Plant life cycles

Diversity in plant form in annuals, biennials, and perennials

Plants are unique and essential to life on earth. Unlike most living things, plants make their own food from sunlight and water. Either directly or indirectly, they are the primary food source for humans and other animals. Additionally, they provide fuel, replenish the earth's oxygen supply, prevent soil erosion, slow down wind movement, cool the atmosphere, provide wildlife habitat, supply medicinal compounds and beautify our surroundings.

Many plants are familiar to us, and we can identify and appreciate them based on their external structures. How ever, their internal structures and functions often are over looked. Understanding how plants grow and develop helps us capitalize on their usefulness and take the part of our everyday lives.

Vascular plants contain xylem and phloem which are the water, nutrient and food conducting tissues. Ferns  and seed-producing plants fall into this catagory

mono- cots (eg grasses) produce only one seed lkaf (cotyledon).

while dicots broadleaf plants) have two. The vascular systems, flow ers and leaves of the two types of plants also differ.These differences will be important in our discussion of plant growth and development.

Plant life cycles:-

 A plant is classified as either an annual, biennial or perennial based on its life cycle or how many years it takes to produce flowers and seeds.

The plant starts life as a seed, which germinates and grows into a plant.

The mature plant produces flowers, which are fertilised and produce seeds in a fruit or seed pod.

The plant eventually dies, leaving seeds which germinate to produce new plants.

ANNUAL-

An annual, such as a marigold, completes its life cycle in 1 year. Annuals go from seed to seed in I year or growing season.

During this period, they germinate, grow, mature, bloom. produce seeds and die.

Summer annuals complete their life cycle during spring and summer, most winter annuals complete their growing season during fall and winter. There are both winter and summer annual weeds, and understanding a weeds life cycle is important in controlling it. Of course, in most locations in Alaska the temperature does not allow for winter annuals. Some plants that are winter annuals in warmer climates act as summer annuals in Alaska.

BIENNIAL-

A biennial completes its life cycle in 2 years. During the first season, it produces vegetative structures (leaves) and food storage organs. The plant overwinters and then produces flowers, fruit and seeds during its second season. Swiss chard, carrots, beets, sweet William and parsley are examples of biennials.

Biennials can sometimes go from seed germination to seed production in one growing season. This phenomenon is referred to as bolting. It is a common occurrence in Alaska due to the midnight sun, or long day lengths. This is one reason why spin ach, radish and beets can be hard crops to grow in Alaska. These plants bolt instead of producing a good crop of leaves or roots. This situation can also occur when plants are exposed to extreme environmental conditions such as temperature variation and drought.

PERENNIAL-

Perennial plants live more than 2 years and are grouped into two categories:

herbaceous perennials and woody perennials.

Herbaceous perennials have soft, non woody stems that generally die back to the ground each winter. New stems grow from the plant's crown each spring. A delphinium is an example of an herbaceous plant. Trees and shrubs, on the other hand, have woody stems that withstand cold winter temperatures. They are referred to as woody perennials.

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