Serrated tussock's botanical name is Nassella trichotoma. It is also known as Nassella tussock or Yass River tussock an some texts may be refered to as Stipa trichotoma.
Serrated tussock is a long lived perennial grass growing up to 60cm in height with a base of 25cm in diameter. Plant size varies with soil fertility and location. In infertile conditions plants may only reach a height of 15cm.
Serrated tussock changes colour with the seasons. Plants remain green during summer, when other grasses have usually browned off. Plants appear purple when flowering in late spring/early summer. Once seed ripens flower heads change to a golden brown with a light green tussock base. Bleaching from frost may occur in late autumn and winter, turning the plant golden yellow in colour.
Serrated tussock is shallow rooted with an extensive network of fibrous roots occurring predominantly in the top 20cm of soil. The roots are dense, wiry and fibrous making serrated tussock very difficult to pull out, even when small.
Flowering stems emerge from the base of the plant. They are multi-branched and up to 35cm long. The purple colour of the small seeds produces an overall purplish haze to the serrated tussock seed head. Once the seeds have formed, the entire seed head will 'droop' over the tussock towards the ground.
Flowering takes place as early as late winter (August) and will continue throughout the spring (September – November). Autumn flowering has been known to occur.
Seeds take 8 – 10 weeks to mature, normally occurring throughout the spring and summer months. Once seeds are ripe, the whole flowing stem detaches from the base of the plant and is dispersed by the wind. Seed is dormant and will not germinate for about 6 months.
Serrated tussock is a prolific seeding plant. A single mature plant can produce more than 100 000 seeds per year. Seed can remain viable in the soil for many years (anecdotal reports state more than 20 years). However, germinability of seed can reduce quite rapidly, with approximately 74 - 91% of the seed bank reducing over a 6 – 12 month period.
Seedlings are weak and slow growing and are more likely to establish on bare ground with limited competition.