The classification of plants is necessary in order to study and understand plants in an orderly manner. Categorization allows for diagnosis of disease and pest problems as well as knowledge about the growth and reproduction of the plant. Classification is done in a structured way and follows specific guidelines.
Plants are categorized by growth habit. Annuals are plants that complete a life cycle from seed to flowering and then to reseeding in a growing season. After that season, which may last a year, the plant dies. Perennials continue growth for years. A perennial may flower, seed and repeat this scenario or simply take a number of years to produce seed before dying. The term "perennial" is often used to describe non-woody plants that continue living from year to year. Some perennials die back and then regrow in successive years. The term "biennials" refers to plants that complete two years or two seasons before ending their life cycle.
Structure or Form
The size, structure or form of the plant is used to classify it. Woody plants are those with hard, tough stems. Vines, shrubs and trees are examples of woody plants. A tree may be additionally grouped according to size and shape. Herbaceous plants have stems that are less tough than woody plants. In general, soft-stemmed plants are sometimes described as herbs.
Whether a plant is deciduous or evergreen further defines the perennial plants. Deciduous plants lose their leaves during the fall and winter months, and evergreen plants retain their leaves. Evergreens are further categorized according to leaf shape, such as broadleaf and needle-leaved.
Perennial plants are grouped according to the lowest temperatures that they are able to survive. Tropical plants need temperatures above 32 degrees F. Subtropical plants allow for brief exposure to below-freezing weather. Temperate plants handle temperatures significantly below freezing.
Annuals are similarly categorized. Cool-season plants tolerate short-term freeze, while warm-season crops suffer with extended cold. Cool-season crops grow best with daytime temperatures that range from 55 to 75 degrees F, and warm-season crops develop best when daytime temperatures reach 65 to 95 degrees F.
Plants are often categorized by use. A plant that is typically used for aesthetic purposes is termed an ornamental. Plants grown for food purposes are labeled fruits or vegetables. A fruit, technically, is the portion of the plant that contains the seeds; however, according to use, it is considered a fruit when it is used for a dessert. Vegetables are labeled based on their use during the main meal.