Passiflora, the passion flower, is – perhaps unsurprisingly – a genus in the family Passifloraceae, which is itself part of the enormously varied order of Malpighiales, which includes everything from the willow to the violet by way of poinsettias. The order derives its name from that of Marcello Malpighi (1628–94): it was bestowed by Charles Plumier on the genus Malpighia, shrubs and small trees found in the American tropics, and confirmed by Linnaeus.

Malpighi was a remarkable man, and not primarily a botanist. Educated at the university of Bologna, he studied first philosophy, then medicine and afterwards physics. At various times he held chairs of theoretical medicine and of physics at the university of Pisa, and other posts at Bologna and Messina, but his academic and teaching career was interspersed with periods at home in Bologna where he served as a physician and carried out his own research.

Marcello Malpighi, by Carlo Cignani (Credit: Accademia di Belle Arti, Bologna)

He began a correspondence with Henry Oldenburg of the Royal Society in 1667, and was made a fellow (the first Italian to be thus honoured) in 1669. The Society published his two-volume Anatome plantarum (1675–9), and he continued to send them accounts of his researches in both human and plant anatomy. His Opera omnia was similarly published by the Society in 1696.

The title page of Anatome plantarum, printed at the Sign of the Bell in St Paul’s Churchyard.

The Opera omnia was printed by Thomas Sawbridge (son of George, who had a notorious business relationship with Cambridge University Press) at the Sign of the  Three Golden Fleur de Luces in the street called ‘Little-Brittain‘.

Famously, the name Passiflora was given to the flower by Spanish missionaries who were travelling in central and south America from the sixteenth century onwards. They saw in the elaborate arrangement of the flower structure the symbols of Christ’s Passion, from the Holy Lance to the Crown of Thorns, including the nails and the ten faithful apostles (excluding Judas and Peter).

P. incarnata depicted in a Dutch florilegium of 1696.

This nomenclature was confirmed by Linnaeus, who also named a number of species – there are currently over 550, to say nothing of the garden hybrids now available. (A remarkable number of synonyms was applied in the eighteenth and nineteenth centuries by savants including Jean Baptiste Bory de Saint-Vincent, Labillardière of the expedition in search of La Pérouse, Lamarck and Philip Miller.) New species continue to be discovered: P. xishuangbannaensis was found in Yunnan, China, in 2005. According to IPNI, fourteen have been found and described by the British expert and nurseryman John Vanderplank.

Passiflora xishuangbannaensis, from Yunnan.

One reason why there are so many species of Passiflora, why the genus has such a great variation of leaf shape and size, and why it is easy to hybridise, may be that it is a nectar source for many different pollinators, notably various species of Heliconia butterflies, bees, and hummingbirds – the greater the range for fertilisation, the greater the likelihood of natural variation.

Heliconia erato, the red postman, one of the butterflies which pollinates Passiflora species.

The ruby-throated hummingbird (Archilochus colubris) also feeds from Passiflora flowers.

The passion fruit comes from the species P. edulis, which is cultivated widely in its native habitats, where the fruit is eaten or pulped to produce juice. It is also grown in Australia and New Zealand, and in the Indian state of Andhra Pradesh, where the government has trialled cultivation to provide fruit in an area where there are no edible native trees or shrubs.

P. edulis, the flower …

… and the fruit.

Other (possible) uses for the plants tend to fall into the ‘don’t try this at home’ category. To quote Wikipedia on P. caerulea: ‘Often, the plant is boiled into a tea and used as medicine to relieve insomnia and allow deep, restful sleep. However, tetraphyllin B and epi-tetraphyllin B, cyanogenic glycosides (which liberate hydrogen cyanide when activated by enzymes), have been found in the leaves. It is possible to boil away most of the cyanide.’ That’s OK then …

In cultivation, the first issue tends to be hardiness. P. caerulea and its hybrids are hardy down to -10 degrees in most parts of the U.K. – there is one growing up a cottage near me which is at least twenty years old and flourishes every summer, whatever in the way of Beasts from the East the winter may have thrown at it.

A local passion-flower (sorry about the car, but this is Cambridge, I’m afraid).

The fruit, in various stages of ripeness …

… and a last lingering flower.

They do need a lot of sun, but apart from that are described by the R.H.S. as ‘easy’. I’ve never tried one (yet), because my relatively few sunny walls are already clothed, but perhaps it’s possible to squeeze one in (full height and width after 5–10 years, apparently).

For the real exotica, one needs the likes of @CUBotanicGarden, and specifically the glasshouses. I’m afraid I don’t know what these are: the foliage (of the passion flowers and others) is so dense at the moment that I don’t feel comfortable groping around to find labels, especially as it would seem a bit hypocritical, given that my current default mode is an attempted ferocious glare at all the unsupervised children picking off leaves and throwing gravel about.

If I did decide to get a Passiflora, the next problem would be which. ‘Snow Queen’, a Riverside hybrid, or something more colourful, like ‘Michael’ – but this is growing at Devon Subtropical Gardens, so hardiness may be an issue.

P. coccinea.

I could in theory grow lovely P. coccinea from seed, but I’m sure it wouldn’t be hardy either. Decisions, decisions …

The flowers of P. foetida …

… and the insect-trapping bracts.

One species I won’t go for, however, is P. foetida, or wild water lemon: beautiful flowers, but the leaves give off an unpleasant smell when crushed, and the plant produces bracts which trap insects … I have far too many carnivorous plants in my life already.

Caroline