Angiosperms are a group of plants that have flowers and produce seeds that are enclosed within a carpel. Species within this category include herbaceous plants, shrubs, grasses and most trees. Angiosperms have adapted over the years to their environment. The particular adaptions in which angiosperms pollinate, asexually reproduce and disperse their seeds have allowed them to survive on the continent of Australia. Pollination is the transfer of pollen from the anther to the stigma. Asexual reproduction is another adaption when flowers can pollinate themselves o r are pollinated through the pollen of a plant their own species.
Wind pollination occurs when the large quantities of pollen are blown away during wind and are transported to the stigma of another flower and garminates as it travels within a tube for pollen to the ovary’s ovules. Due to the inefficiency of wind pollination, a plant has to produce large amounts of pollin. Often, wind pollinators are not bright in colour because they do not have to attract animals.
They are also not scented and do not produce nectar. Often, flowers are also grouped together in inflorenscences and have long stamens and pistils. A native Australian plant, Themeda australis (also known as kangaroo grass), uses the adaptation of wind pollination to distribute itself around Australia. It is wide in distribution and usually grows in open woodland and grassland areas. It’s colours range from green/grey when it is dying and is orange brown in the summer. The prigmentation and brightness of the colours are not necessary in attracting any animals and so therefore are not apart of the characteristics of the plant as seen in figure 2.
Another example in which a native Australian plant uses the adaptation of wind pollination is the Atriplex nummularia. It is the largest of Australia’s saltbushes and could potentially grow as much as 3 metres high and 2 to 4 metres wide. They are not attractive in colour, but the leaves have scaly coating which gives them an aesthetic silver colour. The nummilaria’s male and female flowers occur on separate plants and produces miniture flowers that are wind pollinated. The nummilaria is similar to the Themeda australis through the way that their colour scheme is similar which supports that having aesthetic visual qualities is not necessary in the distribution through wind pollination as seen in figures 2 and 4.
Animal pollinated plants are larger flowers that produce relatively large pollen in small amounts. This kind of pollen can be easily attached to pollinators that include insects, birds and mammals. The placement of Anthers and stigma is important as it must be in an ideal position for pollen transfer as animals move from one plant to another. Adaptions that animal-pollinated plants have developed include structural, visual and olfactory adaptions. Structural adaptions such as ‘landing platforms’ ensure stability for animals such as bees that may need to land.
However, depending on the pollinator, there will be some hanging flowers for those pollinators that don’t need to land. Visual adaptations include guides of nectar to help insects locate the flower’s source of nectar. Many of these guides are ultraviolet wavelengths. A lot of pollinators have preferences as to what colour a flower must be and so being aesthetically pleasing to a pollinator for a flower is important, whether it be a bright red colour or a paler, white flower (this could be due to the visual contrasts at night and is preferred by moths.). Olfactory adaptions may be necessary for pollinators with a strong taste for sweet and strong smelling flowers or for pollinators that crave the smell of dung or rotting flesh.
The Banksia marginata is pollinated mainly by nectar feeding birds and in particular, Honeyeaters. Other pollinators include small mammals such as the sugar glider and insects. The attractive yellow colour and the plants production of nectar makes this attractive to these pollinators as shown in figure 6. The Banksia marginata is also known as Silver Banksia and Honeysuckle. It typically grows in the form of a shrub or a tree. The yellow flowers are arranged in two and are fast growing. It is located in south-eastern Australia. It belongs to the plant genus of Banksia. Its structure is stable for insects to land on, yet it still free hangs for birds to be able to pollinate the flower.
After the occurrence of successful pollination, it is important that a plant disperse its seeds over as wide of a distance as it can. This provides an advantages because overcrowding is prevented and in hazardous situations where growth is affected, the plants are not isolated and there is a greater chance of survival. Water
There are species such as the Avicenna marina that relies on water dispersal. The seeds have a chance of floating either a small distance or a large distance from it’s parent. The Avicenna marina relies on water dispersal from ocean water sources. The parent tree releases seeds before a tide and then the tide carries away seeds, dispersing them for the parent tree.
A dramatic version of seed dispersal involves explosions. This is when seeds are projected from the pod at a high speed caused by the parched pod, which is contracting. An example of this is the Acacia cultriformis. The seed of this plant can be thrown up to 2 metres.
The making of new offspring with only one parent is called asexual reproduction. When plants reproduce asexually, it involves cloning new offspring using portions of the parent. When offspring are produced asexually, they are genetically identical to their parent. An example of a native Australian plant that reproduces asexually is Viola betonicifolia. Often, the plant will seed without any obvious flowering and will produce small self-pollinating flowers that do not open.
Advantages and Disadvantages of these Adaptations
All adaptions have both advantages and disadvantages. Although it is a clever way of distributing the species of plants, wind pollination is inefficient and so large amounts of pollen are needed in the process. Different methods of seed dispersal are available and so each method has positives and negatives.
The unguaranteed separation of seeds from the parent plant is a negative and isolates a species of plants. Asexual reproduction doesn’t offer variations in the genetics of the plants and often will not distribute plants over a wide area. Animal pollination is effective in the way that several adaptations allow the plants to pollinate and fertilise ovums to produce new plants.
In conclusion, reproductive adaptations have increased chances of continuity of the species in the Australian environment. This is evident through the way that different Australian plants have developed different ways to reproduce and the effectiveness of these adaptations have allowed for the increased distribution of native Australian plants. This can be seen in figures 3 and 5 in reference to the Themeda australis and the Artiplex nummularia.
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