Coralloid

Coralloid refers to a form or structure resembling coral, especially in branching or finger-like projections. In botany, it is most commonly associated with coralloid roots of cycads. Coralloid roots are short, thick near-surface roots that radiate outward like a miniature coral colony. They host colonies of cyanobacteria, particularly Nostoc, within specialized root tissues. This symbiosis supplies fixed nitrogen to the plant, which is advantageous in the nutrient-poor soils where cycads often grow. In exchange, the cyanobacteria receive carbohydrates and a protected niche from the plant. The roots can be evident at the base of the plant and may contribute to the plant’s overall nutrient economy as well as to its resilience in marginal environments.

Outside botany, coralloid is used to describe coral-like morphology in other organisms or in fossil or mineral formations. However, in common scientific usage it most often refers to the coral-like root structures of cycads. The term derives from the Latin corallium, meaning coral, reflecting the visual similarity to coral colonies.