Is genetic diversity congruent with morphological diversity across the distributional range of the Melampyrum subalpinum group (Orobanchaceae)?

• Allozyme variation of 27 Melampyrum subalpinum group populations was evaluated.
• Genetical and morphological variation of M. subalpinum group are congruent.
• The allelic richness is higher in central than in marginal populations.
• Allelic enrichment was observed in supposedly hybrid populations.
• Recently there is a limited gene flow between the populations.

The Melampyrum subalpinum group consists of morphologically diverse populations traditionally treated as closely related taxa with patchy distribution limited to Central Europe. The centre of the morphological variability and geographical distribution of the group lies on the north-eastern edge of the Alps in the Vienna Forest, while marginal, morphologically uniform populations occur in the Czech Republic and Slovakia. Genetic variation and population structure within the distribution range of the group remains unknown; we hypothesise that the marginal population are genetically depauperate. Allozymes were used to assess the genetic structure of 27 populations present throughout the distribution area; four Melampyrum nemorosum populations from the Vienna Forest were also analysed because of the presumed hybridization. An artificial pollination experiment was carried out to examine the possibility of autogamy. Four enzyme systems were clearly resolved and scored for one polymorphic locus each with a total of 20 alleles.Seven out of 49 flowers with preserved stamens developed seeds after self-pollination. Genetic variation was generally congruent with the known pattern of the morphological variation of the group. The allelic richness was higher in the Austrian populations than in marginal Czech and Slovak populations. Some wide-leaved populations from the Vienna Forest had a rather high number of alleles which may be caused by allelic enrichment due to former hybridization with M. nemorosum. Czech and Slovak populations are genetically derived from Austrian populations. The high differentiation among populations suggests that the current gene flow between populations is limited. The high inbreeding coefficient in some populations indicates that there is a certain level of selfing within the populations. The pollination experiment does not contradict the possibility of autogamy. In general, our data are congruent with the central-marginal model with more variable Austrian populations and less variable isolated and probably partly inbreeding Czech and Slovak populations.