Classification of Weeds - 1 Based on life span

Classification of Weeds
Out of 2,50,000 plant species, weeds constitute about 250 species, which are prominent in agricultural and non-agricultural system.
Under world conditions about 30000 species is grouped as weeds.
I. Based on life span
Based on life span (Ontogeny), weeds are classified as Annual weeds, Biennial weeds and Perennial weeds.
Annual Weeds
Weeds that live only for a season or a year and complete their life cycle in that season or year are called as annual weeds.
Most common field weeds are annuals. The examples area. Monsoon annualCommelina benghalensis, Boerhavia erectab. Winter annualChenopodium album
b. Biennials
It completes the vegetative growth in the first season, flower and set seeds in the succeeding season and then dies. These are found mainly in non-cropped areas.Eg. Alternanthera echinata, Daucus carota
c. Perennials
Perennials live for more than two years and may live almost indefinitely. They adapted to withstand adverse conditions. They propagate not only through seeds but also by underground stem, root, rhizomes, tubers etc. And hence they are further classified into
i. Simple perennials: Plants propagated only by seeds. Eg. Sonchus arvensisii. Bulbous perennials: Plants which possess a modified stem with scales and reproduce mainly from bulbs and seeds. Eg. Allium sp.iii. Corm perennialsb: Plants that possess a modified shoot and fleshy stem and reproduce through corm and seeds. Eg. Timothy (Phleum pratense)
iv. Creeping perennials: Reproduced through seeds as well as with one of the following.a. Rhizome: Plants having underground stem - Sorghum halapenseb. Stolon: Plants having horizontal creeping stem above the ground - Cynodon dactylon
c. Roots: Plants having enlarged root system with numerous buds - Convolvulus arvensisd. Tubers: Plants having modified rhizomes adapted for storage of food - Cyperus rotundus
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