From water lilies to apple trees, most of the plants you see around you today are angiosperms.
You can classify plant life into subgroups based on reproduction, and one of these categories includes the angiosperms. They are flowering plants that make seeds and fruits to reproduce.
Angiosperms: Definition in Biology
Angiosperms are vascular plants with flowers that make seeds in order to reproduce. These land plants can also produce fruit, such as apples, acorns, wheat, corn and tomatoes. Compared to gymnosperms that have naked seeds with no flowers or fruits around them, angiosperms protect their seeds.
The majority of all the plant species today are angiosperms. Take a look at what is around you, and you will see mostly angiosperms, such as flowers and flowering trees.
There are over 300,000 species of angiosperms, and they make up 80 percent of all plant species on Earth. These seed plants are capable of thriving in a variety of environments ranging from forests to prairies.
Scientists have traced the origin of angiosperms to the early Cretaceous Period by studying the fossil record. This plant group evolved about 125 million years ago, but it is not clear which seed-bearing plant was the ancestor. During the Cretaceous Period, the variety of angiosperms increased.
If you look at the angiosperm fossils from the late Cretaceous Period, then you may notice some similarities to modern flowering plants. By the start of the Cenozoic Era (and thus the start of the Tertiary Period), it becomes even easier to identify modern plants.
Scientists think that the fruits and flowers of early angiosperms are an evolutionary adaptation. Flowers and fruits allowed them to attract pollinators, so they reproduced more successfully and dispersed more widely. Flowers provided them with an evolutionary advantage that explains why they became the dominant plant species.
Reproductive Structures and the Life Cycle of an Angiosperm
You can examine the reproductive organs of an angiosperm to get a better understanding of its life cycle. Their reproductive structures are flowers.
Flowers can contain both male and female reproductive parts, but they don't always have both. Some species can fertilize themselves; other species need another plant to fertilize them through certain pollination methods like wind, water, animals or insects.
Flowering plants produce ovules in enclosed spaces called carpels, which means the female reproductive organs are in the carpels, too. A carpel includes a sticky stigma, which is an opening where the pollen is deposited, located at the end of a style, which is a tube leading to the plant ovary. The ovary has an ovule or female gametophyte.
The stalk-like stamen is the male reproductive organ in flowering plants. The stamens are usually arranged around the carpel. An anther, which looks like a sac, is located on the end of the stamen filament and produces pollen that fertilizes angiosperm eggs. The pollen is the male gametophyte. After fertilization, the ovule turns into the seed while the ovary turns into the fruit.
Pollination usually happens in two ways: self-pollination or cross-fertilization. In self-pollination, the pollen from the plant's own anthers fertilizes its ovules. The pollen simply lands on the stigma of the same flower. This creates offspring that are identical to the parents.
In cross-fertilization, pollen from a different plant fertilizes the ovules. The pollen has to move from one plant to another, and it accomplishes this by taking a ride on an insect, an animal or the wind. For example, a bee can transfer pollen from one flower to the next one. Flowers invite these pollinators by offering nectar.
Angiosperms and Gymnosperms
Both angiosperms and gymnosperms are vascular plants with seeds, but they have some major differences. Angiosperms have flowers, which gymnosperms lack.
In addition, angiosperms are a much bigger group of plants. Gymnosperms are considered older, and they make naked seeds without any protection from fruit or flowers.
Angiosperms and gymnosperms have significant reproductive differences. In angiosperms, the seeds form in the ovary of the flower. In gymnosperms, the seeds form in cones without any flowers. Although both groups of plants require pollination for fertilization, the angiosperms have more options.
The angiosperms have a reproductive advantage. Gymnosperms rely on natural pollination like storms, wind or water, while angiosperms use their flowers and fruits to attract organisms to pollinate and disperse seeds. Since they have a larger group of potential pollinators such as animals and insects, they have been more successful in taking over the Earth.
Benefits of Fruit
Imagine you bought an avocado. After eating the delicious green interior, you toss the large seed. If it lands in the right environment, the seed can develop into a new avocado tree. Avocados are angiosperms, so you are eating the ripened fruit portions when you consume them.
Angiosperms have fruit, which gymnosperms lack, and it gives them a significant advantage. Fruit provides extra nutrition and protection for the seeds. It also helps with pollination and the dispersal of seeds. Since seeds survive digestion when animals eat them, they can spread easily.
Types of Angiosperms
You can divide the angiosperms into two general categories with a few exceptions: monocotyledons (monocots) and dicotyledons (dicots). Cotyledons are the parts of the seeds that will become leaves. They provide a useful way to classify plants.
Monocots have a single cotyledon in the embryo. They also have pollen with a single furrow or pore. Their flower parts are in multiples of three. Their leaf veins are parallel to each other; they have a network of roots and scattered vascular tissue systems. Some familiar monocots are orchids, grasses and lilies.
