Passiflora

Distribution

The family Passifloraceae has a pantropical distribution. Passiflora itself is absent from Africa, where many other members of the family Passifloraceae occur (e.g. the more plesiomorphic Adenia).

Most species are found in South America, eastern Asia, southern Asia and New Guinea. Nine separate species of Passiflora are native to the United States, found from Ohio to the north, west to California and south to the Florida Keys. Four or more species are also found in Australia and a single endemic species in New Zealand. New species continue to be identified: for example, P. pardifolia and P. xishuangbannaensis have only been known to the scientific community since 2006 and 2005, respectively.

Some species of Passiflora have been naturalised beyond their native ranges. For example, blue passion flower (P. caerulea) now grows wild in Spain. The purple passionfruit (P. edulis) and its yellow relative flavicarpa have been introduced in many tropical regions as commercial crops.

Ecology

The passion flowers have a unique structure, which in most cases requires a large bee to effectively pollinate. In the American tropics, wooden beams are mounted very near passionfruit plantings to encourage carpenter bees to nest. The size and structure of flowers of other Passiflora species is optimized for pollination by hummingbirds (especially hermits like Phaethornis), bumble bees, Carpenter bees (Xylocopa varipuncta), wasps or bats, while others are self-pollinating. The sword-billed hummingbird (Ensifera ensifera) with its immensely elongated bill has co-evolved with certain passion flowers, such as P. mixta.

Yellow passion flower (P. lutea) pollen is apparently the only pollen eaten by the unusual bee Anthemurgus passiflorae. However, these bees simply collect the pollen, but do not pollinate the flowers.

The leaves are used as food plants by the larva of a number of Lepidoptera. To prevent the butterflies from laying too many eggs on any single plant, some passion flowers bear small colored nubs which resemble the butterflies' eggs and seem to fool them into believing that more eggs have already been deposited on a plant than actually is the case. Also, many Passiflora species produce sweet nutrient-rich liquid from glands on their leaf stems. These fluids attract ants which will kill and eat many pests that they happen to find feeding on the passion flowers. The following lepidoptera larvae are known to feed on Passiflora:

The bracts of the stinking passion flower are covered by hairs which exude a sticky fluid. Many small insects get stuck to this and get digested to nutrient-rich goo by proteases and acid phosphatases. Since the insects usually killed are rarely major pests, this passion flower seems to be a protocarnivorous plant.

Banana passion flower or "banana poka" (P. tarminiana), originally from Central Brazil, is an invasive weed, especially on the islands of Hawaii. It is commonly spread by feral pigs eating the fruits. It overgrows and smothers stands of endemic vegetation, mainly on roadsides. Blue passion flower (P. caerulea) is holding its own in Spain these days, and it probably needs to be watched so that unwanted spreading can be curtailed.

On the other hand, some species are endangered due to unsustainable logging and other forms of habitat destruction. For example, the Chilean passion flower (P. pinnatistipula) is a rare vine growing in the Andes from Venezuela to Chile between 2,500 and 3,800 meters altitude, and in Coastal Central Chile, where it occurs in woody Chilean Mediterranean forests. P. pinnatistipula has a round fruit, unusual in Tacsonia group species like banana passion flower and P. mixta, with their elongated tubes and brightly red to rose-colored petals.

Notable and sometimes economically significant pathogens of Passiflora are several sac fungi of the genus Septoria (including S. passiflorae), the undescribed proteobacterium called "Pseudomonas tomato" (pv. passiflorae), the Potyvirus passionfruit woodiness virus, and the Carlavirus Passiflora latent virus.

Use by humans

A number of species of Passiflora are cultivated outside their natural range for their beautiful flowers and delicious fruit. Hundreds of hybrids have been named; hybridizing is currently being done extensively for flowers, foliage and fruit. The following hybrids and cultivars have gained the Royal Horticultural Society's Award of Garden Merit:-

During the Victorian era the flower (which in all but a few species lasts only one day) was very popular, and many hybrids were created using the winged-stem passion flower (P. alata), the blue passion flower (P. caerulea) and other tropical species.

