Beautiful Roses

Roses are red 'to deter, not to attract'

Scientists have discovered why roses are red, claiming their striking colour has evolved to deter predators

Red rose: 'The colour red acts as a warning to large vertebrate herbivores like emus, parrots and kangaroos' Photo: CLARA MOLDEN

Naturalists have always believed that flowers had developed a bright and vibrant appearance to attract insects, mammals and birds needed for cross-pollination. But biologists from three universities have published a report which disproves the theory - claiming the striking red colour deters herbivores because of high cyanide levels.

The team studied plants in Western Australia and found the need to defend themselves against predators has been a major factor in their evolution. Experts from the Universities of Plymouth and Portsmouth and Curtin University, in Western Australia discovered consistently higher levels of cyanide in the large, red flowers - such as roses and poppies - which commonly employed by plants to deter herbivores.

As cyanide is commonly employed by plants to deter herbivores, they believe this proves that bird-pollinated flowers have evolved as a response to herbivore attack. The close association between red flowers, bird-pollination and high floral cyanide levels also suggests a second major revision of how biologists must now view floral evolution.

Dr Mick Hanley, a leading scientist in the study, says this shows that animals that eat the plants learn to associate the colour with the bitter taste produced by cyanide. He said: "The colour red acts as a warning to large vertebrate herbivores like emus, parrots and kangaroos that the flower contains distasteful or even poisonous cyanogenic compounds.

"It seems that Western Australian plants have not only developed a remarkable defence against would-be flower predators, but that they also clearly advertise the fact." They collected 50 different species of hakea, a group of plants which are noted for their diverse appearance.

The research - published in this month's edition of New Phytologist - was funded by a British Ecological Society Small Ecological Project Grant.