In Campanulas, the betulifolia group consists of the species betulifolia, trogerae, choruhensis, seraglio, and kirpicznikovii. All have been described relatively recently, betulifolia by the middle of the last century, and choruhensis only in 1993. They come from the the region between the Black and Caspian Seas in the Caucasus Mountains and further south into eastern Turkey, occupying cracks and crevices in limestone or volcanic rock.
In general, the plants form tufts of more-or-less birch-like leaves from which they send decumbent or ascending stems about 10-20 cm long, which are brittle in some species. They flower in spring to early summer and go dormant in fall, looking brown and dead in the open but retaining some green in the greenhouse. All are recommended for raised beds, troughs or walls, and they do well in crevices or pots, as their branches, whether they start out lax or ascending, tend to sag under the weight of the flowers. They prefer a limy to neutral soil, generally well-drained. All need their seed to go through a cold period (stratification) and exposure to light to germinate, so seed should be sown on the surface of the growing medium.
Betulifolia has the widest range of the group, from the Caucasus down through Armenia into Turkey. It likes sun and a drier crevice or scree than some of the others, and perhaps a bit more alkaline. It has pale pink or white tubular-campanulate flowers, but buds that are described as wine red, (although the plant in the photo above does not show this).
Choruhensis is from Turkey, where Nicholls reports it likes cool northern exposures, and another source recommends a gravelly humus soil with a pH tending towards neutral. The bud is ribbed, rose pink (shown well in this photo; be sure to click on it to enlarge it), and the goblet-shaped flower is ivory with a hint of pink, or in some forms a strong pink.
Kirpicznikovii is the northernmost member of the group, from the Russian/Georgian Caucasus, and is the only one not to have pink tendencies. It occupies sunny limestone crevices and has yellowish buds and large creamy flowers.
Trogerae is from eastern Turkey, growing in part shade in poor alkaline soil, but with some humus. Ribbed white or pale pink buds open to large pure white, almost flat stars.
Seraglio, also from Turkey, sounds from the published description to be very similar to trogerae, a wide-open, stellate bloom. It might prefer more sun and a leaner soil. Its name, it seems likely, is a corruption of the place-name Sarigol in Turkey where it's found, rather than a reference to seraglio as a Turkish harem or palace.
Also available commercially is a hybrid between betulifolia and trogerae which is reported to be easier than either. In 1990 this cross was made and a selected seedling was named "Edward Forrest". Clones of this hybrid are still sold, however several nurseries have made their own crosses and are marketing the results simply as "betulifolia x trogerae".
Created by Hannah.
The original document is available at http://nargs.org/nargswiki/tiki-index.php?page=betulifolia+group