Many cool-growing Passiflora from the Andes Mountains can be grown successfully for their beautiful flowers and fruit in cooler Mediterranean climates, such as the Monterey Bay and San Francisco in California and along the western coast of the U.S. into Canada. One blue passion flower or hybrid even grew to large size at Malmö Central Station in Sweden.

Passion flowers have been a subject of studies investigating extranuclear inheritance; paternal inheritance of chloroplast DNA has been documented in this genus. The plastome of the two-flowered passion flower (P. biflora) has been sequenced.

The French name for this plant has lent itself to L. Famille Passiflore, a highly successful children's book series by Geneviève Huriet, and an animated series based upon it. These have been translated into English as Beechwood Bunny Tales and The Bellflower Bunnies.

Fruit

Most species have round or elongated edible fruit from two to eight inches long and an inch to two inches across, depending upon the species or cultivar.

Traditional medicine

P. incarnata (maypop) leaves and roots have a long history of use among Native Americans in North America and were adapted by the European colonists. The fresh or dried leaves of maypop are used to make a tea that is used for insomnia, hysteria, and epilepsy, and is also valued for its analgesic properties. P. edulis (passion fruit) and a few other species are used in Central and South America for similar purposes. Once dried, the leaves can also be smoked.

The medical utility of only a few species of Passiflora has been scientifically studied. In initial study in 2001 for treatment of generalized anxiety disorder, maypop extract performed as well as oxazepam but with fewer short-term side effects. It was recommended to follow up with long-term studies to confirm these results.

A study performed on mice demonstrated that Passiflora alata has a genotoxic effect on cells, and suggested further research was recommended before this one species is considered safe for human consumption.

Passionflower herb (Passiflorae herba) from P. incarnata is listed in the European Pharmacopoeia. The herbal drug should contain not less than 1.5% total flavonoids expressed as vitexin.

Passionflower is reputed to have sedative effects and has been used in sedative products in Europe, but in 1978, the U.S. Food and Drug Administration prohibited its use in over-the-counter sedative preparations because it had not been proven safe and effective. In 2011, the University of Maryland Medical Center reported that passionflower "... can trigger side effects and can interact with other herbs, supplements, or medications. For these reasons, you should take herbs with care, under the supervision of a health care provider."

Passionflower is classified as generally recognized as safe (GRAS) for use in foods in the US, and is “possibly safe when used orally and appropriately for short-term medicinal purposes,” “possibly unsafe when used in excessive amounts,” but unsafe when used orally during pregnancy since “...passionflower constituents show evidence of uterine stimulation.” The database suggests it is possibly effective for adjustment disorder with anxious mood, anxiety, and opiate withdrawal, but it “can cause dizziness, confusion, sedation, and ataxia” and there are some reports of more severe side effects including vasculitis and altered consciousness.

Chemistry

Many species have been found to contain beta-carboline harmala alkaloids, some of which are MAO inhibitors. The flower and fruit have only traces of these chemicals, but the leaves and the roots often contain more. The most common of these alkaloids is harman, but harmaline, harmalol, harmine, and harmol are also present. The species known to bear such alkaloids include: P. actinea, P. alata (winged-stem passion flower), P. alba, P. bryonioides (cupped passion flower), P. caerulea (blue passion flower), P. capsularis, P. decaisneana, P. edulis (passion fruit), P. eichleriana, P. foetida (stinking passion flower), P. incarnata (maypop), P. quadrangularis (giant granadilla), P. suberosa, P. subpeltata and P. warmingii.

Other compounds found in passion flowers are coumarins (e.g. scopoletin and umbelliferone), maltol, phytosterols (e.g. lutenin) and cyanogenic glycosides (e.g. gynocardin) which render some species, i.e. P. adenopoda, somewhat poisonous. Many flavonoids and their glycosides have been found in Passiflora, including apigenin, benzoflavone, homoorientin, 7-isoorientin, isoshaftoside, isovitexin (or saponaretin), kaempferol, lucenin, luteolin, n-orientin, passiflorine (named after the genus), quercetin, rutin, saponarin, shaftoside, vicenin and vitexin. Maypop, blue passion flower (P. caerulea), and perhaps others contain the flavone Chrysin. Also documented to occur at least in some Passiflora in quantity are the hydrocarbon nonacosane and the anthocyanidin pelargonidin-3-diglycoside.

