The Padma is believed to be the central symbol in the Buddhism. Out of Eight Auspicious Symbols, the Padma or the lotus is chosen because lotus grows in the mud but blossoms without getting tainted, in the same way, the person who has the power of ignorance can only reach the enlightenment.
According to the Hindu Legends, Lord Brahma is said to be emerging from the navel of Lord Vishnu sitting on the lotus. The deity of Knowledge is also seen sitting on the flower.