The spikes on the surface of pollen grains increase the chance of the grains being part of a successful fertilization. Not all pollen grains have spikes; some have a surface covered with tiny holes while others look like a tiny tennis ball. The grains are part of the reproductive system of flowering plants. Each male flower produces thousands of grains to compensate for the fact that most fail to reach a female flower.
Pollen grains are part of the male part of a plant. To reproduce, the plant must get the pollen to the female part of the plant, known as the pistil. Wind can do this by transporting the grains, but a more reliable method is for the pollen to be carried on the body of an insect such as a bee or butterfly. As the insect flies from flower to flower, the spikes on pollen grains help them cling to the insect's body, allowing them to be deposited on a female flower. Once the female flower is fertilized, it will form seeds and reproduce.
The outer surface of the pollen grain is known as the exine and is very durable. It can survive exposure to extreme heat and strong acids and bases. This means that pollen grains can survive in harsh environments and last for a long time even when buried in sediments like mud. Environments with low oxygen levels or which are strongly acidic are best for the survival of pollen grains. Preserved pollen forms an important part of the fossil record because it provides evidence of past vegetation which contributes to an understanding of past climates.
The spikes of pollen grains are arranged in patterns which are often symmetrical. Under a microscope, the distinctive patterns reveal themselves and can be used to differentiate between different species. Scientists look for three main factors when distinguishing between different species of pollen: the number and location of the holes, the overall shape of the grain and the fine spike-like structures sticking out from the surface.
Not all structures extending from the surface of a pollen grain are simple spikes. Some of the rods support a shape such as a disc or small knob and are known as columnellae. Rods that are more like a simple spike are bacula. Rods in the shape of a club are known as clavae, while short, round rods are gemmae. Pointed spikes are classified as echinae and rods ending in a swollen head are called pila.