Angiosperm Reproduction

Through time, major groups of vascular plants have risen to dominate the planet. Like the Dinosaurs they come and go with some remnant stands, the Antarctic beech, like the crocodile survived where others became extinct. Algae, Mosses & Liverworts, Club Mosses, Gymnosperms and now the Angiosperms or flowering plants are the dominant force in nature during the Eocene period.

In the “age of the angiosperms” in excess of 250,000 individual species, grouped into 12,500 Genera and about 300 families dominate almost every terrestrial habitat with the exception of the tundra regions of the planet.

Because of their abundance angiosperms exert a profound effect on all other organisms including we human beings on the planet especially those at the bottom of the food chain. Herbivores proliferated with the world wide spread of grasses, legumes, and other herbs. Our honeyeaters have evolved to feed on the nectar they supply, finches feed on the seeds while the lorikeets and pigeons feed on the fruits. Mammals like kangaroos seek out the leaves while possums feed on the buds, flowers and fruits. Then there are the myriads of insects that seek out all aspects of the plants morphology to survive.

The angiosperms owe their diverse forms and numbers directly to the successful traits of their reproductive cycles and seed distribution of their ancestors. The variation in their genes was their secret to success.

Flowers are the sexual Reproductive organs of a plant as well as the organs of locomotion for their seeds through seed dispersal. Angiosperms have diverse mechanisms to disperse their seeds, allowing the plant species to move over great distances in a relatively few generations. At home Grevillea banksii which is not native to my area has migrated about 20 meters in 10 years covering 3 generations.

Flower Morphology is also the key tool used for classification of angiosperms. The parts and arrangement of those parts are important structures in using identification keys for identification.

1. Receptacle – The receptacle is found on top of the pedicel and supports a flower. The receptacle forms a cup the hypanthium, usually from which most of the flower parts arise. It is may not be a significant or obvious part of the flower.

2. Sepals – The sepals are collectively known as the calyx. They are usually the lower green parts of the floral parts and are usually leaf like in structure. The sepals usually enclose the flower bud and may be caducous shortly after the bud begins to open.

3. Petals – The petals are collectively known as the corolla. They are found on the apical side of the sepals. The petals are usually more delicate than the sepals, are often brightly coloured and prominently held to attract pollinators.

* Sepals and petals together are called the perianth

* Tepals – are usually found on monocotyledon plants. They are a result of the sepals and petals being identical or very similar that they are difficult to distinguish apart.

* Actinomorphic sepals and petals are capable of being dissected into equal parts on several planes. They are more frequently referred to as regular flowers. 

* Zygomorphic sepals and petals can be is where the calyx or corolla are capable of being divided into equal parts through only along one longitudinal plane. They are more frequently referred to as irregular flowers.

* Stamens – are the filaments and anthers and are collectively known as the androecium of the flower. They are the male reproductive parts and are located on the hypanthium, between the stigma and the perianth or on the petals. See glossary pages 50-52.

* The anther is the pollen bearing receptacle of the stamen. The anthers are attached to the apex of the filaments in different manners. Basifixed is where the anthers base is attached to the filament. Dorsifixed is where the anthers are elongated and are attached in the middle and adnately fixed is where the anthers are attached parallel to the filament for at least part of their length. See glossary pages 50-52.

* The filament is the fine connecting conduit between the anther and its attachment the rest of the flower. See glossary pages 50-52.

* The anther attachments to the filament vary and include Basifixed, dorsifixed and adnately fixed. See glossary pages 50-52.

* Stamens that are attached to the hypanthium take their name from the position they take in relationship to the petals. They consist of filaments attached alternatively to the petals, opposite to the petals and not related. See glossary pages 50-52.

* The stamens that are not attached to the hypanthium maybe attached to the corolla or pistil and are known as Epipetalous or Gynandrous respectively.

Epipetalus stamens are attached to the petals,

Gynandrous stamens are attached to the corolla or to the pistil. The stamens may be fused together or free as per the drawing.

5. Pistils – collectively are often called the gynoecium. The female reproductive parts of a flower, the pistil, is located in the center of the flower. A gynoecium may be a single pistil or many pistils, but pistils generally are composed of:

* Stigma – Is the pollen receptor at the apex of the pistil. 

* Style – Is the conduit between the ovary and the stigma. 

* Ovary – the enlarged portion at the base of the pistil which houses the unfertilized eggs.

* Each carpel will eventually produce a seed

The basic unit of the ovary is the carpel.

The number of carpels in a pistil can be determined by counting the number of stigmas or styles (each carpel has one), or by making a cross-section of the ovary and counting the number of partitions.

