This coloured scanning electron micrograph of knotweed (Polygonum) pollen, which is about 50 micrometers in diameter, clearly shows the striking three-dimensional sculpturing of the grain. Its surface is made up of short columns called ‘baculae’. Some are fused at the top to form an irregular mesh of walls or ‘muri’. Others stand free and are visible here as wart-like protrusions. The resulting rough surface probably helps the pollen grains to stick to insects.