Floral polymorphism in common primrose (Primula vulgaris Huds., Primulaceae) of the Northeastern Black Sea coast

The common primrose (Primula vulgaris, Primulaceae) has several color morphs. Two of them, traditionally treated as subspecies, vulgaris with white and yellow flowers, and polymorphic sibthorpii with the predominance of dark (anthocyanin-containing) flowers, often occur at the same places along the eastern Black Sea coast, stretching over 250?km between Novorossiysk and Pitsunda. Seventy-one primrose populations were sampled on almost every 10-km interval of this line. We found a significant trend of increase in the proportion of dark flowers in the populations from northwest to southeast, with an abrupt (60?km) transitional zone. Within this zone, we found significant spatial trends correlated with altitude and distance from seashore. No reliable morphological differences between color forms were found. The observed large-scale geographical structure may be a joint result of the recent contact of previously isolated color morphs, heterogeneity of pollinator preferences, and genetic drift.