The longer these plants live, the larger the underground part becomes, and the more difficult it is to control. Woody perennials are plants with both roots and tops that survive more than one year. Woody plants that become weeds are often called 'brush'. Most brush control in landscape plantings is done with a saw. This method is not effective in the long run because the roots of most woody species will produce vigorous regrowth from the cut stumps.
Biennial plants have a unique life cycle.
They germinate and produce a low-growing 'rosette' of foliage that produces energy that is stored in a heavy root system. At the end of the first season the top of the plant dies back to the ground. The next year the root system produces some foliage and a tall flower stalk that produces seed. Then the entire plant dies. So biennial plants have a two year life cycle.