1. Introduction to Seed Plants: Gymnosperms
Chapter 22
Lecture Outline
Introduction to Seed Plants: Gymnosperms
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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

3. Introduction
Seeds provide a significant adaptation for plants on land.
Advantages:
First seed plants fernlike in appearance = pteridosperms (seed ferns) - Reclassified as gymnosperms

4. Introduction Gymnosperm =
Seeds produced on surface of sporophylls or similar structures
Large Reproductive Structure: Seed- bearing and pollen- bearing sporophylls often arranged in ___________.

5. Introduction Male Cones = Pollen cones produce:
Female Cones: contain ovules that becomes the seeds
Reproductive Tissue: Each ovule contains the Female Sporangium (Nucellus) enclosed in integument.
Integument becomes seed coat of seed.
Female Gametophyte: is produced by female sporangium within cone and remains in cone.
Size: even more reduced in cell number than are ferns and their relatives.
Does not grow independently, but develops within sporophyte structures and eventually produces egg.

6. Introduction Four living phyla
Pinophyta - Pines, firs, spruces, cedars
Fossils date back to late Carboniferous, 290 million years ago.
Ginkgophyta - Has single living representative, Ginkgo
Tree with fan-shaped leaves
Seeds enclosed in fleshy covering.
Cycadophyta - Leaves superficially palmlike.
Gnetophyta - Three 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 two to five leaves.
Cluster = fascicle
Fascicles = short shoots - Have restricted growth

8. Phylum Pinophyta – The Conifers
Pines - Structure and form:
Have modifications that enable them to survive harsh conditions
Hypodermis located below the epidermis.
One to two layers of thick-walled cells
Thick cuticle
Recessed or sunken stomata
Resin canals
Resin is antiseptic and aromatic, prevents development of fungi, and deters insects.
Mycorrhizal fungi associated with roots of most conifers.

9. Phylum Pinophyta – The Conifers
Pines - Structure and form:
Wood consists entirely of tracheids.
Conifer wood = softwood - Thick-walled cells absent.
Broadleaf tree (dicot) wood = hardwood - Thick-walled vessels and fibers present.

10. Phylum Pinophyta – The Conifers
Pines
Reproduction:
Two kinds of spores produced.
Pollen cones (male strobili) consist of papery or membranous scales.
Microsporangia in pairs toward bases of scales.

11. Phylum Pinophyta – The Conifers
Pines
Reproduction:
Meiosis produces microspores that then develop into pollen grains.
Pollen grain consists of four cells and a pair of air sacs.
Air sacs add buoyancy in wind.

12. Phylum Pinophyta – The Conifers
Pines
Reproduction:
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
Pines - Reproduction:
Ovule contains a megasporangium containing a megasporangium and a single megasporocyte.
Megasporangium surrounded by integument.
Integument has a pore called micropyle.
Megasporocyte undergoes meiosis, producing four megaspores.
Three megaspores degenerate.
Remaining megaspore develops into female gametophyte with archegonia at micropyle end.

14. Phylum Pinophyta – The Conifers
Pines - Reproduction:
Seed cones take two years to mature.
First year:
Pollen grains catch on sticky pollen drops oozing out of micropyle.
Pollen grain produces pollen tube that grows through microphyle.
Two sperms produced in pollen tube.
Mature male gametophyte = germinated pollen grain with pollen tube and two sperm
Sperm have no flagella and no antheridium is formed.
Megaspore develops.

15. Phylum Pinophyta – The Conifers
Pines - Reproduction:
Second year:
Female gametophyte and archegonium mature.
Pollen tube arrives at archegonium.
One sperm unites with egg, forming zygote.
Other sperm degenerates.
Embryo nourished by female gametophyte.
Integument becomes seed coat.

16. Phylum Pinophyta – The Conifers
Pines - Reproduction:

19. 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

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

21. Other Gymnosperms Phylum Ginkgophyta 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

22. 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

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

24. Other Gymnosperms Phylum Gnetophyta – The Gnetophytes
Gnetum - Vine-like plants with broad leaves
In tropics

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

26. 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)

27. 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 a Chinese species

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