Marsh marigold in UV light. Marsh marigold (Caltha palustris) flowers in ultraviolet (UV) light. The bull's-eye UV pattern is a result of the flower either reflecting UV (light areas) or absorbing UV (dark areas). This pattern is known as a 'nectar guide' and is thought to attract insect pollinators that can see in UV light. This image was taken on a digital camera adapted to filter and detect UV light, resulting in a monochrome image. See image B804/4367 for the same flower seen in daylight.