Ragwort (Senecio jacobaea) is naturally a biennial, but changes to a perennial if constantly cut.
Ragwort is a short-lived erect herb usually growing to 450-600 mm tall, typically recognised by their bright yellow, daisy-like clusters of flowers at the tops of the stems. Peak flowering typically occurs in late January through to March.
More information can be found on the Weeds Australia website (opens in new window)