Hybrids between Rubus caesius and Rubus sect. Corylifolii (Rosaceae) and their relation to R. cyclomorphus, R. tiliaster, R. glauciformis, R. slesvicensis and R. firmus

Abstract

Using flow cytometry and microsatellite DNA analysis (MSDA), we studied hybrids between Rubus caesius and various other Rubus species, with an emphasis on Sweden. We show that hybrids between Rubus caesius and Rubus sect. Corylifolii arise easily. They show a large variation in morphology, but can normally be recognised by a number of characters. They are typically hexaploids, but ~13% of the hybrids are pentaploids and ~8% tetraploids. With MSDA, they are harder to identify than hybrids with R. idaeus, partly because all Corylifolii species have themselves arisen from R. caesius hybrids and therefore share many alleles with R. caesius, partly because hybridisation with R. caesius seems to give rise to some variation in microsatellite regions. Hybrids with species of R. sect. Rubus are much rarer in Sweden and we have only identified one such case. We show that R. cyclomorphus and R. tiliaster are not proper apomictic species, at least not in Sweden, but rather a collection of genetically unrelated hybrids between R. caesius and R. raduloides or R. camptostachys. MSDA analysis of R. slesvicensis and R. firmus shows that these species are problematic. We identify two distinct taxa, one from Skåne in Sweden, which we describe as a new species, R. ruboculus and another from the neighbourhood of Viborg and Schleswig, although the latter is probably not identical with R. slesvicensis s.s. All the other samples form a diverse group of putative R. caesius hybrids at three different ploidy levels. Rubus glauciformis is uniform in Småland, Öland and Blekinge, but becomes harder to distinguish from various hybrids in Skåne. We conclude that once R. caesius and R. idaeus hybrids are properly identified, along with a small number of new apomictic species (often with a local distribution), the genus Rubus does not pose any serious taxonomical problems in Sweden.