plant diversity notes

7/30/2019 Plant Diversity Notes

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Plant Diversity II:The Evolution of Seed Plants


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Overview of seed plant evolution

There were three (3) major reproductive adaptations in the

evolution of seed plants.

1) Reduction of gametophyte (Gametophytes of seed plants

are microscopic, so they can exist within the sporophyte).

2) Seeds became an important means of dispersal.

3) Pollen (Sperm cells) eliminated the liquid-water

requirement for fertilization.


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1) Reduction of the gametophyte continued with the evolution

of seed plants.

In seed plants, the very small female (1N) gametophytedevelops from spores retained in the sporangia of the (2N)

sporophyte. Why??

Delicate female gametophytes are protected fromenvironmental stress.

Embryos that are produced are also protected from stress.


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Three variations on gametophyte/sporophyte

relationships


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2) Seeds became an important means of dispersal.Seeds are resistant to environmental stress, and are multi-

cellular complex structures that consist of a sporophyte

embryo, a food supply, and a protective coat.The embryo develops from the fertilized egg (derived froma spore) retained within the sporangium.

The sperm (derived from a spore) is carried (produced by)

a pollen grain released from a sporangium.


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All seed plants are heterosporous.

Female spores give rise to female gametes; male spores give

rise to male gametes.The megasporangia produce megaspores (female) and the

microsporangia produce microspores (male).The megasporangium is enveloped by layers of tissue called

integuments. The whole structure (integuments +

megasporangium) is called the ovule.


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From ovule to seed.


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3) Pollen (with sperm cells) eliminated the liquid-water

requirement for fertilization.Pollen travels by air or on animals. It eliminates the need for

water to be present during fertilization.


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Hypothetical

phylogeny ofthe seed

plants.

Note- two

clades for

seed plants.


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Gymnosperms

Gymnosperms are vascular plants that bear naked seeds

seeds not enclosed in specialized chambers.

Mesozoic era was the age of gymnosperms

Gymnosperms were the most common plants during theMesozoic era (the age of dinosaurs).

Four phyla of extant gymnosperms

Phylum Ginkgophyta: e.g., Ginkgo biloba.

Phylum Cycadophyta: e.g., cycads.

Phylum Gnetophyta: e.g., ephedra

Phylum Coniferophyta: e.g., pines, firs, spruces


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Life cycle of a pine demonstrates the key reproductive

adaptations of seed plants

1. The tree is the sporophyte.2. Female gametophyte develops within the sporangium.3. Pollen cone has microsporangium that develops into pollen

(male gametophyte).4. After fertilization, the embryo develops and is surrounded

by food reserves and a seed coat.5. Embryo grows to produce a new sporophyte.


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The life cycle of a pine.


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Winged seed of a

White Pine (Pinus

st robus)


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Angiosperms are flowering plants that form seeds inside a

protective chamber called an ovary.

Examples:

Monocots: Orchids, lilies, grasses, palms, bamboo

(Eu)dicots: Daisies, maples, snapdragon, pea, oaks


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Angiosperms (Flowering Plants)Systematists are identifying angiosperm clades.

Originally, only:Monocots are angiosperms that possess one embryonic

seed leaf (cotyledon).Dicots are angiosperms that possess two embryonic seed

leaves (cotyledons).However, angiosperms have recently been divided into new

taxonomic groups.


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A comparison of monocots and dicots


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The flower is the defining reproductive adaptation of

angiospermsFlowers are made up of four types of modified leavessepals, petals, stamens, and carpels.a. Stamens are the male reproductive organs that produce

microspores.

b. Carpels are female reproductive organs that produce

megaspores.


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The structure of a

flower.


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A fruit is a mature ovaryProtect dormant seeds.Fruit aids in seed dispersal.

- Wind dispersal- Attachment and transportation- Consumption berries contain seeds to bepassed in feces


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Fruit adaptations that enhance seed dispersal


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Life cycle of an angiospermMature plant is the sporophyte

Some plants easily self-pollinate, but most have mechanisms

to ensure cross-pollination.

Male gametophytes reach female gametophytes byproducing a pollen tube.

Next slide: The life cycle of an angiosperm.


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Angiosperms dominated the earth at the end of the

Mesozoic era

Radiation of angiosperms represents the transition fromMesozoic to CenozoicAngiosperms and animals have affected one anothers

evolution

Coevolution is the mutual influence on the evolution of two

different species interacting with each other and reciprocally

influencing each others adaptations.e.g., Pollinator-plant relationships


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Plants and Human WelfareAgriculture is almost totally dependent on angiosperms.

Plant diversity is a non-renewable resource.

Many medicines are obtained from plant materials.


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Deforestation is an

international practice


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Deforestation


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Deforestation

in the United

States


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Fragmentation

of a forestecosystem


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A sampling of

medicines

derived from

plants

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