Thursday, 20 December 2012


Undoubtedly, one of the highlights of my time at Kew so far has been maintaining and becoming acquainted with the large Passiflora collection held in Zone 9! Passiflora is a genus containing over 500 species that are mostly found in tropical South America, and to a lesser extent in places such as North America, Southeast Asia and Australia. The simplest way I can describe them is as the tropical version of Clematis; vigorous blighters that clamber about all over the shop on tendrils, and with delightfully beautiful flowers that are consistently showy and fascinating across the genus! These amazing flowers have been captivating horticulturally-disposed eggs for centuries, as far back as the 16th century they were being lauded and praised for their beauty. Spanish Jesuit priests were convinced that these flowers symbolised the Passion of Jesus Christ, and attributed the complex flower parts to the various elements involved in the crucifixion. The Latin word passio means suffering, and this religious association continued in the naming of the genus by Linnaeus.

The stereotypical Passiflora bloom is large and showy, with a crown around the flower known as the corona that acts as an attractor and landing pad for pollinators such as bumblebees. An inner corona leads to the nectar, which the bees extract in the traditional manner with their tongues! This corona is stunted in species pollinated by hummingbirds (landing pad not required), but the floral tube leading to the nectaries is much longer, about 10cm, to account for the long beak of these graceful birds. The arrangement of the male and female flower parts is quite unique, with the male anthers pointing down towards the flower. Pollen transfers from these on to the backs or heads of bees and birds respectively, as they brush against the anthers before consequently brushing against other flowers when they cheerfully continue on their pollination rounds. The female parts are also conspicuously arranged, generally seen in threes and always standing upright as the flower opens. A period of time elapses after opening, this quirk dependent on the particular species, after which the stigma then also begins to slowly point down towards the flower. This brings it slightly closer to the action where the pollinators are drinking nectar, and enables it to better receive pollen from the slurping bees and birds. The aim of this remarkable skulduggery is to limit the chance of self-pollination, by leaving a window of time in which the pollen on the anthers can be removed by the first eager visitor. Appearing after this raises the possibility of coming into contact with pollen from another flower, which increases genetic variation and creates stronger plants in the next generation!

 In terms of cultivation, one of the most enticing aspects of Passiflora is their ability to flower well as container grown plants. The majority of the specimens in Zone 9 are growing in 5L pots and are regularly hacked back throughout the year to keep their vigorous growth in check, but in spite of this apparently rough treatment a large majority of the species flower well, and even at this time of year with the ever-reducing light levels. For growers in England, containers and a greenhouse are generally required to get near these predominantly tropical plants. There is happiness in the world however, as near-hardy specimens are available to enthusiasts in our less balmy climes, with Passiflora caerulea the hardiest for cultivation in England. This species will endure temperatures below freezing when planted in a sheltered spot and offered some protection; with good drainage the key to limping it through our cold and damp winters (wet cold quickly croaks the roots). Fortunately P. caerulea hybridises readily, and the hardiest hybrids available are those involving this species in the parentage. P. ‘Amethyst’ and P. ‘Clear Sky’ are two notable examples, but there have been over a hundred created (where there is a will, there is a way!) An unheated yet frost-free greenhouse or windowsill would obviously be an ideal situation to overwinter a container grown P. caerulea hybrid, brought in from the garden after a prune that results in at least some green leaves being left on the plant, and tied-in to four foot or so of canes to support any winter growth.
I am smitten, as this rambling on indicates! Enough jabbering, here is some Passiflora glory!
Passiflora umbilicata, a glorious specimen from Argentina and Bolivia. Pollinated by hummingbirds, it is unique amongst Passiflora as all other species pollinated in this way are either red or pink

The ripening fruit of Passiflora foetida. The Latin epithet ‘foetida’ normally relates to something foul smelling, in this case the flowers smell sweetly but the hairs on the leaves pong when disturbed

Another of the hardier hybrids, P. x violaceae, British-born in 1819 and the first hybrid ever created by crossing P. racemosa and P. caerulea. Flowering in Zone 9 for the past three months!

Many red-flowering species are difficult to maintain, but Passiflora ‘Lady Margaret’ is amongst the hardiest and flowers freely

Passiflora siamica, a rare gem from China. Last week a Passiflora expert spent almost thirty minutes in Zone 9 photographing these blooms, and actually picked three ‘to take home and dissect’! This eccentric mayhem is explained by the uniquely large number of male and female flowering parts

One of the most wonderful hybrids housed in Zone 9, Passiflora x belottii, born from a cross between P. alata and P. caerulea. Sweet smelling, very free-flowering, and the contrasting pink petals and white sepals are a thing of beauty!

Passiflora organensis with the anthers pointing downwards and loaded with pollen, ready to brush on to the head of the pollinator as they reach in to claim their nectar reward

Several of the smaller flowered species have a rich, deep purple to the undersides of the leaves. This is Passiflora vespertilio, widespread in South America and not tolerant of cool temperatures. Latin for bat is vesper, while vespertilius means ‘resembling a bat’; in this case relating to the outline of the foliage

Another dalzzling hybrid, Passiflora ‘Red Infinity’

Passiflora herbertiana is one of three species found in Australia. Aborigines eat the fruits! This chap is a real bloodhound; self-fertile, relentlessly free-flowering (sprung straight back into bloom after a recent chopping back), and very tolerant of cooler temperatures. Worth a look!

The forming fruit on a recently pollinated flower. After many failed attempts at crossing species this fruit has finally set for me! A long process ahead of seed ripening, germination and seedling growth, but Carlos is optimistic about the parents I chose and the potential hybrids

Another of the slightly hardier species, Passiflora amethystina, that flowers extremely well when grown in a pot with blooms up to 10cm across!

The foliage of Passiflora species is the most varied of any genus, often displaying dramatic lobes such as here with P. obtusifolia. This variation creates a disguise, in an attempt to bamboozle Heliconius butterflies. These beautiful creatures lay their eggs on Passiflora leaves, and the following caterpillars feed ravenously! Other defences used include hairy leaves that trap caterpillars, foliage with toxins, and nectar glands on the leaves which attract ants and wasps that will naturally predate caterpillars

Dryas iulia, the Julia Heliconian, native to Southern and Northern America and seen here at Stratford Butterfly Farm

Heliconius ismenius, the Tiger Heliconian, native to similar regions and again seen at Stratford Butterfly Farm


Jane Aston said...

I am trying an ordinary Passion Flower here in The Morvan France. We have cold winters short but can be tough. The locals use bracken to pile on top or Fuscias and such fleshy vulerable plants and it seems to work. I am trying Clematis too this year.I love those purple Passion Flowers, I am really interested in growing roses here too. Extreme short winters long summers who knows.

Jayne said...

I adore the passion flower. My sister grows it successfully outdoors in the summer, and once had it growing in a conservatory in a home where she worked. It is a real treat to have it indoors in our climate!

Susan Libertiny said...

What an amazing flower form. Thank you for sharing the details. It was a wonderful post.

Bertie Bainbridge said...

Merry Christmas all!

Wife, Mother, Gardener said...

Interesting to hear about their pollination habits. Cheery to hear that a few hardier cultivars are about. Good luck with your Passiflora babies!

Merry Christmas!

David said...

Hi Bertie,

A very interesting piece. Love the photo of P. siamica - I guess that was Dr. Vanderplank who was poking it about. Top marks for having a go at hybridising.

Can you please help me with a photo of Passiflora 'Red Fury' bred at Kew in 2010 by Carlos Magdalena (your boss?). I'd like to add it to my galleries on Flickr.

Many thanks,
David (Passiflorae)