That people around the world find flowers beautiful is unquestionable, but we understand surprisingly little about why this is so. Scientists remain puzzled by phytophilia - the human love of flowers.
The habitat selection theory proposes that attraction to flowers was an adaptive trait of such benefit it has now become hard-wired in us. Our ancestors' survival depended on their ability to choose safe and abundant places to live and a wide variety of flowers advertises a rich habitat and the likelihood of edible fruits and tubers.
Flower signs had to be visible from a distance, which probably explains why most people show a preference for clear, vivid colours. Blue is the most popular flower colour across almost all cultures. This might be because blue is the least common colour for flora and fauna and therefore easy to spot, or it might be because we subconsciously associate blue with clean water and sunny skies - people also tend to rate birds with blue feathers as more attractive than birds of other colours.
Maroon, olive green and brown flowers are generally the least preferred, probably because of the subconscious association between these colours and rotting vegetation. More mysterious is the reason why yellow also tends to score comparatively low on people's flower colour preferences.
Some colour preferences definitely include a cultural component. For example, people living in Asian countries report an unusually high preference for white flowers, associating them with serenity and purity, particularly in the context of religious rituals. In Western Europe and the USA women report an unusually high preference for pastel shades such as pink and lilac - colours we are conditioned to associate with femininity and prettiness.
However, a 2006 study by Czech scientists revealed that shape influences our flower preferences even more strongly than colour. This mirrors findings about human beauty - in most cultures bone structure and facial symmetry have greater impact than colouring on perceived attractiveness.
When it comes to the shape of a flower, people generally like a soft, rounded outline of medium complexity. Sharp, jagged shapes seem to evoke ancient, subconscious feelings of wariness (think thorns, horns, spikes and canines). Convoluted and irregular shapes are disliked because they cannot easily be identified and categorised by the brain, whilst very simple shapes are perceived as plain boring. This could explain why the rose, the lily, the peony and the tulip dominate the popularity charts, consistently reported as more beautiful than say, the thistle at one end of the spectrum (spiky and complex) and the daisy at the other (simple and unstimulating).
A third factor in our flower preference is perfume. When we are drawn to a flower's shape and colour, fragrance amplifies our liking - people almost always rate a scented rose above one with little fragrance. However, scent on its own is rarely enough to influence overall preference. Although favourite reported scents include lavender, honeysuckle, hyacinth, lilac and violet, few people rank these flowers as among the most attractive. In 2016 2,000 people in the UK were asked to identify their favourite three flowers. The results were as follows: