The lotus flower can be seen throughout in the Buddhism temples – either as an offering or as a decoration.
The Lotus is an extremely hardy flower and is able to grow in a great many hostile conditions – mud is the one most typically referenced in Thai culture. In mud the flower can grow and the head of the lotus will be above the water.
This pattern of growth is said to represent the progress of the soul from its’ start in the primeval mud of materialism, through the waters of experience and into the sunshine of enlightenment.
There are other explanations but this is the one that I learnt when I was young and I do see the Lotus Flower grown in some extreme conditions.
An important thing for visitors to note is that you should resist the temptation to take a good sniff at any flowers that you buy for the purpose of a Buddhist offering. The flowers are being presented to Buddha and are not for your benefit.