Flowers look best in their natural habit. But when practicing to compose and photograph still life scenes, plucked flowers look terrific The problem is that most flowers in a vase look best when viewed from slightly above so that one can see the entire arrangement. For a still like that is photographed straight on, I find it best to put the flowers so they are more or less parallel to the plane of the camera sensor.
For this image, I clipped most of the stems and arranged the flowers facing forward. I wanted the flower in the right to be higher than the rest, so I used a water glass. Then inspired by many underwater flower arrangements I've seen, I placed one of the sunflowers in the water. As unnatural as the pose is, I actually like it.