Introduction to Seed Plants: Gymnosperms

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