Amy Brooke asks :-

It is said that plants give off a perfume to attract insects to pollinate them. However any one species, e.g. roses, have a range of different smells and they get pollinated. Is there a reason plants from the same species have a variety of smells?

Janice Lord, a botanist at the University of Otago, responded.

Flowers produce a huge variety of volatile compounds from deliciously pleasant, such as the damask rose, to positively noxious, such as the Titan Arum which flowered in the Dunedin Botanic Gardens earlier this year. These different scent profiles relate very strongly to the types of pollinators that are attracted to the flower. In the case of wild roses, these pollinators are nectar and pollen feeding insects such as bees, and in the case of Titan Arum, they are beetles and flies that lay their eggs on rotting meat.

Studies of floral scent variation in both wild and cultivated species have found large differences between plants of the same species. Some of these differences relate to flower age or plant health, however time of day, temperature and humidity also affect scent production. However, even when these factors are controlled as much as possible, floral scent can still vary among plants of the same species because pollination is in reality a competition. The plant that has the most attractive scent is visited by the most pollinators, so has a greater reproductive success.

The roses in your garden have more capacity for variation in fragrance than a single species as they originated from hybrids between different wild rose species, which themselves differed in scent profiles. Thus it is not surprising that they can vary as widely in fragrance as they do in colour and form. The famous Damask rose that has contributed extensively to the development of modern roses is itself thought to be an ancient hybrid between the wild species Rosa gallica, Rosa moschata and Rosa fedchenkoana originating in the foothills of central Asia possibly more than two thousand years ago. The fragrant legacy of this rose can still be detected in some modern cultivars with large, many-petalled, deep red or pink flowers.

Send questions to: Ask-A-Scientist, PO Box 31-035, Christchurch 8444 Or email: questions@ask-a-scientist.net