We see a huge variety of plants all around us. Among which some are terrestrial and some are aquatic plants. Despite this fact, all plants have the same parts and the same functions; they appear unique with different types of roots, stem, leaves, flowers, fruits, seeds, etc. There are different ways we can classify plants. In this lesson, we will classify plants according to their growth habits and seasonal growth cycle.
Let us start by first defining the term 'growth habit'.
In horticulture, the term growth habit refers to the shape, height, appearance, and form of growth of a plant species. Both genetic and environmental factors play an important role in the growth habit of plants. From an evolutionary perspective, growth habits are responsible for survival and adaptation of plants in various habitats, thus increasing the chances of successfully passing on the genes to the next generation. If we consider plants, based on their height, some are too short while some are too tall to climb. Other than height, the thickness and texture of the stem may also vary. For example, short plants have greenish, soft, and tender stems, while big and tall plants or trees have thick, strong, and woody stem which are hard to break.
Based on the growth habit, plants are broadly categorized into five groups: herbs, shrubs, trees, climbers, and creepers.
Trees
Trees are tall, big, and strong plants. They usually live for several years. They have a very thick, woody, and hard stem called the trunk. The trunk is the main stem of the tree and gives rise to many branches that bear leaves, flowers, and fruits. Some trees have bright flowers for a few months, others give us fruits. Many trees have leaves all round the year while others shed their leaves in winter. Examples of trees are banyan, mango, apple, teak, palm, oak, and maple.
Shrubs
Shrubs are medium-sized, woody plants taller than herbs but shorter than a tree. Shrubs are also called 'bush'. Compared to trees, shrubs have multiple stems and shorter height. Their height usually ranges between 6-10m. Features of shrubs are bushy, hard and woody stems with many branches. Unlike herbs, they have a woody stem above the ground. Although stems are hard they are flexible but not fragile. Generally, shrubs are perennial i.e. they live for more than two years. Rose, hibiscus, acacia, lavender, and periwinkle.
Herbs
Herbs are very short plants with no persistent woody stems above the ground. Their stems are soft, green, and delicate. They do not usually live for a long time. They complete their life cycle within one or two seasons. Generally, they have few branches or are branchless. These can be easily uprooted from the soil. Herbs have savory or aromatic properties that are used for flavoring and garnishing food, for medicinal purposes, or for fragrances. Some common herbs are parsley, rosemary, thyme, coriander, mint, spinach, and basil.
Climbers
Climbers have a very thin, long, and weak stem that cannot stand upright, but they can use external support to grow vertically and carry their weight. These types of plants use special structures called tendrils to climb. Some examples of climbers are pea plant, grapevine, sweet gourd, money plant, bean, cucumber, etc.
Creepers
As the name suggests, creepers are plants that creep on the ground. They have very fragile, long, thin stems that can neither stand erect nor support all its weight. Examples of creepers include watermelon, pumpkin, sweet potatoes, etc.
As we continue to grow and change throughout our entire lives, plants also have different patterns of growth and development with seasons. This is called the seasonal growth cycle and it can be influenced by several factors like temperature, moisture, and sunlight. Depending on these factors, plants regulate their developmental processes. Seasonal growth cycles are determined by where plants live, how they reproduce, and the role they play in their environments.
Based on the seasonal growth cycles, there are three types of plants: annuals, biennials, and perennials.
Annuals
Any plant that completes its life cycle in a single growing season is classified as an 'annual'. The season may last from a few weeks to a few months. During this time, the plant will develop roots, stems, and leaves before it dies. Also, during this time, the plant will produce seeds. The dormant seed is the only part of an annual that survives from one growing season to the next. The seeds are dormant i.e. they are inactive until the correct time of year, during which they will develop and go through their entire life cycles.
Examples of annuals include corn, wheat, rice, lettuce, peas, watermelon, beans, zinnia, and marigold.
There is a specific group of annual plants called 'ephemeral plants' that are short-lived plants with one or more generations per year, growing only during favorable periods (as when adequate moisture is available) and passing the unfavorable periods in the form of seeds. Ephemeral plants are usually found in the desert following a rainstorm or in a forest or a field in the early spring before dying off. In most species of ephemeral plants, the seed coats contain a growth inhibitor that can be washed off only by a copious quantity of water, thus preventing germination after only a brief shower.
Biennials
Any plant that completes its life cycle in two growing seasons is classified as a 'biennial'. During the first growing season, biennials produce roots, stems, and leaves; during the second growing season they produce flowers, fruits, and seeds, and then they die. Sugar, beets, and carrots are examples of biennials. Biennial plants produce seeds during the second year of growth, which will later become new plants the following year, perpetuating this two-year life cycle.
Perennials
Some plants do not die every year or every other year. These are common trees and shrubs. Perennials persist for many growing seasons. They must have structures that allow them to survive through different seasons. This sometimes means that the plant must survive extreme changes in temperature or water. There are two main categories of perennials: herbaceous and woody.
Herbaceous plants have a limited flowering period (usually during the summer) and survive the dormant season (usually the winter) through a variety of adaptations. Generally, the top part of the plant will die back or become dormant in the winter, and the underground part will survive. This can be done by maintaining roots, rhizoids, bulbs, or tubers.
Woody plants include trees. There are two main categories of woody perennials: deciduous and coniferous. Deciduous trees are those that lose their leaves all at once. This is seen in many trees in the fall. The leaves of deciduous trees may first turn vibrant shades of yellow, red, and orange before falling off the tree. The tree will then grow back new leaves in the spring when the environment is much better for growth and reproduction. Coniferous trees do not lose all of these leaves at once. These are also called evergreen trees because of the adaptation of not losing leaves all at once. Their leaves are usually called pine needles, as they don't look much like the traditional leaves that we know. It is important to note that conifers do lose their needles, but it is done throughout the year rather than all at once like deciduous trees.
