Most familiar gymnosperm phylum
Pines, spruces, firs, cedars, and others
- Coastal redwood - Tallest living vascular plant
- Bristlecone pine - Oldest living tree
Found in colder and sometimes drier regions of the world
Conifers are sources of important products
- Timber, paper, resin and taxol (anti-cancer)

Pines

More than 100 species, all in the Northern hemisphere
Produce tough needlelike leaves in clusters
Leaves have thick cuticle and recessed stomata to retard water loss
Leaves have canals with resin to deter insect and fungal attacks

Pine Reproduction

Male Gametophytes (pollen grains)

Develop from microspores in male cones by meiosis

Female Pine cones form on the upper branches of the same tree

Female cones are larger and have woody scales
Two ovules develop on each scale
Each contain a megasporangium that is known as the nucellus

Female Pine Cones

The nucellus is surrounded by the integument

Micropyle : small opening at end of integument
Seed coat forms from a layer of integument

One megaspore mother cell within each megasporangium forms 4 megaspores via meiosis

3 megaspores breaks down
1 slowly develops into a female gametophyte via mitosis

Female Gametophyte

Female gametophyte has archegonia at the micropylar end
Each archegonium has a large egg

Fertilization

Female cones usually take 2 or more seasons to mature
During the first spring, pollen grains drift down between open scales
- Pollen grains drown down into microphyle
- Scales close
A year later, female gametophyte matures
- Pollen tube is digesting its way through
- Mature male gametophyte has 2 sperm
15 months after pollination, pollen tube reaches archegonium and discharges contents
- 1 sperm unites with egg = zygote
- Other sperm degenerates

Cycads (Phylum Cycadophyta)

Slow-growing gymnosperms of tropical and subtropical regions
Sporophytes resemble palm trees
Female cones can weigh 45kg
Have largest sperm cells of all organisms

Gnetophytes (Phylum Gnetophyta)

Contain 3 (unusual) genera

Welwitschia
Ephedra
Gnetum

Ginkgophytes

Only one living species remains

Ginkgo biloba

Flagellated sperm

Dioecious

Male and Female reproductive structures form on different trees

Angiosperms

Flowering plants
Ovules are enclosed in diploid tissue at the time of pollination
Carpel, a modified leaf that covers seeds, develops into fruit

Angiosperm Abundance

The emergence of angiosperms changed the terrain of Earth
- Previously dominated by ferns, cycads, and conifers
Unique angiosperm features aided abundance
- Flower production, insect pollination, broad leaves with thick veins

Angiosperm origins are a mystery

Oldest known angiosperm in the fossil record is Archaefructus

125 million years old
Unlikely to have been the first angiosperm
Lack sepals and petal

Flowers house the Gametophyte Generation

Flower Morphology

Modified stems bearing modified leaves
Primordium develops into a bud at the end of a stalk called the **pedice**l
Pedicel expands at the tip to form a receptacle, to which other parts attach
Flower parts are organized in circles called whorls

Flower Whorls

Outermost whorl - sepals

Second whorl - petals

Third whorl - stamens

Innermost whorl - Pistil (aka Carpel)

The Carpel

Carpel has 3 major regions

Ovary - swollen base containing ovules
- Later develops into a fruit
Stigma - tip where pollen lands
Style - neck or stalk

Double Fertilization

A single diploid megaspore mother cell in ovule undergoes meiosis

Produces 4 haploid megaspores
- 3 disappear
- Nucleus of remaining megaspore divides mitotically

Embryo Sac

Daughter nuclei divide to produce 8 haploid nuclei in 2 groups of 4

2 nuclei ( 1 from each group of 4 ) migrate toward center
- Function as polar nuclei - may fuse
Cell closest to the micropyle becomes the egg
2 other cells are synergids
Antipodals are the 3 cells at the other end - they have no function

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-Integuments become the seed coat

-The 8 haploid nuclei in 7 cells make up the female gametophyte

Also known as the embryo-sac

Pollen Production

Pollen production occurs in the anthers

It is similar but less complex than female gametophyte formation
Diploid microspore mother cells undergo meiosis to produce 4 haploid microspores
Binucleate microspores become pollen grains

Pollination

Mechanical transfer of pollen from anther to stigma
May or may not be followed by fertilization
Pollen grains develop a pollen tube that is guided to the embryo sac
One of the 2 pollen grain cells lags behind
- This generative cell divides to produce two sperm cells
- No flagella on sperm

Double Fertilization & Seed Formation

One sperm unites with egg to form the diploid zygote
- New Sporophyte
Other sperm unites with the 2 polar nuclei to form the triploid endosperm
- Provides nutrients to embryo
Seed may remain dormant for many years
Germinate when conditions are favorable

Seeds

In many angiosperms, development of the embryo is arrested soon after meristems and cotyledons differentiate
Integuments develop into a relatively impermeable seed coat
Encloses the seed with its dormant embryo and stored food

How Seeds Protect Embryos

They maintain dormancy under favorable conditions
They protect the young plant when it is most vulnerable
They provide food for the embryo until it can produce its own food
They facilitate dispersal of the embryo

The Importance of the Seed Coat

Once a seed coat forms, most of the embryo’s metabolic activities cease
Germination cannot take place until water and oxygen reach the embryo
Seeds of some plants have been known to remain viable for thousands of years
Specific adaptations ensure that seeds will germinate only under appropriate conditions

Fruits

Most simply defined as mature ovaries ( carpels )
During seed formation, the flower ovary begins to develop into fruit
It is possible for fruits to develop without seed development
- Bananas are propagated asexually