Some SF books that concern grass, or plantlife in general

• 'Grass' by Sheri S. Tepper
• 'The Death of Grass' by John Christopher
• 'Day of the Triffids' by John Wyndham
  
• 'After London, or Wild England' by Richard Jefferies

(Grasslands are also featured heavily in Wolf Totem by Jiang Rong, but it is not an SF book.)

---