Campanula portenschlagiana and Campanula poscharskyana.
by John Grace, the University of Edinburgh
At this time of year the garden walls in many of our towns and cities are adorned with blue bellflowers. Some people love these uninvited guests, others consider them to be weeds and pull them out. There are two main species, both evergreen perennials, Campanula portenschlagiana (the Dalmatian or Adria Bellflower) and Campanula poscharskyana (the Trailing Bellflower). The Latin names are hard to remember and even harder to spell. I’ve started calling them port and posh.
They are superficially similar but the corolla tube of poscharskyana is more deeply cut and so the petals are much more spreading, star-like from above. Stace says ‘lobed ½ to ¾ way to base’ to make a broadly bell-shaped flower. From a distance, these flowers are rather grey-blue. In contrast, C. portenschlagiana is purple-blue or violet, and has a funnel-shaped corolla which is lobed less than half-way to base. They differ in hairiness: C. poscharskyana has grey-hairy stems whilst C. portenschlagiana’s stems are practically glabrous. Their growth forms are different: portenschlagiana is mound-forming, poscharskyana is trailing. Confused? Then look at the pictures and note that the leaves are also different.
When did they get here? My trusty 1981 edition of Clapham Tutin and Warburg’s Excursion Flora doesn’t give them a mention. Harrap (2013) says poscharskyana was introduced to the UK in 1931 and first recorded in the wild in 1957. The rapid spread since then is evident in BSBI data (see the table). There is however something distinctly strange about these data. The records (hectads occupied) of the two species are highly correlated (r = 0.99, p = <0.01), suggesting that either they have identical habitat requirements and dispersal rates or that recorders have confused them.
|Dates||Hectads With posh||Hectads with port|
Are they invasive? They are never far from gardens, cemeteries and parks, and almost always they are associated with walls. They are not invasive so far, and if they show signs of taking over the whole street they can easily be pulled out. However, they may be resistant to herbicides: I have seen poscharskyana surviving an onslaught by Council workers whilst nearby species were killed. They are ignored by the hungry snails that share their wall. Their resistance to gasteropod grazing may be related to latex: both species are latex-producers; based on a small sample from my garden, posh has more of it than port.
In the UK and North America they are sold in garden centres and named varieties are available. My google search found many US patents for special forms of both species, suggesting that some people think these are commercially useful. Indeed, both are rated as possible food plants in https://pfaf.org/user/DatabaseSearhResult.aspx?LatinName=C%25. I’m not sure how this would work – perhaps green-leaf salad and blue flowers for pretty ice cubes? One authority, wildfooduk, states ‘Very mild. Leaves are slightly refreshing’, but warns that they are often growing in the ‘dog-pee zone’, so be careful. Indeed.
Acknowledgements (i) I thank the BSBI for giving permission to use their distribution maps and for kind advice (ii) The blogger bugwomanlondon was very helpful and I would like strongly to recommend her site: https://bugwomanlondon.com/2014/10/22/wednesday-weed-trailing-bellflower/
Clapham AR, Tutin TG & Warburg EF (1981) Excursion Flora of the British Isles. Cambridge.
Harrap S (2013) Harrap’s Wildflowers. Bloomsbury.
Kovačić S (2004) The genus Campanula L. (Campanulaceae) in Croatia, circum-Adriatic and west Balkan region Acta Bot. Croat. 63 (2), 171–202.
Stace C (2019) New Flora of the British Isles 4th edition C&M Floristics.
Tutin TG et al. (1976) Flora Europaea, Vol. 4 Plantaginaceae to Compositae. Cambridge University Press.