, Ginkgo biloba, called Maidenhair Tree or Silver Apricot
• b. Other Features
  • 1) Plant survives only because of cultivation
  • 2) Considered a living fossil
  • 3) Seeds resemble plums, have rank odor
• Ginkgo (Maidenhair Trees)
  • Only one living species
    • Notched, broad, fan-shaped leaves.
      • Leaves are produced in a spiral on short, slow-growing spurs.
        • No midrib or prominent veins.
      • Hair-like veins branch dichotomously.
    • Life cycle similar to pines.
      • Dioecious

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Phylum Cycadophyta

• a. Structure and Form
  • 1) Single unbranched stocky stem
  • 2) Palm or fern-like foliage
  • 3) Male and female cones on separate plants
  • 4) Slow growing plants
• b. Other Features
  • 1) Sub-tropical plants; Mexico, Cuba, Africa
  • 2) Considered living fossils
• The Cycads
  • Appearance of a cross between a tree fern and a palm.
    • Slow-growing plants of the tropics that have tall unbranched trunks.
      • Crown of largely pinnately divided leaves.
  • Life Cycle similar to conifers.
    • Pollination is generally brought about by beetles instead of wind.

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Phylum Gnetophyta

• a. Classification
  • 1) 70 species among only 3 genera
  • 2) Ephedra
    • a) Shrubby plants called joint firs
    • b) Inhabit drier regions of the world
  • 3) Gnetum
    • a) Vinelike plants with broad leaves
    • b) No English common name for this plant
    • c) Best known species is tree that grows up to 10 meters tall
  • 4) Welwitschia
    • a) Only one species
    • b) Confined to Namibian desert of southwestern Africa (Namibia)
    • c) Most unusual in appearance
    • d) Long taproot with two strap-like leaves
    • e) Obtains its water from fog
• b. Other Features
  • • vessels in the xylem, all other gymnosperms have tracheids

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Human and Ecological Relevance of Conifers

•  1. Pine trees—"many parts are edible"
  • • bark and seeds
• 2. Masts of sailing vessels (eastern white pine)
• 3. Turpentine and rosin
  • • naval stores, caulking and sealing wooden sailing ships
• 4. Amber
  • • fossilized resins with entrapped insects
• 5. Pulpwood
  • • major source is white spruce
• 6. Soundboards of musical instruments (violins, etc.)
• 7. Douglas fir
  • • lumber
• 8. Arborvitae
  • • ornamentals
• 9. Juniper berries
  • • used to flavor gin
• 10. Pacific yew
  • • taxol, a drug with anticancer properties, obtained from bark
• 11.  Conifers are used for Crates, Boxes, Matchsticks, Furniture, and Telephone poles

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Human and Ecological Relevance or Other Gymnosperms

• 1. Arrowroot starch (from cycads)
• 2. Ginkgo
  • a. Seeds edible
  • b. Leaf extracts improve blood supply to brain and lungs
• 3. Mormon tea
  • • from Ephedra leaves
• 4. Ephedrine drug
  • • from Chinese Ephedra
• 5. Gnetum rope (used in Java)
  • • from bark fibers

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Last modified: October 08, 2004 by Cynthia Herbrandson  © Copyright 1999, Kellogg Community College. All rights reserved.