The European dogroses, including Rosa canina, belong to Rosa section Caninae. One feature defining section Caninae is revealed in the solution to an old, familiar riddle:
On a summer's day, in sultry weather,
Five brethren were born together.
Two had beards and two had none,
And the other had but half a one.
The answer is the five sepals of the dogrose calyx, which for the brief flowering period are usually hidden by five petals. Evocatively-scented dogrose flowers are a transient summer feature of hedges and waste places in Europe, North Africa and western Asia. The petals soon fall but the sepals often persist as the ovaries mature into bony fruits, surrounded by short, stiff hairs, within a brightly coloured rosehip. As syrup, rosehips have been used as food supplements, whilst crushed rosehips make effective itching powder for childhood pranks. However, the quality of rosehip syrup, but not itching powder, is highly variable, as vitamin C content varies with rosehip source and harvest time, and cooking temperature and duration.
Subtle morphological variation in dogroses has been known for centuries. In 1724, Johann Dillenius described a dogrose the apothecary James Sherard discovered near Kingston-upon-Thames. In 1800, botanist James Smith was unsure and thought it merely a variant of another dogrose. However, in 1813, following extensive field experience in Wales, Hugh Davies formally described Rosa sherardii in Sherard's honour. Davies was circumspect, declaring 'no one, who has paid much attention to this most variable genus, will expect to find even a small number of the same species agree in every particular'. The nineteenth century saw a proliferation of species names, as hundreds of dogroses were formally described. Today, only a handful of dogrose species are recognised.
During the early twentieth century, the biological basis of dogrose variation was revealed. In Britain, John Heslop-Harrison and his European colleagues undertook pioneering work on rose cytology. They showed chromosome separation, during pollen and egg (gametes) formation, was unusual and that hybridization was both frequent and widespread. With five complete chromosome sets, dogroses might be expected to produce sterile gametes. However, during gamete formation, chromosomes separate such that the dogrose embryo has one set of chromosomes from its father and four sets of chromosomes from its mother. Understanding such behaviour has been important for disentangling the multitude of names applied to the dogroses, explaining natural rose variation and breeding new rose variants for the horticultural market.
Graham GG, Primavesi AL (993. Roses of Great Britain and Ireland. Botanical Society of the British Isles.
Stearn WT (1965) The five brethren of the rose: an old botanical riddle. Huntia 2: 180-184.