Gynoecial types based on fusion

Ovary attachment is either Superior or Inferior

The flower is hypogynous if the ovary is situated above the calyx and there is no floral cup around it. The ovary is superior. See glossary page 16.

The flower is perigynous if the ovary is situated within (and free from) a floral cup or hypanthium. The ovary is superior. See glossary page 16.

The flower is half inferior if the ovary is situated partially below the calyx and partially above the calyx. See glossary page 16.

The flower is epigynous if the ovary is situated below the calyx. The ovary is inferior. See glossary page 14 & 16.

Some flowers do not have all of the basic parts.

* Complete flowers have sepals, petals, stamens, and pistils. The flower below is complete because it has all its organelles.

* Incomplete flowers are missing one of more of the four basic parts. The flower below is incomplete because the sepals are missing.

The incomplete flower is missing one of the four crucial parts like the sepals, petals, stamens or pistils

* Perfect flowers have both stamens and pistils. The flower above is a perfect flower because it has both its male and female reproductive organs.

The perfect flower has both stamens or pistils in the same flower.

* Imperfect flowers have either stamens or pistils, but not both however male flowers may have a rudimentary infertile carpel while female flowers may have infertile stamens without anthers known as staminodes. The flowers below are imperfect because one lacks the female reproductive organs and one lacks the male reproductive organs. Some imperfect male flowers have Stamens and an infertile rudimentary ovary while some imperfect female flowers may have staminodes or filaments without anthers or with filaments and anthers without pollen.

Imperfect flowers have either the stamens or the pistils.

* Monoecious plants have imperfect flowers with both male and female flowers growing on the same plant.

* Dioecious plants have imperfect flowers with the male flowers growing on different plant to the females.

Inflorescence Arrangement – The arrangement of the flowers on a plant. Flowers with only one flower per stalk are called solitary flowers. The main supporting stalk of several flowers (the inflorescence) is called a peduncle. The stalks supporting single flowers of the inflorescence are called pedicels. The individual flowers of the inflorescence are called florets.

Determinate inflorescences have the oldest flower at the top of the plant with younger flowers under it. Indeterminate inflorescences have the youngest flowers at the top of the plant with older flowers below.

Elongated inflorescences

* Spike – elongated inflorescences with flowers along the central axis that are sessile (do not have pedicels). See glossary page 44-46.

* Raceme – elongated inflorescences with simple pedicels along the central axis. See glossary page 44-46.

* Panicle – elongated inflorescences with branched branches along the central axis. See glossary page 44-46.

Flat-topped inflorescences

* Corymb – flat-topped inflorescences with the pedicels of different length.  See glossary page 44-46.

* Head – rounded or flat-topped cluster of sessile flowers.  See glossary page 44-46.

* Umbel – inflorescence having several branches arising from a common point at the end of the peduncle.  See glossary page 44-46.

* Compound Umbel – If the branches end in flowers, it is a simple umbel. If the branches branch again before reaching the flowers, it is a compound umbel.  See glossary page 44-46.


1. There are more than 250,000 species of Angiosperms
2. The success of the Angiosperms as a group is believed to be as a

 direct result to their ancestors flowers and variation in genes. 
3. Flowers are organs of sexual reproduction and organs of

locomotion by means of seed dispersal. 
4. All flower parts arise from the hypanthium at the top of the

5. Collectively, the sepals are called the calyx.
6. Sepals and petals together are called the corolla.
7. Collectively, the stamens are the filaments and anthers. 
8. Collectively, the pistils are the ovary, style and stigma
9. A complete flower has sepals, petals, stamens and pistil
10. A perfect flower has both male (stamens) and female (pistil)

 reproductive parts. 
11. Monoecious plants have imperfect flowers with both flower sexes

 growing on the same plant. 

12. Dioecious plants have imperfect flowers with only one flower sex

 growing on a single plant.

13. An arrangement of flowers on a plant is called an inflorescence

14. The sepals and petals of a “regular” flower can be divided into

 equal parts along several planes
15. The anthers are sac-like flower parts containing pollen. 
16. The basic unit of the ovary is the receptacle or hypanthia. 
17. An ovary is superior if it is situated above the calyx. 
18. The individual flowers of an inflorescence are called florets
19.  Indeterminate inflorescences have the youngest flowers at the

 top while determinate inflorescences have the oldest flowers at the top. 
20. A panicle is an elongated inflorescence with branched branches along the central axis. 
21. If the branches of an umbel end in flowers, it is a simple umbel.

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