When it comes to reproduction, the birds and the bees certainly have a less complicated time of it than plants do. Did you know that whether or not a plant will bear fruit or seeds is an incredibly complex process, tied to the sex of the plant? That's why some plants need a similar type of plant growing near them in order to produce desirable fruit. For example, some plants produce only male or female flowers; to produce seeds, both male and female flowers are needed. The following terms may help you understand some of the intricate aspects of plant reproduction.
These flowers have both male and female reproductive organs, meaning they can produce both pollen and seeds. The male organs, known as stamens, produce pollen. The female organs, known as pistils, contain ovaries that will eventually hold seeds if the flower is pollinated. A perfect flower can often pollinate itself if the pollen from the stamen falls onto the pistil or is brushed there by a visiting bee or other insect. Most common flowers, including African violets, roses, daffodils, potatoes, strawberries, and pears produce perfect flowers.
Sometimes a flower contains only male or female organs, so we call that a male or female flower. Since these flowers lack the full set of parts, they are considered "imperfect," and as such, cannot be self-pollinating. A bee or other insect must travel from a male flower to a separate, female flower either elsewhere on that same plant or on a nearby plant in order for there to be seeds or fruits. Plants with imperfect flowers include squash, walnut, birch, and many begonias.
Some plants can have both perfect and imperfect flowers at the same time. One flower may have both male and female parts, while another flower on the same plant has only male or female parts. These plants can produce their own fruits, but they usually produce more fruits if there is also a similar plant growing nearby to act as a pollinator. (Bees and other insects transfer the pollen from one plant to another on their body.) Some maples (Acer spp.) and smokebush (Cotinus spp.) are polygamous.
To add another level of complexity to the confusing business of plant sex, some plants themselves are either female or male in that they have only male or female flowers. These are the plants that must be planted in pairs or other multiples containing at least one male and one female in order to produce fruit or seeds. If you don't want your plant to produce seeds or fruit, look for male plants. Any good nursery or garden center should be able to help you find these.
Dioecious plants include many hollies, ginkgo (Ginkgo biloba), asparagus, and willows. For many types of holly to produce their fruits, pollinator male plants such as ‘Blue Boy' or ‘Jersey Knight' must be planted near the female plants. Because they act as pollinators, these male plants cannot bear their own fruits.
Knowing the sex of some plants is handy in other ways: Many gardeners and landscapers avoid planting female ginkgo trees, for instance, because the fruits emit a bad smell.