Asexual reproduction involves only one parent so there is no genetic variation and all offspring are clones of each other and the parent. This method of reproduction is much quicker than sexual reproduction and is very beneficial in environments which don’t vary.
However, in environments that change rapidly, all of these clones are susceptible to the same diseases and adverse conditions. Many plants naturally reproduce asexually (such as strawberries using runners). Humans can also induce plants to reproduce asexually by taking and planting cuttings that will grow into clones of the parent plant.
But for the moment, let’s take a look at how plants reproduce sexually. (So just to clarify: plant reproduction is the production of new offspring in plants, which can be accomplished by sexual or asexual reproduction)
The sexual organ of a plant is the the flower. The gametes of flowers are pollen (male) and ovules (female) and the process where pollen from one flower is transferred to another, is called pollination. Plants have evolved two subtly different forms of a pollination: wind-pollination and insect-pollination.
The process of pollen landing on a stigma is known as pollination and from then on the events do not differ between wind-pollinated and insect-pollinated plants.
Wind pollinated flowers require wind to transfer pollen from one flower to the next and therefore do not need bright petals or nectaries. Their anthers dangle in the air to catch wind currents (so that the pollen can be blown away) and their stigmas are feathery, making them more likely to catch pollen floating in the air. Wind pollinated flowers produce pollen grains that are larger and inflated to help them be carried by the wind.
Pollen grains have two nuclei and once pollination has occurred, the pollen grains first nucleus controls the growth of a pollen tube down the style towards the ovary. Once this is complete, the pollen grains second nucleus travels down this tube, entering the ovary from the bottom and fusing with the ovule in a process known as fertilisation. The fertilised ovule is called a zygote.
After fertilisation the zygote grows a tiny root (radicle) and shoot (plumule), while the rest of it becomes a food store (cotyledon). The ovule wall becomes the hard seed shell (testa) and the wall of the ovary grows into a fruit that surrounds the seed(s).
The seed now waits to be dispersed, which can occur by many methods (e.g. animals eating the fruit and egesting the seeds elsewhere, wind blowing seeds away). Once the seeds land in soil and in their desired conditions, they will germinate and grow into new plants.
And that’s it – pretty straightforward stuff!