1 / 26

Introduction to Seed Plants: Gymnosperms

Introduction to Seed Plants: Gymnosperms . Chapter 22. Outline. Introduction Phylum Pinophyta – The Conifers Other Gymnosperms Phylum Ginkgophyta – Ginkgo Phylum Cycadophyta – The Cycads Phylum Gnetophyta – The Gnetophytes Human Relevance of Gymnosperms Conifers

solana
Download Presentation

Introduction to Seed Plants: Gymnosperms

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Introduction to Seed Plants: Gymnosperms Chapter 22

  2. Outline • Introduction • Phylum Pinophyta – The Conifers • Other Gymnosperms • Phylum Ginkgophyta – Ginkgo • Phylum Cycadophyta – The Cycads • Phylum Gnetophyta – The Gnetophytes • Human Relevance of Gymnosperms • Conifers • Other Gymnosperms

  3. Introduction • Oldest known seeds - Late Devonian, >350 mya • Seeds = significant adaptation for plants on land • Protective seed coat • Supply of food for embryo • Capable of dormancy in unfavorable environmental conditions • 1stseed plants fernlike in appearance = pteridosperms (seed ferns) - reclassified as gymnosperms

  4. Introduction • Gymnosperm refers to exposed nature of seeds • Seeds produced on surface of sporophylls or similar structures, instead of enclosed within fruit as in flowering plants • Seed-bearing and pollen-bearing sporophylls often arranged in cones

  5. Introduction • Pollen cones produce pollen grains • Female gametophyte - produced inside ovule containing nucellus • Nucellus enclosed in integument • Integument becomes seed coat after fertilization • Female gametophyte more reduced in cell # than ferns and their relatives • Does not grow independently, but develops within sporophytestructures

  6. Introduction • 4 living phyla • Pinophyta - pines, firs, spruces, cedars • Fossils date back to late Carboniferous, 290mya • Ginkgophyta - single living representative, Ginkgo • Tree with fan-shaped leaves • Seeds enclosed in fleshy covering • Cycadophyta -leaves superficially palm-like • Gnetophyta -3 genera • Wood with vessels

  7. Phylum Pinophyta – The Conifers • Pines (Pinus) • Dominant trees in coniferous forests of Northern Hemisphere • Include world’s oldest known living organisms - Bristlecone pines • Structure and form: • Leaves needlelike and arranged in clusters of 2-5 leaves • Cluster = fascicle • Fascicles = short shootswith restricted growth

  8. Phylum Pinophyta – The Conifers • Structure and form cont’d.: • Modifications to survive harsh conditions • Hypodermis located below epidermis • 1-2 layers of thick-walled cells • Thick cuticle • Recessed or sunken stomata • Resin canals • Resin antiseptic and aromatic, prevents development of fungi, and deters insects • Mycorrhizal fungi associated with roots of most conifers

  9. Phylum Pinophyta – The Conifers • Structure and form cont’d.: • Wood consists entirely of tracheids • Conifer wood = softwood - thick-walled cells absent • Dicot wood = hardwood - thick-walled vessels and fibers present

  10. Phylum Pinophyta – The Conifers • Reproduction: • 2 kinds of spores • Pollen cones (male strobili) - papery or membranous scales • Microsporangia in pairs toward bases of scales

  11. Phylum Pinophyta – The Conifers • Reproduction cont’d.: • Microspores develop into pollen grains • Pollen grain consists of 4 cells and pair of air sacs aiding in wind dispersal

  12. Phylum Pinophyta – The Conifers • Reproduction cont’d.: • Megaspores in megasporangia within ovules • Pair of ovules at bases of seed cone scales • Seed cones larger than pollen cones • Have woody scales with inconspicuous bracts between