Dicots have two cotyledons, and their pollen has three pores or furrows. They have net-like leaf veins, a vascular system in a ring, a taproot and flower parts in multiples of four or five. Dicots often have secondary growth and woody stems. Some familiar dicots are roses, daisies and peas.
Angiosperms: Examples in the Modern World
Fruits, grains, vegetables, trees, shrubs, grasses and flowers are angiosperms. Most of the plants that people eat today are angiosperms. From the wheat that bakers use to make your bread to the tomatoes in your favorite salad, all of these plants are examples of angiosperms.
The grains that you love, such as corn, wheat, barley, rye and oats, come from flowering plants. Beans and potatoes are also important angiosperms in the global food industry.
Not only do people depend on flowering plants for food, but they also use them for other items like clothing. Cotton and linen come from angiosperms. In addition, flowers provide dyes and perfumes. Trees that people cut down can be used as lumber and as a source of fuel.
Even the medical and scientific industries rely on angiosperms. For example, aspirin is one of the most popular drugs in the world, and it originally came from the bark of the willow tree.
Digitalis is a heart medication that helps people with congestive heart failure. It comes from the common foxglove flower. In some cases, a single flower can provide many drugs, such as the rosy periwinkle (Catharanthus roseus), which has different alkaloids that are used as chemotherapy medications.
Coevolution of Angiosperms
Coevolution is the process through which two species adapt to each other over time, so they influence each other. There are different types of coevolution, including:
- Predator and prey.
- Parasite and host.
Plants and insects display many examples of coevolution because of pollination. As flowering plants evolve, insects have to keep up with them and vice versa.
Predator and Prey
Most people do not think of flowering plants as prey, but there are multiple examples of the predator and prey relationship in nature that involve plants. In these cases, the predators are usually animals.
For instance, plants want seed dispersal without sacrificing all of their leaves, stems, roots and flowers. They do not want a rabbit to consume the entire plant.
Plants have developed different mechanisms to keep predators away, such as strong scents, poisons and thorns. Marigolds have a strong fragrance that rabbits and deer do not like. They also have a bitter taste that is not pleasant or appealing to animals, which makes it less likely that a deer or rabbit will want to munch on them.
Thorns and spines are some of the most effective ways for plants to stop predators. From roses to cacti, their defense structures provide animals a quick lesson on why they should not try to eat these plants. Stinging nettle's spiky hairs serve as a reminder for people not to get too close to the plant.
Parasite and Host
Sometimes angiosperms become hosts to parasites. They may have to deal with attacks from insects, diseases or other things. On the other hand, there are examples in nature of angiosperms being the parasites. Almost all of the parasitic plants that are alive today are angiosperms.
Some common examples of parasitic plants include epiphytes and vines. Mistletoe is a popular parasitic plant that grows on top of trees and shrubs. It attaches to the host's vascular system to extract nutrients and grow. This damages the tree's health because it is constantly losing water and nutrients to the mistletoe. Although they do not typically kill a tree, parasitic plants can make it weaker.
Dodder is another example of an angiosperm that is a parasitic plant. The vine can quickly take over an entire garden. It has become invasive in many parts of the country and is difficult to eliminate. Dodder usually makes small woody plants the host.
First, the vine wraps around the host and taps into the vascular system by inserting its roots into the stems. Then, it feeds on the host's water and nutrients. Dodder has small white flowers and can produce a large number of seeds.
Competition Among Angiosperms
You can find examples of competition among angiosperms every time you go outside and encounter nature. Trees spread their branches to soak up sunlight and block the rays from reaching lower plants.
Flowers try to have the most colorful petals to attract pollinators. Some plants simply crowd each other and try to take over all the available space.
Since angiosperms require pollination, they have evolved to attract pollinators like bees and birds. Each species wants to receive the maximum number of visitors, so they have developed amazing fragrances, shapes and colors to attract them.
Flowering plants are in competition with each other and all the other plants to survive.
Mutualism Among Angiosperms
Many insect and plant relationships are examples of mutualism. For instance, some acacia trees in South America have a mutual relationship with ants. The trees make nectar, which is food for the ants. In return, the ants protect the trees from other insects and predators.
They defend the trees from bugs that may eat them. Acacia trees also provide the ants a safe home in their hollow thorns. Scientists view this relationship as a case of coevolution: Both ants and the trees benefit from living together.
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About the Author
Lana Bandoim is a freelance writer and editor. She has a Bachelor of Science degree in biology and chemistry from Butler University. Her work has appeared on Forbes, Yahoo! News, Business Insider, Lifescript, Healthline and many other publications. She has been a judge for the Scholastic Writing Awards from the Alliance for Young Artists & Writers. She has also been nominated for a Best Shortform Science Writing award by the Best Shortform Science Writing Project.