Nitrogen Fixation: N-fixing Plants - Cycads
Groups of Australian plants that possess N-fixing symbionts include:
- Wattles (Acacia)
- Peas (e.g. Sturt's desert pea)
- She-oaks (Allocasuarina and Casuarina)
- Cycads (e.g. Macrozamia and Cycas)
Cycads belong to an ancient order of seed plants. They do not develop root nodules, instead cyanobacteria ( Anabaena or Nostoc) infect root cortical cells causing vesicles to develop in which the cyanobacteria live and fix nitrogen. The infection process causes roots to develop a coral-like appearance (hence coralloid roots). Some lichens and Azolla (an aquatic fern) also develop symbioses with N-fixing cyanobacteria.