One espresso please…

Why do plants produce caffeine in the nectar? This is indeed an intriguing question!
Check out this nice post on the flowering newsletter, and here some related papers:

Adler LS. (2000), The ecological significance of toxic nectar. Oikos, 91: 409–420. doi: 10.1034/j.1600-0706.2000.910301.x

Chittka L and Peng F. Caffeine Boosts Bees’ Memories. Sciences. 2013. Vol. 339 no. 6124 pp. 1157-1159. DOI: 10.1126/science.1234411

Wright GA, Baker DD, Palmer MJ, Stabler D, Mustard JA, Power EF, Borland AM, Stevenson PC. Caffeine in Floral Nectar Enhances a Pollinator’s Memory of Reward. Science. 2013. Vol. 339 no. 6124 pp. 1202-1204.

Pollan M. The Botany of Desire (2001). Random House, hardcover: ISBN 0-375-50129-0, 2002 paperback: ISBN 0-375-76039-3