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Chapter 22 – Plants with
Seeds
Courtesy of Mr. B.
GYMNOSPERMS: Non-Flowering
Seed Producers
Transition from Ferns to Land Plants
Medullosa – the seed fern
Gymnosperms began to dominate landscapes as climates becam
drier at the end of the Paleozoic era 245 mya
Gymnosperms appear in the fossil record much earlier than
flowering plants, and they:
1. Lack enclosed chambers in which seeds develop.
2. Are grouped into four divisions:
3. Cycadophyta, Ginkgophyta, Gnetophyta and
Coniferophyta.
GYMNOSPERMS:
Plants with seeds that are not enclosed within a fruit, derive their
name from the Greek words gymnos (naked) and sperma (seed).
In this plant group, the seeds are produced on the open surface of
a scale. Unlike flowering plants, the gymnosperms do not form
true flowers or fruits. There are four divisions of gymnosperms.
Examples of gymnosperms include cycads, ginkgo, conifers and
gnetops.
Kingdom Plantae - Plants
Subkingdom Tracheobionta -- Vascular plants
Superdivision Spermatophyta - Seed plants
Division Cycadophyta - Cycads
Class Cycadopsida
Order Cycadales
Family Cycadaceae
Genus Cycas- cycads
Evolutionary advancements of Gymnosperms over the ferns and allies:
1.
Seeds
2.
Lack of dependence on water for fertilization (air-borne pollen)
3.
Progressively more dominant sporophyte
4.
Life Cycle
a.
5.
In the gymnosperms and the flowering plants, the sporophyte
generation is dominant with the gametophyte contained in and
dependent on the sporophyte.
Vascular System
a.
They do have a well-developed vascular system of xylem and
phloem and have true roots, stems, and leaves.
b.
The vascular tissues are significantly more efficient and effective
than the vascular systems of the seedless plants such as the ferns.
c.
Gymnosperms are usually woody plants. The xylem form the
wood if a tree and the phloem tissues are part of the bark (along
with cork). The formation of wood from secondary growth is the
reason that some sporophytes can reach such large sizes.
Cycadophyta
Class Cycadopsida
Order Cycadales
Cycadaceae
Cycas sp.
The Cycad – a fernlike gymnosperm.
Note the cone, or strobilus
The Gymnosperms
Male cones of
Pinus nigra
•Unlike the seedless vascular plants, conifers are more
prevalent in cooler regions and in desert habitats.
• leaf curled to reduce water loss
• evolved cold hardiness
Female cones of
Pinus nigra
The Gymnosperms
Gnetophyta
With angiosperm-like broad
leaves, but still retaining cones,
the Gnetophytes are another very
close link to the Angiosperms
Ephedra viridis
Female cones
More
Gnetophytes!
All bear cones, with
naked seeds, which
is an adaptation over
the ferns, that
produced spores
Welwitschia mirabilis
growing in the desert
Ginkgophyta
Ginkgo biloba
The link between
gymnosperms and
angiosperms (note the
fleshy seed)
Monocot vs. Dicot Seeds
Corn
Bean
Seed coat
Stored food
(Endosperm)
Embryo
plant
Monocot Seeds
Monocot
seeds have:
Endosperm
seed coat
endosperm
cotyledon
coleoptile
One
cotyledon
radicle
Dicot Seeds
Dicot seeds have:
No
endosperm
at maturity
Two
cotyledons
Seed coat
First leaves
Early root
Cotyledon
Organization of primary tissues in a young dicot stem (eg. Bean)
The primary tissues of a young monocot stem (eg. Corn)
Primary tissues of a young dicot root
Cross-section through a monocot root
Development of Seeds
Function of seed structures:
Endosperm
Nutrition for embryo
Endosperm
Cotyledon(s)
Cotyledons
Nutrition for embryo
Overall, what is the function of
a seed?
Protects
young embryo
Provides
nutrition for the
developing embryo
Allows
dispersal of the embryo
over time & space
Seed to Seedling
Angiosperms


Replaced Gymnosperms
as the dominant plant
type during the
Cretaceous Period 60
million years ago
Produce flowers, fruits,
and seeds
Flower Morphology
General Angiosperm Life Cycle
Pollination


Pollination can occur through biotic and abiotic
means (wind, water, birds, insects, etc…)
Morphological characteristics of flowers attract
specific pollinators
Insects – the Great Pollinators
Conventional
spectrum
What bees
see 
Bats as Pollinators
Fruits




Fruit. Mature ovary of
the a flower that
protects dormant seeds
and aids their dispersal
Seeds are the product
of pollination
Seeds are located
within fruits
There are many
different types of fruits
Fruit Types
Seed Dispersal


Seeds are highly
adapted to dispersal
Examples of
morphological
characteristics would
be buoyancy in fruits
(coconut) and
“wings” (maple
seeds)
While others are simply blowing in the wind….
Some seeds are
dispersed as a
result of being
eaten and mingling
with feces….