Angiosperm Reproduction A Botany Application

Background

Through the span of geological time, major groups of vascular plants have risen to dominance, only to decline to small groups within the flora of the Earth The Angiosperms or flowering plants are the group that is now in total dominance on our planet

We live in the "Age of the Angiosperms" We live in the "Age of the Angiosperms". There are more than 250,000 species, grouped into 12,500 genera and about 300 families Angiosperms dominate almost every terrestrial habitat – except the tundra and northern coniferous forest

Because of their abundance and distribution, Angiosperms are a major part of the environment of other organisms They have a huge effect on other organisms, especially those that eat them Herbivorous mammals have dramatically increased in numbers with the worldwide spread of grasses  

The success of Angiosperms is directly related to their flowers – or reproductive structures   Many flowers have bright colors, attractive shapes, and pleasant aromas

These features help to ensure successful sexual reproduction as they attract organisms Also, Angiosperms have a way of dispersing its seed which gives it the ability to move great distances

Parts of a Flower

Angiosperms are classified by the structure of their flowers The parts and the arrangement of those parts is an important identification key

Receptacle - the top of the stem that supports the flower Sepals - collectively they are called the calyx (CA) They are the outermost floral parts and are usually leaf-like and green They enclose the bud of the flower

Petals - collectively they are called the corolla (CO)’ They are just inside the sepals, petals are usually delicate and brightly colored in order to attract insects

Stamens - collectively they are called androecium (A) Word origin andro means “male” They are the male reproductive parts of the flower and are located inward from the sepals and petals

Stamens are comprised of: Anther - the sac-like part which contains the pollen Filament - the stalk that connects the anther to the flower

Anthers can be attached to the filament in a number of ways:

Pistils - collectively are called the gynoecium (G) Word origin gyno means “female” They are the female reproductive parts of a flower They are located in the center of the flower

Pistils are generally are comprised of: Stigma - the pollen-receptive part at the top. The surface of the stigma is sticky which allows it to trap pollen grains Style - the stalk that connects the stigma to the ovary

Ovary - the enlarged section at the base where egg cells are produced Carpels are the basic unit of the ovary There is one seed and one stigma for each carpel

Arrangement of Flower parts

Flower parts are normally arranged in four concentric circles called whorls

The sepals protect the developing flower and make up the outermost whorl The petals are usually brightly colored and make up the next inside whorl

The stamen is found in the next whorl and contains the anther and its filament The innermost whorl contains carpels – the basic ovary unit

Some flowers may be missing some of basic flower parts Complete flowers have all four flower parts: sepals, petals, stamens, and pistils Incomplete flowers are missing 1 or more of the flower parts

A perfect flower will have a stamen and a pistil An imperfect flower will be missing a stamen or pistil perfect imperfect imperfect

Flower parts by multiples

A monocot will typically have its flower parts in multiples of 3   3 or 6 sepals 3 or 6 petals 3 or 6 stamens 3 or 6 pistils

A dicot will typically have flower parts in multiples of 4 or 5 4, 5, 8, 10 sepals 4, 5, 8, 10 petals 4, 5, 8, 10 stamens 4, 5, 8, 10 pistils

Floral Formulas - Diagrams

A floral formula is way to show the structure of a flower using symbols  The standard set of symbols are shown below:

These floral parts will always be listed in the same order First sepals CA Second petals CO Third stamens A Fourth carpels G

The numbers of each flower part is shown using a superscript after its letter CA – Co – A - G

The numbers of each flower part is shown using a superscript after its letter CA – Co – A - G

A floral diagram is a way to show the cross-section of a flower This would be how it would appear if all of its parts were at the same horizontal level A floral diagram is a good representation of a flower

The 4 symbols representing basic floral parts:

When floral structures are fused (attached to each other) they are connected with a line on the diagram Notice the symbol on the right indicates fused petals 

Angiosperm Reproduction The End