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Seed Plants without Flowers (Division: Seed Ferns (History (Appeared in…
Seed Plants without Flowers
Division: Seed Ferns
History
Appeared in Upper Devonian Period
Not all closely related.
They form a grade rather than a clade.
Any wooded plant with fern-like foliage that bore seeds instead of sori on its leaves.
Member of three groups under Progymnosperms:
Cycadophyta
Cycadeoidphyta
Pteridospermophyta (seed ferns)
Many resembled modern tree ferns, though others appeared as vines.
Division: Conifers
Physical appearances
Never vines, herbs, or annuals.
Leaves
Always simple needles or scales.
Perennial, lasts many years.
Leaves of
Agathis
or
Araucaria
remain even on extremely old trunks.
All are moderate to gigantic size.
Pollen :
Conifer pollen arrives before the egg is mature.
More than a year may pass between pollination and fertilization.
Massive pollen tubes slowly digests its way to the megagametophyte.
Zygote does't immediately form an embryo in conifers.
Diversity
550 species
50 genera
Extremely diverse group.
Division: Cycads
Frequently confused with either ferns or young palm trees.
Despite not being palms, they are almost exclusively tropical.
Physical appearances
Trunk covered with bark, persistent base leaves remain on the plant.
Internals are similar to those of seed ferns.
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Stems have a thick cortex with secretory ducts.
Tracheids are long and wide.
Rays are massive.
Short, less than 2m tall.
Leaves/cones
Unlike seed ferns, cycad foliage leaves don't bear ovules.
Cycads produce seed cones and pollen cones.
Pollen cones consist of spirally arranged shield shaped microsporophylls.
Diversity
Was much larger in earlier times.
9-10 genera
Around 100 species
Modern cycads are prized ornamentals in the warmer areas of the US, few withstand freezing temperatures.
Division: Maindehair Tree
Physical traits
Looks very much like a large dicot tree with a stout trunk and many branches, but its wood is like that of conifers.
Lacks vessels and axial parenchyma.
Has "broad leaves" but they have dichotomously branched veins like seed ferns.
Short shoots which bear most of the leaves, as well as a few long shoots.
Reproduction
Dioecious and gymnospermous.
Cones are not produced.
Ovules occur in pairs at the ends of a short stalk and are completely unprotected at maturity.
Pollen is produced in an organ resembling a catkin.
Contains a single living species,
Ginkgo biloba
.
Division: Gnetophyta
Contains 3 groups of enigmatic plants
Ephedra
Contains 40 species
Tough shrubs and bushes that are very common in desert regions of North America and dry mountains in South America.
Leaves are reduced and scale like.
Welwitschia mirabilis
Only one species.
The few living plants live in the deserts of South Africa or in cultivation.
Short, wide stem with only two leaves.
Leaves grow perennially from a basal meristem, becoming increasingly longer.
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Gnetum
Contains 30 species
Mostly vines or small shrubs with broad leaves similar to dicots.
Division: Cycadeoids
The 2 groups differ only slightly, Cycadeoids and Cycads.
Differences
Stomatal complexes
Leaf trace organization
Had vegetative features almost identical to cycads.
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Normally, the differences shown above would not allow for such a group to be its own.
What sets it apart?
Individual cones contain both micro and mega sporophylls.
Each ovule had a stalk/
Megasporangium was surrounded by an integument that extended out into a long micropyle.
