Based on life span plants are classified into 3 types. They are annual, biennial and perennial  
Annual (Therophyte or Ephemerals).
A plant that completes its life cycle in one growing season. Example: Peas, maize, water melon, groundnut, sunflower, rice and so on.
Biennial.
A plant that lives for two seasons, growing vegetatively during the first season and flowering and fruiting during the second season. Example: Onion, Lettuce, Fennel, carrot, Radish, cabbage and Spinach. A plant that grows for many years that flowers and set fruits for several seasons during the life span is called perennial.
Perennial (Geophyte).
A plant that grows for many years that flowers and set fruits for several seasons during the life span. When they bear fruits every year, they are called polycarpic.
 Example: mango, sapota, etc
Some plants produce flowers and fruits only once and die after a vegetative growth of several years. These plants are called monocarpic.
Example: Bamboo, Agave, Musa, Talipot palm.

1. Food storage- Eg: Solanum tuberosum, Colocasia and Zingiber officinale.
2. Perennation/reproduction - Eg: Zingiber officinale, Curcuma longa.
3. Water storage - Eg: Opuntia.
4. Buoyancy - Eg: Neptunia.

In certain trees broad plank like outgrowths develop towards the base all around the trunk. They grow obliquely downwards and give support to huge trunks of trees. This is an adaptation for tall rain forest trees. Eg: Silk cotton tree (Bombax), White cotton tree (kapok).

Some mangrove plants like Avicennia, Rhizophora, develop special kinds of roots (Negatively geotropic) for respiration because the soil becomes saturated with water and aeration is very poor. They have a large number of breathing pores or pneumatopores for exchange of gases.

A plant that completes its life cycle in one growing season. Eg: Peas, maize, watermelon, groundnut, sunflower, neem and so on.