The genus is rich in organic acids including formic, butyric, linoleic, linolenic, malic, myristic, oleic and palmitic acids as well as phenolic compounds, and the amino acid α-alanine. Esters like ethyl butyrate, ethyl caproate, n-hexyl butyrate and n-hexyl caproate give the fruits their flavor and appetizing smell. Sugars, contained mainly in the fruit, are most significantly d-fructose, d-glucose and raffinose. Among enzymes, Passiflora was found to be rich in catalase, pectin methylesterase and phenolase.

Etymology and names

The "Passion" in "passion flower" refers to the passion of Jesus in Christian theology. In the 15th and 16th centuries, Spanish Christian missionaries adopted the unique physical structures of this plant, particularly the numbers of its various flower parts, as symbols of the last days of Jesus and especially his crucifixion:

The flower has been given names related to this symbolism throughout Europe since that time. In Spain, it is known as espina de Cristo ("thorn of Christ'"). Older Germanic names include Christus-Krone ("Christ's crown"), Christus-Strauss ("Christ's bouquet"), Dorn-Krone ("crown of thorns"), Jesus-Lijden ("Jesus' passion"), Marter ("passion") or Muttergottes-Stern ("Mother of God's star").

Outside the Christian heartland, the regularly shaped flowers have reminded people of the face of a clock. In Israel they are known as "clock-flower" (שעונית) and in Greece as "clock plant" (ρολογιά); in Japan too, they are known as tokeisō (時計草, "clock plant"). In Hawaiian, they are called lilikoʻi; lī is a string used for tying fabric together, such as a shoelace, and liko means "to spring forth leaves".

In India, blue passionflowers are called Krishnakamala in Karnataka and Maharashtra, while in Uttar Pradesh and generally north it is colloquially called "Paanch Paandav" (referring to the five Pandavas in the Hindu epic, the Mahabharata). The five anthers are interpreted as the five Pandavas, the divine Krishna is at the centre, and the radial filaments are opposing hundred. The colour blue is moreover associated with Krishna as the colour of his aura.

In northern Peru and Bolivia, the banana passionfruits are known as tumbos. This is one possible source of the name of the Tumbes region of Peru.

In Turkey, the shape of the flowers have reminded people of Rota Fortunae, thus it called Çarkıfelek.

Taxonomy

Passiflora stands as the genus with the highest number of species within both the Passifloraceae family and the Passifloreae tribe. Hosting more than 530 species, this genus necessitates a detailed classification system to accurately depict the relationships among its diverse species. To manage this complexity, the classification within Passiflora extends beyond the commonly utilized subgenus, section, and series categories, incorporating an additional category known as supersection to better organize and understand the vast number of species.

The New World species of Passiflora were divided among 22 subgenera by Killip (1938). More recent work reduces these to 4 - Astrophea (Americas, 57 species), Deidamioides (Americas, 17 species), Passiflora (Americas, >200 species) and Decaloba (Americas, Asia and Australasia, >200 species). Other studies have shown that the segregate Old World genera Hollrungia and Tetrapathaea are nested within Passiflora, and form a fifth subgenus (Tetrapathaea).

The Old World species form two clades - supersection Disemma (part of subgenus Decaloba) and subgenus Tetrapathaea. The former is composed of 21 species divided into sections Disemma (3 Australian species), Holrungiella (1 New Guinean species) and Octandranthus (17 south and east Asian species).

The remaining (New World) species of subgenus Decaloba are divided into 7 supersections. Supersection Pterosperma includes 4 species from Central America and southern Mexico. Supersection Hahniopathanthus includes 5 species from Central America, Mexico and northernmost South America. Supersection Cicea includes 19 species, with apetalous flowers. Supersection Bryonioides includes 21 species, with a distribution centered on Mexico. Supersection Auriculata includes 8 species from South America, one of which is also found in Central America. Supersection Multiflora includes 19 species. Supersection Decaloba includes 123 species.