Passiflora, known also as the passion flowers or passion vines, is a genus of about 550 species of flowering plants, and the type genus of the family Passifloraceae. Passiflora species are widely cultivated for their striking flowers, flavorful fruits, traditional medicinal uses, and roles in dietary supplements and ayahuasca analogs, with several ornamental hybrids earning Royal Horticultural Society awards.
Description The genus mostly produces tendril-bearing vines, as well as some shrubs and trees. The plants can be woody or herbaceous. The flowers are regular and usually showy, with a distinctive corona. There can be as many as eight concentric coronal series, as in the case of P. xiikzodz. and P. alata. The hallmark of the genus is the androgynophore, a central column to which the stamens and pistil are attached, which can be very long in some species such as P. coactilis. The flower is pentamerous (except for a few Southeast Asian species) and ripens into an indehiscent fruit with numerous seeds. The fruit ranges from 5–20 centimetres (2–8 in) long and 2.5–5 cm (1–2 in) across, depending upon the species or cultivar.
Chemistry
Many Passiflora 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. actinia, 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.
Taxonomy
Passiflora is the most species-rich genus of both the family Passifloraceae and the tribe Passifloreae. With over 550 species, an extensive hierarchy of infrageneric ranks is required to represent the relationships of the species. The infrageneric classification of Passiflora not only uses the widely used ranks of subgenus, section and series, but also the rank of supersection. The New World species of Passiflora were first divided among 22 subgenera by Killip (1938) in the first monograph of the genus. More recent work has reduced these to 4, which are commonly accepted today (in order from most basal to most recently branching):
Astrophea (Americas, ~60 species), trees and shrubs with simple, unlobed leaves Passiflora (Americas, ~250 species), woody vines with large flowers and elaborate corolla Deidamioides (Americas, 13 species), woody or herbaceous vines Decaloba (Americas, Asia and Australasia, ~230 species), herbaceous vines with palmately veined leaves Some studies have shown that the segregate Old World genera Hollrungia and Tetrapathaea are nested within Passiflora, and form a fifth subgenus (Tetrapathaea). Other studies support the current four subgenus classification. Relationships below the subgenus level are not known with certainty and are an active area of research. 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 (three Australian species), Holrungiella (one New Guinean species) and Octandranthus (seventeen south and east Asian species). The remaining (New World) species of subgenus Decaloba are divided into seven supersections. Supersection Pterosperma includes four species from Central America and southern Mexico. Supersection Hahniopathanthus includes five species from Central America, Mexico and northernmost South America. Supersection Cicea includes nineteen species, with apetalous flowers. Supersection Bryonioides includes twenty-one species, with a distribution centered on Mexico. Supersection Auriculata includes eight species from South America, one of which is also found in Central America. Supersection Multiflora includes nineteen species. Supersection Decaloba includes 123 species.
Distribution Passiflora has a largely neotropic distribution, unlike other genera in the family Passifloraceae, which includes more Old World species (such as the genus Adenia). The vast majority of Passiflora are found in the United States and Latin America, although there are additional representatives in Southeast Asia and Oceania. New species continue to be identified: for example, P. xishuangbannaensis and P. pardifolia have only been known to the scientific community since 2005 and 2006, respectively. Some species of Passiflora have been naturalized beyond their native ranges. For example, the 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
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