An angiosperm is a type of plant, the most common found on Earth. All flowering plants are angiosperms, with flowers that help the plant reproduce, ultimately creating seeds from which new life springs. Angiosperms have evolved to rely on wind, insects, animals and birds as part of their reproductive process. In return, angiosperms provide fruit, vegetables and nectar.
The longevity of angiosperms vary widely, with some living hundreds of years -- trees, for instance -- while others die after only one season. These life cycles are measured in a circular fashion, from seed to seed. If an angiosperm lives for one growing season or one year, it is considered an annual. Those that have a life cycle of two years or growing seasons are called biennials, while those living three or more growing seasons are called perennials.
Annuals, like all other angiosperms, sprout from a seed. If two seed leaves sprout, the annual is a dicotyledon (or dicot), the largest group of angiosperms. If the seed sprouts one leaf, it is a monocotyledon, or monocot. Vegetative growth like roots, stems and leaves continues to develop. When the plant is ready to reproduce, it flowers. Depending on the type of plant, pollination occurs within a flower, between flowers on a single plant or between plants. The process of pollination accomplishes fertilization, fusing sperm and egg. From this, a seed contained in a protective covering or fruit is produced. After this production, the plant dies.
Similar to an annual, after a biennial sprouts from a seed it creates vegetative matter. Unlike the annual, though, the biennial does not flower. Instead, it creates food storage organs like bulbs or tubers such as potatoes to fuel future growth. Then, they go into a period of dormancy for winter. When the plant becomes active again in the next growing season, it has another stage of vegetative growth, then flowers, reproduces and dies.
Perennials may be woody or herbaceous. Both kinds sprout from seed, grow and flower. The stems of the herbaceous perennials, having no protective bark, die over the winter, but the roots survive; in the spring, new growth arises from that base. The woody perennials, with their bark, merely go into dormancy over the winter and renew their growth the following spring. Perennials do not necessarily flower every year. Some perennials don't flower for many years.
Life Cycles in Difficult Environments
Sometimes biennials or perennials are planted in climates that are not optimal for the plant. Instead of living out their full life cycle, they might only last a season. The term "bolting" is used when a plant lives out a compressed life cycle as might happen when a biennial is planted in a stressful growing environment and passes through all the stages of its life, but does it in one season instead of two. Gardeners growing biennials and perennials in unfavorable climates count them as annuals and replant them yearly.
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