An anatomical study of the crown of Ranunculus acris (giant buttercup) and histopathological studies of infection of the crown by Sclerotinia sclerotiorum were carried out to assess the basis of crown resistance to this potential myco-herbicide, Resistance was largely related to morphological features of the crown, these being a thickened peripheral cortex, deposition of lignified material at the margin of infected tissue, a response to wounding, and the resistance of the crown’s dense network of vascular tissues. Together, these non-specific defence mechanisms limited infection within the crown of R. acris and enabled recovery of the plant by regeneration from the crown buds.