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This study focuses on the frequency of reproductive modes and the role of reproductive mode variation in diversification of the genus Sorbus s.l. and evolutionary success of individual taxa. Our sampling covers all four ploidies known in Sorbus and includes stabilized taxa and recently formed biotypes. We infer reproductive modes of 3660 seeds using the flow cytometric seed screen method; we also calculated ploidy of contributing pollen. Sorbus shows high variability in reproduction pathways (sexuality, apomixis, formation of BIII hybrids, haploid parthenogenesis). Diploids are sexual, whereas polyploids show predominantly pseudogamous apomixis. In half of the polyploids studied, several reproductive modes were present and even intra-individual variation was detected. Diploids, tetraploids and pentaploids are pollinated by conspecific pollen, whereas triploids are largely, but not fully, dependent on the pollen of other species. In pseudogamous seeds, fertilization of the central cell by both sperms is a dominant pathway of endosperm origin. Flow cytometry of pollen did not detect unreduced pollen at any ploidy. The principal mechanisms of diversification in Sorbus are residual sexuality in apomicts, production of triploid taxa from diploid–tetraploid crosses and production of BIII hybrids. Evolutionary success of Sorbus taxa is largely dependent on the breeding system and is determined by self-(in)compatibility and the interplay between stabilizing apomixis and variation-generating sexuality.

In plants, apomixis results in the production of clonal offspring via seed and can provide reproductive assurance for isolated individuals. However, many apomicts require pollination to develop functional endosperm for successful seed set (pseudogamy) and therefore risk pollination-limitation, particularly in self-incompatible species that require heterospecific pollen. We used microsatellite paternity analysis and hand pollinations to investigate pollen-limitation in Sorbus subcuneata, a threatened endemic tree that co-occurs with its congener, S. admonitor. We confirmed that S. subcuneata is an obligate pseudogamous apomict, but open-pollinated flowers rarely produced seed (flower-to-seed conversion

Background: Pollen stainability is often used in hybridisation studies as a proxy for true pollen viability. Its value for assessing fertility and ploidy level was assessed in British Sorbus L. Aims: To assess variation in pollen stainability within and between Sorbus taxa, and its relationship to ploidy level. Methods: Stainability of pollen was examined in herbarium specimens using Alexander's Stain. Results: The diploid species (S. aria, S. aucuparia, S. torminalis) have the highest pollen stainability, followed by tetraploids (S. croceocarpa, S. devoniensis, S. eminens, S. intermedia, S. lancastriensis, S. latifolia, S. leptophylla, S. pseudofennica, S. rupicola). The diploid hybrids (S. × thuringiaca, S. × vagensis) have lower stainability than their parents. Triploids (S. arranensis, S. bristoliensis, S. decipiens, S. leyana, S. minima, S. pseudomeinichii, S. whiteana, S. wilmottiana) usually have the lowest stainability. Conclusions: There is significant variation between taxa within each group, so...

The parentage of polyploid Sorbus species in the British Isles was investigated using plastid DNA microsatellites. Four hundred and fifty-three samples from 30 taxa were screened using six microsatellite fragments, which gave 28 haplotypes. The haplotypes formed groups clearly related to the ancestral diploids Sorbus aria, Sorbus aucuparia, and Sorbus torminalis. Species in the Sorbus aria group all had Aria haplotypes (with the exception of one English S. aria), species in the Sorbus anglica group had an Aucuparia haplotype, and species in the Sorbus latifolia group had a Torminalis haplotype. Sorbus intermedia had an Aucuparia haplotype. This indicated that the hybridization events that led to the formation of species in the S. anglica and S. latifolia groups usually did so with S. aria s.l. as the pollen-donating (paternal) parent. The polyploids S. anglica, Sorbus bristoliensis, Sorbus croceocarpa, Sorbus decipiens, Sorbus devoniensis, Sorbus hibernica, Sorbus lancastriensis, Sorbus leptophylla, Sorbus leyana, Sorbus minima, Sorbus rupicola, Sorbus subcuneata, Sorbus vexans, Sorbus whiteana, Sorbus wilmottiana, and three unnamed taxa may each be derived from a single maternal lineage. The polyploids Sorbus eminens, Sorbus porrigentiformis, and S. latifolia have multiple maternal lineages. The two primary diploid hybrids S. × thuringiaca and S. × vagensis have arisen many times independently. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 154, 291–304.

Teodor Hedlund was a Swedish botanist who published nearly 50 new names or combinations in Sorbus L. (Rosaceae). Lectotypes are designated for Sorbus arranensis Hedlund, S. minima (Ley) Hedlund, S. quercifolia Hedlund and S. subsimilis Hedlund. The lectotypification of S. anglica Hedlund by A. J. Wilmott is rejected and a new lectotype selected. Notes are given on typification of S. rupicola (Syme) Hedlund. "Sorbus globulifera Hedlund ex Riddelsdell" is not validly published and the material it is based on is part of the variation in S. aria (L.) Crantz.

The uncommon spontaneous hybrid between Sorbus aucuparia L. and S. intermedia (Ehrh.) Pers (Rosaceae) is described and named as Sorbus×liljeforsii.