Evolution of the hawthorns (Crataegus, Rosaceae) of Central Europe

Abstract

Hawthorn species of Crataegus L. subg. Crataegus sect. Crataegus ser. Crataegus (Rosaceae) are abundant shrubs in European scrub, hedges, and forest margins, yet the taxonomy of these plants said-to-be hybridizing freely is only based on morphological traits. To investigate the relationship of the Central European hawthorn species (i.e. C. laevigata (POIR.) DC., Crataegus monogyna JACQ., C. rhipidophylla GAND. s. l. = C. rhipidophylla GAND. s. str. and C. lindmanii HRABĚTOVÁ, C. ×macrocarpa HEGETSCHW. s. l. = C. ×macrocarpa HEGETSCHW. s. str. and C. ×calycina PETERM., C. ×media BECHST., C. ×subsphaerica GAND. s. l. = C. ×subsphaerica GAND. s. str. and C. ×domicensis HRABĚTOVÁ) a suite of handed down and novel morphological traits (morphology of leaves, flowers, and fruits) was assessed and compared to their genetic constitution for the first time in this study. Genetic analyses based on seven unlinked SSR markers of two linkage groups. In addition breeding experiments were performed to gather insight in the reproductive behaviour. The results of the present study do not provide better resolution of morphotaxa with an increased number of traits analysed. Instead, a small subset of the handed down traits was confirmed sufficient to sift out the groups of the inherited speciation model of Central European haws. Three extreme and concordant morphological and genetic phenotypes among the considered taxa with smooth transition stages between them can be reported. There is high level of morphological but also genetic diversity within all of the Crataegus species. Although they share a lot of alleles there are also private alleles for species and groups, respectively. In total the level of genetic differentiation is moderate. No final conclusion whether the considered species reproduce facultatively or mandatorily sexually or apomictically can be drawn from the breeding experiments. Further investigations in pseudogamous apomixis with sterilised pollen and the analysis especially of developing seeds with flow cytometric measurement is required. Yet, the results grant more insight in the reproductive modes of Central European hawthorns.