Ultraviolet Flowers: Drosera longifolia

Drosera longifolia L.

Droseraceae

Visible light

UV light
(U-360 + BG-38, SB-140)

False-Colour Composite
UV=blue, Blue=green, Green=red

All images: Nikon D70 @800 ISO, UV-Nikkor 105 mm f/4.5

The Great Sundew plant faces a real challenge, since it is carnivorous and catches insects with its sticky leaves, but at the same time, it needs to attract pollinators to the flowers. One solution apparently is to "signal" at different wave lengths. Thus, the leaves are yellowish green with red glandular hair on them, and these hairs exude a viscous fluid at their tips. This fluid reflects mainly in the visual range, as does the leaf blade itself. For any insect with UV-enabled vision, the leaves would appear bright red with shining drops along the perimeter. On the other hand, the flower is mainly absorbing UV, but the nectaria strongly fluoresce in UV, so the flowers to the insects might appear bright yellow with shining blueish nectaria inside.

Sundew, a plant confined to bogs and wet habitats, only opens its flowers in bright sunlight, and concurrently, the sticky hairs develop their luring bright drops of viscous fluid. Evidently the clever scheme works well to the plant's satisfaction albeit not to the benefit of the insects being trapped and digested.