Coralloid roots of N₂- fixing cyanobacteria have symbiotic association with

Cycas

The correct answer is Option (3) - Cycas

The coralloid roots of Cycas are symbiotically associated with nitrogen fixing blue-green algae, Anabaena cycadae and Nostoc punctiforme.

In the middle cortex of coralloid roots, there occurs a broad blue green zone, which is known as algal zone.

Coralloid roots are irregular, negatively geotropic, dichotomously branched coral likes roots which do not possess root hair and root caps.