E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
said to have sprung up in the track made by Pilate when he went to the cross to see his title affixed [Jesus of Nazareth, king of the Jews]. It is a common trefoil, probably a native of India or Turkey. Each of the three round leaves has a little carmine spot in the centre. In the day-time the three leaves of the trefoil form a sort of cross; and in the flowering season the plant bears a little yellow flower, like a crown of thorns. Julian tells us that each of the three leaves had in his time a white cross in the centre, and that the centre cross lasts visible longer than the crosses of the other two leaves. (See CHRISTIAN TRADITIONS.)