Introduction to Seed Plants: Gymnosperms Chapter 22 Lecture Outline Introduction to Seed Plants: Gymnosperms Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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

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

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

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.

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

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

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.

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.

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.

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.

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

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.

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.

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.

Phylum Pinophyta – The Conifers Pines - Reproduction:

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

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

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

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

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

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

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

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)

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

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