Flowers are epigynous in
Helianthus
In epigynous flowers, the hypanthium is fused to the gynoecium and the free parts of the sepals, petals and stamens appear to be attached at the top of the gynoecium, the ovary is inferior. The epigynous flowers are present in Asteraceae. Helianthus or sunflower belongs to Asteraceae and it has epigynous flower and an inferior ovary. So, the correct answer is 'Helianthus'.