When plants reproduce sexually (ie by forming a seed) there are three different arrangements of the male and female sexual organs in terms of their distribution on the plant. These are:
In these plants the flowers all have both male and female sexual organs. Roses are an example of a hermaphrodite plant – their flowers all contain both male stamen and female stigma so the likelihood is that the egg will be fertilised by pollen from the same flower.
These plants, which include the common hazel Cornus avellana, have separate male and female flowers but they grow on the same plant. These plants tend to rely on the wind for pollination, the very light male pollen being blown onto the female flowers.
Some plants will only bear flowers with one gender’s sexual organs. Therefore the plants can be considered male or female, and you will need one of each to obtain fruit and seed. Examples of dioecious plants are holly (Ilex species) and Skimmia japonica. If you’re hoping for berries from either of these then you will need a male and a female plant in relatively close proximity. Once a plant is a couple of years old a good nursery should be able to tell you what gender the plant is so that you can ensure you have at least one of each.
Other pollination controls
These variations in the way in which pollination occurs (when the pollen is transferred onto the female stigma) are used by plants to help control their breeding patterns. There are also many other ways in which plants control and increase their chances of successful pollination, such as:
- Opening their flowers before the leaves come to maximise wind pollination opportunities (ie so that the leaves don’t impede the progress of the floating pollen).
- Having large, protruding stigma to capture pollen as it floats past.
- The stigma and stamen on a particular plant ripening at different times or being of different lengths so they don’t touch, to encourage cross pollination between different plants.
- Bright coloured petals and scent to attract bees and other insects (or even birds or bats!) to brush against and pick up the sticky pollen from the flower, then brushing against and transferring it to the stigma.
- Trapping pollinating insects inside the flower for a period of time to maximise the chances of self-pollination (eg the Arum lily).