Roses don't have thorns: those spikes are prickles, and one gene controls them
The sharp hooks on a rose stem are not true thorns, which grow from modified stems, but prickles sprouting from the skin of the plant. They help roses clamber over neighbours, and a geneticist found that silencing a single gene, called LOG, shrinks them to tiny buds. Many garden roses cannot even set seed.
Roses belong to the genus Rosa in the family Rosaceae. Counts of species vary, from 140 to 180 in one reckoning to over three hundred in another, with tens of thousands of cultivars. Most wild species come from Asia, fewer from Europe, North America and northwest Africa. The plants range from trailing shrubs to climbers reaching 7 metres, and most shed their leaves in winter, though some Southeast Asian species stay green.
Wild flowers usually have five two-lobed petals, often white or pink; Rosa omeiensis and Rosa sericea typically manage only four. Insects pollinate them, and a fertilised flower swells into a hip holding anything from 5 to 160 tiny dry fruits wrapped in stiff hairs. Hips of the dog rose and rugosa rose rank among the richest plant sources of vitamin C, and thrushes and waxwings spread the seeds. Densely packed straight prickles on dune species such as Rosa rugosa may deter grazers or trap blowing sand to protect roots, though deer browse roses regardless.
The fossil record goes back to the Late Eocene Florissant Formation in Colorado, and roses had reached Europe by the early Oligocene. People have grown them for ornament since at least 500 BC around the Mediterranean, in Persia and in China. Modern garden roses descend largely from Rosa chinensis, imported from China in the eighteenth century, and genome studies suggest domestication favoured genes for DNA repair and stress tolerance, perhaps because constant hybridising shook up their chromosomes.
Breeders have produced an estimated 30 to 35 thousand hybrids and cultivars, mostly double-flowered because stamens have turned into extra petals; tightly packed blooms often block pollinators, so these can only be propagated by cuttings. Empress Josephine sponsored rose breeding at Malmaison in the early nineteenth century, and by 1840 an English cemetery rosarium held more than a thousand kinds. Today cut roses are often raised in greenhouses or in tropical countries and flown to markets worldwide.
Source: Rose
