Passiflora L.
Passiflora is a genus with more than 500 species with center of diversity in Central and South America. The highest species diversity is in Colombia (Ocampo & al. 2007, Ocampo & al. 2010, Ocampo & al. 2017). The genus is very popular in the horticultural trade although relatively few species are hardy enough for cultivation out-of-doors in western Europe. Jäger & al. (2008) only cite four species. In climatologically more favorable areas in Europe at least 30 species are grown as ornamentals (Miller 1997). Several species are also grown for their edible fruits, especially P. edulis. Two species of Passiflora have been recorded in the wild in Belgium.
Several websites are dedicated to the genus Passiflora, especially emphasizing on the cultivated species. Some of the more interesting are:
Passiflora Society International: http://www.passiflorasociety.org/
Passiflora Online: https://www.passionflow.co.uk/
Passiflora Gallery: http://www.floridanaturepictures.com/flowers/flowers.html
De Passifloratuin: https://www.passifloratuin.com/
The online journal Passiflora is entirely dedicated to the Passiflora genus. It is available at: https://www.passionflow.co.uk/passiflora-online-journal/.
1 Stipules semicircular, ca. 20 x 10 mm. Leaves usually with 5-7 deep lobes, dull above. Young stem usually angular === Passiflora caerulea
Stipules linear-lanceolate, ca. 10 mm long. Leaves 3-lobed to about middle, shiny above. Young stem usually terete === P. edulis
Literature
There is a vast literature on passion flowers. Only a selection of the more useful references is provided here under.
De Wilde W.J.J.O. (1974) The genera of tribe Passifloreae (Passifloraceae) with special reference to flower morphology. Blumea 22: 37–50. [available online at: http://repository.naturalis.nl/document/565501]
Feuillet C. & MacDougal J.M. (2003) A new infrageneric classification of Passiflora L. (Passifloraceae). Passiflora 13: 34–35, 37–38.
Frank A. & Kugler E. (2001) Hybrids and Culltiivars of Passion Flowers. A Checklist for the Genus Passiflora. 42 pp. [available online at: https://www.passionflow.co.uk/wp-content/uploads/2017/09/passiflora-hybr...
Goldman D.H. & MacDougal J.M. (2015) Passifloraceae. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 6. Oxford University Press, New York-Oxford: 170-182. [available online at: http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=10656]
Green P.S. (1971) Passiflora in Australasia and the Pacific. Kew Bull. 26: 539-558.
Hansen A.K., Gilbert L.E., Simpson B.B., Downie S.R., Cervi A.C. & Jansen R.K. (2006) Phylogenetic relationships and chromosome number evolution in Passiflora. Syst. Bot. 31: 138-150. [available online at: http://www.life.illinois.edu/downie/Passiflora.pdf]
Heenan P.B. & Sykes W.R. (2003) Passiflora (Passifloraceae) in New Zealand: a revised key with notes on distribution. New Zealand J. Bot. 41(2): 217-221. [available online at: http://www.tandfonline.com/doi/pdf/10.1080/0028825X.2003.9512842]
Jäger E.J., Ebel F., Hanelt P. & Müller G. (eds.) (2008) Rothmaler Band 5. Exkursionsflora von Deutschland. Krautige Zier- und Nutzpflanzen. Springer Verlag, Berlin: 880 p.
Killip E. P. (1938) The American Species of Passifloraceae. Publ. Field Mus. Nat. Hist., Bot. Ser. 19. [available online at: https://www.biodiversitylibrary.org/bibliography/2269#/summary]
Lawrence G.H.M. (1960) Identification of the cultivated Passionflowers. Baileya 8: 121-132.
Marsh A.S. (2001) Karyology and cytotaxonomy of the genus Passiflora L. (Passifloraceae). Pl. Syst. Evol. 226: 69-84.
Miller D.M. (1997) Passiflora. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 5. Cambridge University Press, Cambridge: 258-262.
Muschner V.C., Lorenz A.P., Cervi A.C., Bonatto S.L., Souza-Chies T.T., Salzano F.M. & Freitas L.B. (2003) A first molecular phylogenetic analysis of Passiflora (Passifloraceae). Am. J. Bot. 90(8): 1229-1238. [available online at: https://www.ncbi.nlm.nih.gov/pubmed/21659223]
Muschner V.C., Zamberlan P.M., Bonatto S.L. & Freitas L.B. (2012) Phylogeny, biogeography and divergence times in Passiflora (Passifloraceae). Genet. Mol. Biol. 35(4 Suppl): 1036-1043. [available online at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3571420/]
Ocampo J., Coppens D´Eeckenbrugge G. & Jarvis A. (2010) Distribution of the genus Passiflora L. diversity in Colombia and its potential as an indicator for biodiversity management in the Coffee Growing Zone. Diversity 2(11): 1158-1180. [available online at: https://agritrop.cirad.fr/558473/1/document_558473.pdf]
Ocampo J., Coppens D'Eeckenbrugge G. & Morales G. (2017) Genetic resources of colombian Tacsonias (Passiflora supersection Tacsonia): A biological treasure still to discover, use and conserve. Passiflora Online Journal 10: 24-53. [available online at: http://agritrop.cirad.fr/585137/]
Ocampo J., Coppens D.G., Restrepo M., Jarvis A., SalazarM. & Caetano C. (2007) Diversity of Colombia Passifloraceae: biogeography and an updated list for conservation. Biota Colombiana 8: 1-45. [available online at: http://publications.cirad.fr/une_notice.php?dk=549361]
Rejmánek M. (2009) Passiflora (Passifloraceae) in California: a key and comments on naturalized species. Botanical Electronic News 406, available online at: http://www.ou.edu/cas/botany-micro/ben/ben406.html.
Rome M. & Coppens d’Eekenbrugge G. (2018) Taxonomie et évolution dans le genre Passiflora: synthèse des connaissances actuelles. Bull. mens. Soc. linn. Lyon 87(5-6): 121-136. [available online at: https://www.researchgate.net/publication/324830880_Taxonomie_et_evolutio...
Shiamala Devi Ramaiya, Japar Sidik Bujang, and Muta Harah Zakaria (2014) Genetic Diversity in Passiflora Species Assessed by Morphological and ITS Sequence Analysis. The Scientific World Journal Article ID 598313, 11 pages. doi:10.1155/2014/598313 [available online at: https://www.hindawi.com/journals/tswj/2014/598313/cta/]
Ulmer T. & MacDougal J.M. (2004) Passiflora: Passionflowers of the World, Timber Press, Portland, Ore, USA.
Vanderplank J. (2000) Passion Flowers. Ed. 3. Cambridge, Mass.
Young B.R. (1970) Identification of passionflowers in New Zealand (Dicotyledones: Passifloraceae). Records of the Auckland Institute and Museum 7: 143-169.