Equisetum hybrids (Equisetaceae) are known from different localities in the British Isles but have been described so far only on morphological characters. Data on the phenolic constituents (caffeic acid conjugates, flavonoids, styrylpyrones), determined by HPLC and TLC are presented as chemical characters of the hybrids and their sympatric parents. The total detectable profile of phenolics is considered and the structures of all compounds have been proven. Their retention characteristics in a standard HPLC system are given. The hybrids tend to produce, in a single plant, characteristics of both parental taxa. These cryptic characters provide evidence in support of Equisetum hybrids.