I painted an Eden of flowers divine  
“The sun shone in between, and all the little white flowers sparkled. … I went on painting at the risk and peril of seeing the whole show on the ground at any moment -- it's a white effect with a good deal of yellow in it, and blue and lilac, the sky white and blue.” Letter to Theo van Gogh, c.11 April 1888 by Vincent Van Gogh 
The intensity, poetics and singularity of joy that Van Gogh brought to the art of painting flowers remains unrivalled in the annals of art history. In terms of adjusted prices Van Gogh remains the highest priced artist for his paintings of flowers. His ‘Irises’ were priced at more than $100 million (adjusted) and his ‘Vase with Fifteen Sunflowers’ for more than $ 75 million (adjusted). 
Before Van Gogh flower painting was a part of Still Life painting tradition. But he changed it all. A man who painted seriously only for two years of his life changed the way we look at flowers and sunflowers specially. 
Of other artists who loved to paint flowers the name of American Georgia O’Keeffe comes at the top. Matisse painted flowers largely as part art decorativ style. His flowers carry the flat two dimensionality but are saturated with pure colours as per Fauvist tradition.
 
True to his Pop Art style Andy Warhol painted flowers as silk screen portfolios of flat color surfaces reminding about the unreality of ‘representation’.