introduction to seed plants: gymnosperms
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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 - PowerPoint PPT PresentationTRANSCRIPT
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• Other Gymnosperms
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
1st seed plants fernlike in appearance = pteridosperms (seed ferns) - reclassified as gymnosperms
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
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
sporophyte structures
Introduction 4 living phyla• Pinophyta - pines, firs, spruces, cedars−Fossils date back to late Carboniferous, 290
mya• 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
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 shoots with
restricted growth
Phylum Pinophyta – The Conifers• Structure and form cont’d.:
−Modifications to survive harsh conditionsHypodermis located below epidermis»1-2 layers of thick-walled cells
Thick cuticleRecessed or sunken stomataResin canals»Resin antiseptic and aromatic, prevents
development of fungi, and deters insectsMycorrhizal fungi associated with roots of most
conifers
Phylum Pinophyta – The Conifers• Structure and form cont’d.:– Wood consists entirely of tracheids
Conifer wood = softwood - thick-walled cells absentDicot wood = hardwood - thick-walled vessels and
fibers present
Phylum Pinophyta – The Conifers• Reproduction:
−2 kinds of spores
−Pollen cones (male strobili) - papery or membranous scalesMicrosporangia
in pairs toward bases of scales
Phylum Pinophyta – The Conifers• Reproduction cont’d.:
−Microspores develop into pollen grainsPollen grain
consists of 4 cells and pair of air sacs aiding in wind dispersal
Phylum Pinophyta – The Conifers• Reproduction cont’d.:
−Megaspores in megasporangia within ovulesPair of ovules at
bases of seed cone scales
−Seed cones larger than pollen conesHave woody scales
with inconspicuous bracts between
Phylum Pinophyta – The Conifers• Reproduction cont’d.:– Ovule contains
megasporangium containing nucellus and 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 micropyle end
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
Phylum Pinophyta – The Conifers• Reproduction cont’d.:−2nd year:
Female gametophyte and archegonium mature
Pollen tube arrives at archegonium1 sperm unites with egg, forming zygote»Other sperm degenerates
−Embryo nourished by female gametophyte−Integument becomes seed coat
Phylum Pinophyta – The Conifers
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)• 1 living species only existing in
cultivation• Notched, broad, fan-shaped
leaves−Leaves on short, slow-
growing spursNo midrib or prominent
veinsHair-like veins branch
dichotomouslyDeciduous
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
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
gymnosperms in having vessels in 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 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
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
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• Other Gymnosperms