From Wikipedia
The Private Life Of A Masterpiece

Sunflowers

(original title, in French, Tournesols) are the subject of a series of still life paintings executed in oil on canvas by the Dutch painter Vincent van Gogh. Among the Sunflowers paintings are three similar paintings with fifteen sunflowers in a vase, and two similar paintings with twelve sunflowers in a vase. Van Gogh painted the first Vase with Twelve Sunflowers, which is now in the Neue Pinakothek Museum in Munich, Germany, and the first Vase with Fifteen Sunflowers, which is now in National Gallery, London, England, in August 1888 when he was living in Arles southern France. The later similar paintings were painted in January the following year. The paintings are all painted on about 93 × 72 cm (37" × 28") canvases. An earlier series of four still life using sunflowers were painted in Paris in 1887.
Van Gogh began painting in late summer 1888 and continued into the following year. One went to decorate his friend Paul Gauguin's bedroom. The paintings show sunflowers in all stages of life, from fully in bloom to withering. The paintings were innovative for their use of the yellow spectrum, partly because newly invented pigments made new colours possible. In a letter to his brother Theo, van Gogh wrote: the sunflower is mine in a way.