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Seed Plants 1: Seed Plants without Flowers (Gymnosperms) (Division…
Seed Plants 1: Seed Plants without Flowers (Gymnosperms)
Concepts
Lignophytes
Woody Plants
Spermatophytes
seed plants
manoxylic wood
very soft, spongy, parenchymatous wood
pycnoxylic wood
hard, strong wood with little parenchyma
gymnosperm
plants with "naked ovules"
ovules located on flat sporophylls
example: pine cones
Angiosperms
flowering plants with carpels
believed to be sporopohylls that form tube-like closed structures
Division Progymnospermophyta: Progymnosperms
Progymnosperms
third group to evolve from trimeophytes
now extinct
gave rise to conifers, cycads, and other gymnosperms
Aneurophytales
more relictual progynmospems
vary from shrubs to large trees (up to 12 m tall)
little webbing between ultimate branches
all have vascular cambium and secondary growth but primary xylem of stem was protostele.
Archaeopteridales
more derived progymnosperm
trees up to 8.4 m tall
abundant wood and secondary phloem
Pith surrounded by ring of primary xylem bundles like modern conifers and dicots
Evolution of Seeds
Integument
megasporangium surrounded by a layer of tissue
micropyle
hole in the integument that permitted the sperm cells to swim to egg
Pollen chamber
place where microspores settle
Divison Pteridospermophyta: Seed Ferns
progymnosperms
gave rise to another line of gymnospermous plants in addition to conifers
the cycadophytes ( has three divisions)
Cycadophyta
cycads (extant)
Cycadeoidophyta
cycadeoids (all extinct)
pteridospermophyta
seed ferns (all extinct)
Seed ferns
appeared in Upper Devonian
form a grade (level of evolution) not a clade (all descendants of a common ancestor)
had long-lived vascular cambium that produced both xylem and phloem
Pteridosperms
thought to evolve from aneurophytales (earliest seed ferns)
tracheid's were longer and wide enough that several rows of circular bordered pits could occur
rays were many cells wide (not just one cell wide)
very tall
large wedges
Division Coniferophyta: Conifers
diverse species (approximately 550 species)
trees of moderate to gigantic size
never vines, herbs, or annuals
never have bulbs or rhizomes
always have simple needles or scales
they are perennial (persisting for many years)
Long shoots
tiny papery leaves occur here
short shoots
produce familiar long needle leaves
simple cones
aka pollen cones
has single short unbranched axis that bears microsporophylls
Compound cones
aka seed cones
consist of a shoot with axillary buds
Cone bracts
short axis bears leaves called cone bracts rather than sporophylls
Ovuliferous scale
megasporophylls are fused laterally on the axillary bud
Suspensor
zygote doesn't immediately to form embryo, instead some of first cells elongate and push other cells deep into the megagametophyte
proembryo
develop into the embryo
Division Cycadophyta: Cycads
Frequently confused with either ferns or young palm trees
short trunk with pinnately compound leaves
short plants (less than 1 or 2 m tall)
internally similar to seed ferns
leaves do not bear ovules
produce seed cones and pollen cones but on separate plants
contains approximately 100 species
Division Cycadeoidophyta: Cycadeoids
All extinct
have vegetative features almost identical to those of cycads
individual cones of cycadeoids contained both microsporophylls and megasporophylls.
Division Ginkgophyta: Maidenhair Tree
contain single living species
looks like a large dicot tree with a stout trunk and many branches
Wood like a conifer
lacks vessels and axial parenchyma
has short shoots and long shoots
no cones produced
ovules occur in pairs at the end of short stalks and are unprotected
the exact ancestors are not known but must have been a seed fern or closely related group
abundant during Mesozoic Era
Division Gnetophyta
Contains three groups of enigmatic plants
Ephedra (40 species)
welwitschia mirabilis (only species)
Gnetum (30 species)
mostly vines or small shrubs with broad leaves similar to dicots.
gymnosperms with vessels in their wood
