Ultraviolet photograph of Epilobium palustre (Marsh willowherb) in flower.
The flowers exhibit a darker area around the centre when photographed in UV. This marking is known as a nectar guide or pollen guide as it may help insects (which can see UV light) easily find the part of the flower with nectar / pollen. In turn, this makes it more likely for the flower that it will be polinated by a visiting insect.
The flowers are very small, approx 0.5mm in diameter.They have four light pink petals with a notch in the centre edge of each petal. The seed capsules are several centimetres long and covered in short fine hairs.
Image recomposed (shifted to left and right edge added) in PS CS5
Edge of flash at top of image removed in PS CS5
Desaturated and colour toning applied in PS CS5