BSCI 124 Lecture Notes

Undergraduate Program in Plant Biology, University of Maryland


I. Introduction [For a detailed review of the Plant Kingdom, see the site maintained by Cardillo & Samuels; see also an historical review of the kingdoms and an overall view of them.]

  1. Gymnosperms [REQUIRED READING] (Pinophyta; sometimes called Coniferophyta or less commonly Gymnospermae), plants with seeds that are not enclosed within a fruit, derive their name from the Greek words gymnos (naked) and sperma (seed). In this plant group, the seeds are produced on the open surface of a scale. Unlike flowering plants, the gymnosperms do not form true flowers or fruits.
  2. Examples of gymnosperms include cycads, ginkgo, conifers and gnetops.

II. Evolution

  1. Evolved from fern-like ancestors.
  2. Evolutionary advancements over the ferns:
    1. Seeds.
    2. Lack of dependence on water for fertilization (air-borne pollen).
    3. Progressively more dominant sporophyte.
    4. Heterospory.
    5. Life Cycle
      1. In the gymnosperms and the flowering plants, the sporophyte generation is dominant with the gametophyte contained in and dependent on the sporophyte.
    6. Vascular system - check out this important review site!
      1. They do have a well-developed vascular system of xylem and phloem and have true roots, stems, and leaves.
      2. The vascular tissues are significantly more efficient and effective than the vascular systems of the seedless plants such as the ferns.
      3. Gymnosperms are usually woody plants. The xylem form the wood if a tree and the phloem tissues are part of the bark (along with cork). The formation of wood from secondary growth is the reason that some sporophytes can reach such large sizes.


  1. Primary versus secondary growth; what secondary growth accomplishes
    1. Primary growth is growth originating in the apical meristems of the shoots and roots - results in an increase in length.
    2. Secondary growth is growth derived from secondary or lateral meristems - results in an increase in girth; example of secondary growth- trees (wood and bark)
      1. Results from the activity of two lateral meristems
      2. Vascular cambium- forms secondary xylem (essentially all tracheids in gymnosperms; tracheids and vessels in angiosperms) and secondary phloem
  2. Wood = secondary xylem (conducts water & dissolved minerals); many of these cells are dead at maturity=> only the cell walls remain
    1. Inner bark = secondary phloem (conducts food)
    2. Cork cambium- forms cork cells and cork parenchyma (provides protection)
    3. Outer bark = cork and cork parenchyma Anatomy of a young woody stemwoody stem
    4. Annual rings
      1. Spring wood- vessel diameter large, walls thinner
      2. Late summer wood- vessel diameter small, walls thicker -- as seen here
      3. Tropical trees- no annual rings since the seasons are not so different from each other
      4. Dendrochronology - detecting climatic and archaeological changes by tree ring analysis
  3. Most important group of gymnosperms- conifers
    1. The largest and most familiar group of gymnosperms living today are the conifers, which almost always bear their seeds in cones.
      1. Staminate cones are the male cones and the ovulate cones are female.
      2. See male and female cones of Pinus flexilis (limber pine), and immature and mature female cones of Pseudotsuga menziesii var. glauca (inland Douglas fir)
    2. They are mainly woody plants
    3. Include:
      1. the oldest living trees (bristlecone pines in eastern Nevada, 4950 years old (now cut down)),
      2. the most massive trees (Sequoiadendron giganteum, giant sequoia: up to 375 feet tall and 41 feet across),
      3. the tallest living trees (Sequoia sempervirens, a redwood) at 367.5 feet tall; in 1872 a specimen of Eucalyptus regnans from Australia were measured by William Ferguson, a surveyor, to be around 435 feet tall; others estimated individual trees to have been as much as 521 ft but such reports are generally discounted
    4. While at least some representatives are found worldwide, conifers are mostly trees of temperate to extremely cold regions. Conifers demonstrate remarkable adaptations to harsh climates where little liquid water is available for much of the year. For example, most conifers have tough, narrow leaves called needles that are adapted in several ways to conserve water. Conifers also have resins which act to protect the plant from predation.
  4. Significance of gymnosperms
    1. Ecological importance
      1. Provide food (especially seeds) and cover/habitat for wildlife
      2. Great forests prevent soil erosion
      3. Reduce greenhouse gasses
  5. Commercial importance
    1. Lumber/paper industry- fence posts, musical instruments, pencils, cedar chests, lawn furniture, cardboard, paper
    2. Resins and turpentine
    3. Ornamental plants, Christmas trees
    4. Food- pine nuts (pine seeds)
    5. "Felling the Giants" by Stephen Michael Payne: A history of the redwood forest in central California.
  6. Living fossils [REQUIRED READING]

IV. FOR YOUR INFORMATION ONLY: Major groups of gymnosperms (Division Pinophyta)

  1. Subdivision Cycadophytina (cycads; often incorrectly called "Cycadicae")
    1. Features
      a. Life history and ecology
      b. Cycads: Extant and extinct
      c. All about cycads
      d. Cycads and dinosaurs
  2. Subdivision Ginkgoophytina (ginkgo; often incorrectly called "Ginkgoatae")
    1. Features
      a. Ginkgo State Park: Lots of information of ginkgo
      b. History of Ginkgo and its medicinal value - a "hot" medical plant newly rediscovered in the Western World
      c. Cultivated ginkgo
  3. Subdivision Pinophytina (conifers: often incorrectly called "Pinatae")
  4. Subdivision Gnetophytina (gnetops: often incorrectly called "Gneticae")
    1. Features
    2. Examples:
      1. Ephedra: Mormon tea, a medicinal plant - an ancient medicinal plant [sorry for the commercial]
      2. Gnetum
      3. Welwitschia: world's most bizarre plant, found only on the Namib Desert -- the world's oldest desert
  5. Other names for the gymnosperms
    1. Some consider each of the above subdivisions (or subphyla) to be distinct divisions (or phyla), namely:
      1. Cycadophyta
    2. Some consider all seed plants to form a division and call it Spermatophyta or as a class Spermatopsida
      1. Plants with vascular tissue are sometimes called Tracheophyta or informally "tracheophytes"
      2. Informally, the bryophytes and the seed plants may collectively be termed "embryophytes"
    3. Fossil gymnosperms
    4. seed ferns (progymnosperms)

Other Sites of Interest:
Outline Review
Brief review
All about the naked seeds of gymnosperms
Secondary Growth: A review with access to good illustrations
Old Growth Forests
All about bristlecone pines
Information on giant sequoia
Conifer images
Botanical records from Wayne's World
* World's oldest living thing
* World's oldest living fossil
* World's most massive living things
* World's tallest tree
* World's hardest and heaviest wood
Information on Tree Rings
Trees older than Methuselah by Bryan Ness
Web links for the gymnosperms
Web links for Pinophyta
Major families of Pinophyta
Ginkgo biloba-web site of diverse subjects on the tree
Cycads for the garden
The Dinosauria

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Last revised: 23 Aug 1998 - Reveal