The Passiflora or 'Passion flower' (Flos passionis) acquired its name from descriptions of its flower parts supplied in the Seventeenth Century by Spanish priests in South America, known at that time as the 'New Spain'. It was known by the Spanish as "La Flor de las cinco Llagas" or the 'The Flower With The Five Wounds.' 'Passionis' refers to (Christ's) suffering. The parts were interpreted from drawings and dried plants by Giacomo Bosio, a churchman and historian, in Rome (1609), as representing various elements of the Crucifixion.
And here's a taste of some of the symbolism:
The five petals and five sepals are the ten disciples less Judas & Peter. The corona filaments are the crown of thorns. The five stamen with anthers match the five sacred wounds & the three stigma the nails. This symbolism is not universal however, in Japan it is sometimes known as 'The Clock-faced Plant' and apparently has recently been adopted as as symbol for homosexual Japanese youths.