Filler flower
A small, often many-headed flower used to fill gaps and soften an arrangement.
Also: filler
Fillers are light flowers with many small heads on branching stems. They fill the spaces between larger blooms, add texture and make a bouquet look generous. Gypsophila, known as baby's breath, is the most familiar. Others are waxflower, statice, solidago, limonium, spray chrysanthemums and the lacy umbels of ammi. Fashions change: gypsophila was long treated as a cheap extra and is now often used alone in large clouds.