As an aromatherapist, the tools of my trade are very dependent on the sun. Most essential oil bearing plants produce more essential oil and a more concentrated oil during hotter weather though it should be noted that some oils such as high altitude lavender are of a higher and or different quality. Thyme for instance has a varying chemical composition with differing therapeutic properties depending on the altitude and therefore temperature and light conditions where they are grown.
These essential oils can come from any part of the plant. Flowers and leaves are perhaps the best known and the citrus family can produce three different oils all from the same plant, each having a different function in nature. Neroli from the flowers attracts pollinating insects, petigrain comes from the leaves and serves to deter insects from eating them. The third essential oil comes from the zest of the fruit and encourages birds along with small and larger mammals (such as ourselves) to eat them and in doing so spread the seeds. Many other oils come from the wood of trees, pine, spruce, sandalwood, and rosewood are all examples of this. Finally, there are the roots, horseradish produces mustard oil designed to stop the roots being eaten! Perversely, that oil is why humans do eat it! Vetiver and a few other plants produce essential oils that are widely used in aromatherapy.
Of course, the vegetable oils coconut, walnut and others (every therapist has their own favourites) are just as dependent on the sun and have their own nourishing properties that they bring to a massage.
I often remember how dependent on the sun we are when I am preparing for an aromatherapy appointment with a client and think about how I can best transfer that energy to them.