Horticulture and Home Pest News is a product of the Extension Service. Here's an excerpt from the article by By Cindy Haynes, Department of Horticulture:
Monoecious and Dioecious
These botanical terms are terms used to describe the reproductive behavior of some plants.
Perfect in a botanical sense means that each flower has both male and female parts in the same structure. Lilies, roses, and apple flowers are perfect.
have male flowers and female flowers in separate structures on the same plant.
Mono means one – and monoecious is literally one house.
The same plant houses different flowers – some being male the others being female. Squash is monoecious. If you take a close look at squash flowers you can soon tell which are female because they have a tiny fruit at the base.
For obvious reasons, the male flowers don't. Knowing that only the female flowers produce fruit and that only 50% of the flowers on squash are female can save some heartache when all the flowers on the plant don't produce fruit.
house the male and female flowers on different plants.
The plant has separate male/female flowers. They have male plants with only male flowers and female plants with only female flowers.
Hollies and asparagus are dioecious.
Since only the female plants can produce the fruit, hollies must have a male plant and a female plant in close proximity.
Male holly plants are often given masculine names like Southern Gentleman, Jim Dandy, or 'Blue Prince. In the landscape, one or two male hollies are often tucked behind the female hollies to ensure pollination and fruit set and to hide the male plants that don't produce the showy fruit.
The male cultivars of asparagus are more popular with gardeners than the females because the male spears are larger— they don't waste any effort on fruit production.
Male plants can also be neater. Male ash trees don't produce the canoe paddle-like fruits of the females. Male trees of Kentucky Coffeetree, Cork Tree, and Ginkgo are popular for the same reason, i.e. no messy fruit.