Cyathenosin A, a spiropyranosyl derivative of protocatechuic acid was isolated from the stem pith of Cyathea phalerata Mart. Its structure was determined by MS, 1D and 2D NMR spectroscopic analyses and confirmed by single crystal X-ray analysis. Cyathenosin A is the first example of a naturally occurring compound containing a spirocyclic orthoester pyranosidic structure.