Can somebody identify this flowering plant? Recently found in a garden in England, but it is said to be spreading spontaneously. Possibly a Rubiaceae. I only got this picture to rely on. Seems to be quite a mystery. Thanks for your interest! Hans
On the Encyclopedia of Life website (www.eol.org) you can see pictures of Asperula taurina having white flowers with a hint of lilac, as well as white-white flowers. Soil conditions and mutations can play a role in changing flower colour and of course man can select for lilac cultivars. It is is not clear if any hybridisation could be involved in this "lilac Asperula taurina." Anyway, Asperula taurina is probably the best reply to my question. So thank you again, Franz Starlinger, Narayanan Nair Mohanan and Carmelo Maria Musarella.
The colour of the flowers is the point, why I was not sure with Asperula taurina. In the meantime I have found out that there exists Asperula taurina subsp. caucasica (= Asperula caucasica Pobed.). The protologue of this taxon (http://biodiversitylibrary.org/page/29988127 ) describes the flowers as "corolla alba raro rosea". So, it would not have been difficult to select licac flowers for horticulture.