Plant olfaction - Plants smell?

Common dodder (Cuscuta pentagona)

Cuscuta pentagona is not your normal plant. It is a spindly orange vine that it basically has no leaves. What's unique about Cuscuta is that it isn’t green, because it lacks chlorophyll, the pigment that absorbs solar energy, allowing plants to turn light into sugars and oxygen through photosynthesis. Cuscuta gets its food from its neighbors; it is a parasitic plant. In order to live, Cuscuta attaches itself to a host plant and sucks off the nutrients provided by the host by burrowing an appendage into the plant’s vascular system. What makesCuscuta truly fascinating is that it has culinary preferences: it chooses which neighbors to attack.

The way Cuscuta does this is through its sense of smell. Yes Cuscuta, like all plants, can sense volatile chemicals in the air, just like we can sense, can smell, bleach that's been used to wash a floor, a neighbor's barbecue a few houses down the street, or a new perfume squirted into the air. Cuscuta uses the smell of neighboring plants to find the tastiest one to attach on to. Cuscuta tells the difference between plants by the way they smell; Cuscuta can differentiate between tomato and wheat, and given the choice will prefer a tomato plant!

You can read more about Cuscuta and a plant's sense of smell here, or in Chapter 2 of WHAT A PLANT KNOWS.