  13. Phylum Pinophyta – The Conifers • Reproduction cont’d.: • Ovule containsmegasporangiumcontainingnucellusand single megasporocyte • Megasporangium surrounded by integument • Integument has pore = micropyle • Megasporocyte undergoes meiosis, producing 4 megaspores • 3 megaspores degenerate • Remaining megaspore develops into female gametophyte with archegonia at micropyleend

  14. Phylum Pinophyta – The Conifers • Reproduction cont’d.: • Seed cones take 2 years to mature • 1st year: • Pollen grains catch on sticky pollen drops oozing out of micropyle • Pollen grain produces pollen tube that grows through nucellus • 2 sperms produced in pollen tube • Mature male gametophyte = germinated pollen grain with pollen tube and 2 sperm • Sperm have no flagella and no antheridium • Megaspore develops

  15. Phylum Pinophyta – The Conifers • Reproduction cont’d.: • 2nd year: • Female gametophyte and archegoniummature • Pollen tube arrives at archegonium • 1 sperm unites with egg, forming zygote • Other sperm degenerates • Embryo nourished by female gametophyte • Integument becomes seed coat

  16. Phylum Pinophyta – The Conifers

  17. Phylum Pinophyta – The Conifers • Other Conifers: • Yew (Taxus) and California nutmeg (Torreya) produce ovules singly at tips of shoots • Each ovule at least partially surrounded by fleshy, cuplike aril • Southern hemisphere conifer - Podocarpus • Fleshy-coated seeds with large appendage at base • Junipers - seed cones fleshy Taxus Podocarpus

  18. Other Gymnosperms • Phylum Ginkgophyta – Ginkgo (maidenhair trees) • 1 living species only existing in cultivation • Notched, broad, fan-shaped leaves • Leaves on short, slow-growing spurs • No midrib or prominent veins • Hair-like veins branch dichotomously • Deciduous

  19. Other Gymnosperms • Life cycle similar to pines • Dioecious - male and female structures on separate trees • Seeds enclosed in fleshy seed coat with nauseating odor Seeds and leaves Male strobili

  20. Other Gymnosperms • Phylum Cycadophyta – The Cycads • Slow-growing plants of tropics and subtropics • Tall unbranched trunks • Crown of large pinnately divided leaves • Life cycle similar to conifers • Pollination sometimes by beetles • Dioecious • Has pollen and seed strobili Male cycad Female cycad

  21. Other Gymnosperms Part of plant • Phylum Gnetophyta – The Gnetophytes • Unique among gymnosperms in having vessels in xylem • Joint firs (Ephedra) - shrubby plants of drier regions of southwestern North America Male strobili Female strobilus Ephedra

  22. Other Gymnosperms • Phylum Gnetophyta – The Gnetophytes • Gnetum - vine-like plants with broad leaves • In tropics

  23. Other Gymnosperms • Phylum Gnetophyta – The Gnetophytes • Welwitschia - only 1 species, confined to deserts of southwestern Africa • Short stem • Long taproot • Only 2 straplike leaves that become tattered and split • Dioecious • Has male and female strobili

  24. Human Relevance of Gymnosperms • Conifers • Edible inner bark and needles of white pine, and seeds of nearly all pines • Masts in sailing vessels • Crates, boxes, matchsticks, furniture • Telephone poles, railroad ties, mine timbers • Turpentine and rosin (both from resin) • Fuel • Pulpwood • Construction lumber • Ornamentals • Pharmaceuticals (taxol for ovarian cancer from yew trees)

  25. Human Relevance of Gymnosperms • Other Gymnosperms • Ginkgo: • Seeds for food (after seed coat removal) • Ginkgo extracts to increase blood circulation • Ephedra - Mormon tea • Drug ephedrine for respiratory problems from Chinese species

  26. Review • Introduction • Phylum Pinophyta – The Conifers • Other Gymnosperms • Phylum Ginkgophyta – Ginkgo • Phylum Cycadophyta – The Cycads • Phylum Gnetophyta – The Gnetophytes • Human Relevance of Gymnosperms • Conifers • Other Gymnosperms

More Related