Button Flower Spilanthes americana var. repens (Acmella oppositifolia var. repens) Photo by Charles Macke This low-growing aquatic plant provides delightful flowers that last at least a month. The buds emerge as tiny buttons, slowly opening to display a small yellow disk of petals surrounding a central cone that becomes larger as the flower ages.  Height: Grows to 12 in. Width: Space 24 - 36 " apart. Light: Sun to part shade. Soil: Any good garden soil. Blooms: Summer.  Water Depth: Grows well at the water's edge or in bog garden. Hardy: zones 5 to 8.