Data from: Multiple independent origins of intermediate species between Sorbus aucuparia and S. hybrida (Rosaceae) in the Baltic region

Populations intermediate between the diploid and sexual Sorbus aucuparia
and the tetraploid and facultative apomictic Sorbus hybrida are scattered
in coastal regions of southern Scandinavia. Our aims were to investigate
whether these populations were of local and independent origins, whether
they were morphologically and molecularly distinct from each other and
whether they could give rise to constant offspring by apomixis. Six
intermediate populations from the Baltic Sea basin were studied for
variation at nuclear and plastid microsatellite loci, for morphological
differentiation patterns, and for ploidy level by flow cytometry. Seeds
were sown to check for constancy with the mother plants. Three populations
from Gotland and possibly the small population from Uppland were in each
case fixed for a unique combination of genetic markers, had restricted
variation in leaf shape and were morphologically divergent from each
other. Flow cytometry analysis showed that the four genetically
monomorphic populations were consistently triploid. Cultivation showed
that offspring from trees within two of the monomorphic populations had
leaf shapes closely similar to the mother individuals. In contrast, a
population from Gotland and a population from Åland were variable at
molecular marker loci and were variable in leaf shape. The three
monomorphic Gotland populations and possibly also the Uppland population
propagate asexually by apomixis, and they have independent origins. The
two variable populations are apparently composed of hybrids that have been
formed repeatedly and independently between individuals of the two
parental species growing at the same sites. One of the Gotland apomicts
has already been described as Sorbus teodori. Sorbus faohraei Hedrén
& J.Levin and Sorbus atrata Hedrén & J.Levin are described
as new apomictic species from Gotland.