Different flowers have different smells? Why?

C. GEORGE VARGHESE

Thrissur, Kerala

Each flower or the flower family has an aroma (smell). Chemical substances in the plant species contribute to the smell of the flowers, leaves, roots or even fruits. These chemical substances are mostly low molecular weight compounds and volatile in nature so that they could easily spread, and be perceived.

Terpenes and esters are some of the commonly known chemicals that constitute the floral fragrance. However, the foul smelling flowers may have different chemicals including sulphides, amines, phenols, etc. Several compounds may occur in the same plant species and the flower smell between the plant species might vary depending on the chemical constituents and their concentration.

In pollination, the pollen grains (male part) should be transferred to the stigma (female part) of the same flower or different flowers of the same plant species. The organisms that usually get involved in pollination are known as pollinators and they could be insects, birds, etc. These pollinators are usually attracted by the smell and colour of a flower. If all the flowers produce a similar aroma, and if all the pollinators prefer all kinds of smells, there is no reproductive advantage for those flowering plants.

On the other hand, when a flower can differentiate itself from other species by its unique smell and colour, it increases its likelihood to attract more specialized pollinators that could maximize its reproductive success through enhanced pollination. It has evolved in nature through a process called ‘co-evolution’ in which a flower species and its pollinator species adapt to each other’s changes over a long period of time.

Some flowers produce a foul smell like rotting meat, because they are usually pollinated by flies and beetles. Thus, the flower smell is mainly determined by its chemical constituents, and the smell has mainly evolved to attract its preferred pollinators.

Dr. R. SRINIVASAN

Entomologist and Head of Entomology Group

AVRDC-The World Vegetable Center

Tainan, Taiwan

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