There is much more symbolism in holding a flower in your hand, even the most modest daisy, than just a blade of grass or a branch. Maybe an olive or a laurel branch could have some, but there are certainly a lot of unconscious or subconscious concepts, images, dreams, memories triggered in our mind by the mere contemplation of some beautiful flowers. Notice that I don't mean just the effect of colors but also the influence of shape and textures.
Take this bouquet I found at Las Ramblas. It is exuberant, isn't it? In what sense? I changed the colors on purpose just to see the effects playing with different channels in Photoshop. The flowers kept looking beautiful in all of them. Maybe it is just the light falling on those petals or the voluptuosity of the turgent bulbs that remind you of lips? I don't know. I finally decided to keep a touch of color but with a burnt sienna layer on top that makes it look like a canvas and much more artistic perhaps.
The hypnotic effect is still there though and I can't explain why. Can you?
Want to learn more about flowers and gardening, check Lamour et Fleurs