They are part of the Asteraceae family, like sunflowers, Daisies and Asters.
This is the Cosmos bipinnatus, commonly known as Mexican Aster, with its broad ray florets and fine foliage of feathery leaves. In Hungarian, we call them butterfly flowers, because their petals are so delicate and easily carried by the wind.
The brightly colored flowers come in many variations, from white to different shades of pink and dark red.
Here are a few:
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