Passiflora caerulea L. (S Am.) – A rare and probably always ephemeral escape from cultivation. First recorded in 2005 on a basement wall in the city of Antwerp. Since then regularly recorded in similar (i.e. urban) circumstances elsewhere in Antwerp and Ghent. All plants are young, obviously self-sown individuals growing in the vicinity of planted, fruiting mother plants. Rather exceptionally it is also seen outside urban areas and then probably as mere relics of former cultivation (e.g. in Wachtebeke in 2017). Also seen on ground heaps in the Zeebrugge port area in 2014.
Similar records of Passiflora caerulea are available for instance from the British Isles (Clement 1982, Clement & Foster 1994). It is sometimes considered an undesirable weed, for instance in California (DiTomaso & Healy 2007). Even in the absence of sexual reproduction, this species can persist and even spread locally by root suckering (Goldman & MacDougal 2015).
Passiflora caerulea is one of the few species of the genus that is fully hardy in Belgium. It is quite variable and numerous cultivars and hybrids are offered in the horticultural trade. All, however, are readily distinguished by the semi-circular, very conspicuous stipules.
Selected literature
Clement E.J. (1982) Adventive news 23. BSBI News 32: 18-20. [available online at: http://archive.bsbi.org.uk/BSBINews32.pdf]
Clement E.J. & Foster M.C. (1994) Alien plants of the British Isles. BSBI, London: XVIII + 590 p.
DiTomaso J.M. & Healy E.A. (2007) Weeds of California and Other Western States. University of California.
Garcia M.T.A. & Hoc P.S. (1998) Floral biology and reproductive system of Passiflora caerulea (Passifloraceae). Beitr. Biol. Pfl. 70(1): 1-20.
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]
Keighery G.J. (1981) Passiflora caerulea in Western Australia. West. Austral. Herb. Res. Notes 5: 136.
MacDougal J.M. (1989) The correct name for the hybrid Passiflora alata x P. caerulea (Passifloraceae). Baileya 23(2): 68-73.