Angiosperms

Sunflowers are flowering plants or angiosperms. Spaces Images/Blend Images/Getty Images

Angiosperms, or flowering plants, are the most numerous of all the divisions in the Plant Kingdom. With the exception of extreme habitats, angiosperms populate every land biome and aquatic community. They are a major food source for animals and humans, and are a major economic source for the production of various commercial products.

Flowering Plant Parts

The parts of a flowering plant are characterized by two basic systems: a root system and a shoot system.

The root system is typically below ground and serves to acquire nutrients and anchor the plant in the soil. The shoot system consists of the stems, leaves, and flowers. These two systems are connected by vascular tissue. Vascular tissues called xylem and phloem are composed of specialized plant cells that run from the root through the shoot. They transport water and nutrients throughout the plant.

Leaves are an important component of the shoot system as they are the structures through which plants acquire nutrition by photosynthesis. Leaves contain organelles called chloroplasts that are the sites of photosynthesis. Gas exchange needed for photosynthesis occurs through the opening and closing of tiny leaf pores called stomata. The ability of angiosperms to shed their foliage helps the plant to conserve energy and reduce water loss during cold, dry months.

The flower, also a component of the shoot system, is responsible for seed development and reproduction.

There are four main flower parts in angiosperms: sepals, petals, stamens, and carpels. After pollination, the plant carpel develops into fruit. Both flowers and fruit are often colorful in order to attract pollinators and animals that eat fruit. As the fruit is consumed, the seeds pass through the animal's digestive tract and are deposited at a distant location.

This allows angiosperms to spread and populate various regions.

Woody and Herbaceous Plants

Angiosperms can be woody or herbaceous. Woody plants contain secondary tissue (bark) that surrounds the stem. They can live for several years. Examples of woody plants include trees and some shrubs. Herbaceous plants lack woody stems and are classified as annuals, biennials, and perennials. Annuals live for one year or season, biennials live for two years, and perennials come back year after year for many years. Examples of herbaceous plants include beans, carrots and corn.

Angiosperm Life Cycle

Angiosperms grow and reproduce by a process called alternation of generations. They cycle between an asexual phase and a sexual phase. The asexual phase is called the sporophyte generation as it involves the production of spores. The sexual phase involves the production of gametes and is called the gametophyte generation. Male and female gametes develop within the plant flower. The male microspores are contained within pollen and develop into sperm. Female megaspores develop into egg cells in the plant ovary. Angiosperms rely on the wind, animals, and insects for pollination. Fertilized eggs develop into seeds and the surrounding plant ovary becomes the fruit.

Fruit development distinguishes angiosperms from other flowering plants called gymnosperms.

Monocots and Dicots

Angiosperms can be divided into two main classes depending on seed type. Angiosperms with seeds that possess two seed leaves after germination are called dicots (dicotyledons). Those with a single seed leaf are called monocots (monocotyledons). These plants also differ in the structure of their roots, stems, leaves, and flowers.

Monocots and Dicots
 RootsStemsLeavesFlowers
MonocotsFibrous (branching)Complex arrangement of vascular tissueParallel veinsMultiples of 3
DicotsTaproot (single, primary root)Ring arrangement of vascular tissueBranching veinsMultiples of 4 or 5

Examples of monocots include grasses, grains, orchids, lilies, and palms. Dicots include trees, shrubs, vines, and most fruit and vegetable plants.