Seed Plants Without Flowers (“Gymnosperms”) - Coggle Diagram
Seed Plants Without Flowers
Division Pteridospermophyta: Seed Ferns
Seeds could be extremely large,
integument was attached to the megasporangium only at the base and was
up to 11 cm long and 6 cm in diameter
in the now extinct Pachytesta incrassata.
A third group to evolve from trimerophytes was the now-extinct
progymnosperms so named because some gave rise later to conifers,
the other gymnosperms
Megaspores measured up to
300 mm in diameter
microspores only 30 mm in diameter,
Evolution of Seeds
The sheath of sterile branches must have
been important in trapping wind-blown microspores
allowed them to settle anywhere on the megasporangium.
the space at the top of the megasporangium
became the place where microspores settled,
acting as a pollen chamber or holding
Division Coniferophyta: Conifers
Conifers are never vines, herbs, or annuals, and they never have bulbs or rhizomes.
Conifer leaves are always simple needles or scales.
Leaves of most conifers are perennial.
Division Cycadophyta: Cycads
Tracheids are long and wide,
and rays are massive. Even very old stems have only a small amount of wood; most
support is provided by the tough leaf bases. A prominent pith contains secretory
Division Cycadeoidophyta: Cycadeoids
The two groups differ only in subtle details of the
differentiation of stomatal complexes and in leaf trace organization.
characters alone, cycadeoids would never be considered distinct from cycads.
however, individual cones of cycadeoids contained both microsporophylls
Division Ginkgophyta: Maidenhair Tree
very much like a large dicot tree
stout trunk and many branches, but its wood is like that of conifers.
It has “broad leaves,” but they have dichotomously branched
veins like seed ferns, not reticulate venation like dicots.
which bear most of the leaves, and long shoots.
dioecious and gymnosperms, but cones are not produced.
pairs at the ends of a short stalk and are completely unprotected at maturity.
produced in an organ that resembles a catkin, having a stalk and several
sporangiophores that each have two microsporangia
The few fossils of gnetophyte organs or tissues are only several million years old,
too recent to be of much help in understanding the evolution and ancestry of the group.
The pollen is distinctive, being spindle-shaped and having narrow ridges.
easy to recognize, and fossil pollen of this type occurs as far back as the late Triassic period
pollen has not helped reveal their origins.