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Chapter 22: Seed Plants I: Seed Plants Without Flowers ("…
Chapter 22: Seed Plants I: Seed Plants Without Flowers ("Gymnosperms")
Concepts
Lignophytes - monophyletic group of woody plants
Spermatophytes - first seed plants
manoxylic wood - soft, spongy, parenchymatous wood
pycnoxylic wood - hard, strong wood with little parenchyma
Gymnosperms - plants with "naked ovules"
Angiosperms - flowering plants
Division Progymnospermophyta: Progymnosperms
Progymnosperms - evolved from trimerophytes
now extinct
Aneurophytales
vascular cambium
secondary growth
primary xylem of stems was a protostele
Little webbing between ultimate branches not yet called leaves
Archaeopteridales
Abundant wood
Secondary phloem
Stems had a siphonostele
Planated branch systems
Heterosporous reproduction
Evolution of seeds
integument - layer of tissue surrounding megasporangium
micropyle - hole in integument permitting sperm cells to swim to egg
pollen chamber - holding area
Division Pteridospermophyta: Seed Ferns
seed ferns appeared in the Upper Devonian Period
ring of vascular bundles surrounding a pith
long-lived vascular cambium that produced both xylem and phloem
foliage leaves of seed ferns bore seeds
Division Coniferophyta: Conifers
Never vines, herbs, or annuals
never have bulbs or rhizomes
leaves are simple needles or scales
leaves of most conifers are perennial
venation of conifer leaves is often simple
leaf veins have a tissue called transfusion tissue
All conifers have pollen cones and seed cones
trees are monopodial
wood is composed exclusively of tracheids
Two types of shoot
long shoots
short shoots
pollen cones are simple cones
seed cones are compound cones
Division Cycadophyta: Cyads
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Stout trunks with pinnately compound leaves
thick cortext with secretory ducts
long and wide tracheids
foliage leaves do not bear ovules
highly prized ornamentals
Division Gnetophyta
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Three groups
Gnetum
mostly vines or small shrubs
broad leaves
Ephedra
tough shrubs and bushes
desert regions and dry mountains
leaves are reduced and scale like
Welwitschia mirabilis
Short wide stem
Two leaves
Leaves grow perennially from a basal meristem
Gymnosperms with vessels in their wood
pollen cones are compound and contain small bracts
Division Cycadeoidophyta: Cycadeoids
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All extinct
vegetative features
individual cones contain both microsporophylls and megasporophylls
Division Ginkgophyta: Maidenhair Tree
single living species
lacks vessels and axial parenchyma
dichotomously branched veins like seed ferns
have both long and short shoots
reproduction is dioecious and gymnospermous
cones are not produced
ovules occur in pairs at the ends of a short stalk
