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Complete Flowers: Examples, Definition & Structure

  • 0:15 What Makes a Flower Complete?
  • 1:10 Structure of a Complete Flower
  • 3:55 Examples of Complete Flowers
  • 5:20 Lesson Summary
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Lesson Transcript
Instructor: Derrick Arrington

Derrick has taught biology and chemistry at both the high school and college level. He has a master's degree in science education.

Biologically speaking, all flowers are not considered complete. In this lesson, we will learn what makes a flower complete, and examine the structure of complete flowers. We will also view examples of commonly found complete flowers.

What Makes a Flower Complete?

'A rose by any other name would smell as sweet. ' Although Shakespeare probably didn't have biology in mind when he wrote this line, we can also call a rose a complete flower in the world of biology. According to their structures, some flowers - like roses - are considered to be complete, while others are classified as incomplete.

In order for a flower to be considered complete it must have four parts: sepals, petals, stamens and pistils. Incomplete flowers lack one or more of these parts. Before we get into more detailed definitions, let's examine where you can find each part on a complete flower.

If you look at a cross section of a rosebud, you'll notice the green sepals on the outside. The sepals surround the rose's red petals, and if you carefully pull back the petals, you'll find the yellow stamens. The stamens surround the rose's pistils in the center. Moving from the outermost layer to the center, we go from sepals to petals to stamens to pistils. This order is true for any complete flower. Now, let's see what each part does for the flower.

Structure of a Complete Flower

Flowers function as reproductive structures for many plants, and each part of a complete flower helps the flower serve that ultimate purpose.

At the outermost layer, we have sepals, which are the leaf-like, usually green structures at the flower base. They function to protect the flower as it's forming. You can think of it as the armor that helps flowers survive long enough to reach reproductive maturity.

Petals are the colorful parts of the flower that function to attract pollinators. Different petal colors can attract different types of animals and insects to act as pollinators. For example, many butterfly species are drawn to flowers with red or yellow petals. Sepals and petals are often referred to as the sterile parts of the flower because they don't carry out sexual reproduction. For that step, we need stamens and pistils.

A complete flower may have one or more stamens. Stamens are male reproductive parts of a flower. Each stamen looks like a long tube with a ball on the end. The tube is called the filament, and the ball on top is called the anther. The anther produces pollen grains, which contain the flower's sperm. When pollinators come into contact with the anther, they may carry pollen grains away to fertilize a flower.

Just like with stamens, a complete flower may have one or more pistils. Pistils are the female reproductive parts of the flower. A pistil is often bottle-shaped, and it has three main parts: the stigma, style and ovary. The sticky surface on top of the pistil is called the stigma. When a pollinator rubs a flower the right way, pollen will stick to the stigma.

The style is a slender stalk that connects the stigma to the ovary. You can think of it as the neck of the bottle. Pollen grains deposited on the stigma form pollen tubes that burrow through the style to reach the ovary. The ovary is a hollow cavity that contains immature seeds called ovules - you can think of it as the body of the bottle. Once a pollen tube reaches the ovary, it deposits sperm cells, which will fertilize an egg waiting inside an ovule. The fertilized ovule develops into a seed that may one day create another plant with more complete flowers.

Also, you may hear the term carpel used instead of pistil to describe the female flower parts. While the terms can sometimes be used interchangeably (when a single carpel makes up a single pistil), that's not always the case (when multiple carpels fuse together to form a compound pistil). Now that you have a better understanding of how the parts of a complete flower work together, let's look at a few more examples.

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