Veronica opaca in Mitteleuropa - Erkennungsmerkmale, Verbreitung und standörtliches Verhalten

Abstract

Until now it has not been possible to make reliable statements about the general area of distribution and ecological character of Veronica opaca Fries because the basic requirement for this - a correct identification - was frequently not available. To facilitate correct identification, important distinguishing characteristics, along with differences to closely related species (the Veronica agrestis -group) as well as to other Veronica weed-species, are presented and illustrated with drawings. The basis for a distribution map is provided from more than 50 Central European herbaria, as well as critically selected literature and our own observations. According to these sources, the center of distribution lies in the medium-altitude, mountainous area between the Eifel and the Carpathians. The range stretches from the Netherlands eastward to Russia, and from Austria north to Sweden. For a weed, this is an unusually tightly limited range - all the more remarkable, since V. opaca has good expansion potential, just like V. persica and V. polita, which are now distributed worldwide. Until now this limitation can only be explained with special climatic and soil requirements. Vegetation releves and more detailed information about habitat behaviour make it possible to recognize that V. opaca takes an intermediate position between V. agrestis and V. polita regarding its soil and climatic preferences. Preferred growth sites are vegetable gardens, as well as fields of root crops. With the intensification of agriculture, V. opaca has disappeared as a weed of cultivated fields in many locations and has become exclusively a garden weed. The distribution map still has many gaps. Therefore, we are very interested in receiving further herbarial specimens.