Cycads: evolutionary innovations and the role of plant-derived neurotoxins.

Cycads are an important relic from the past and represent the oldest living seed plants. Cycads have been instrumental in our understanding the evolution of angiosperms and gymnosperms because they have recognizable morphological characteristics intermediate between less-recently evolved plants such as ferns and more-derived (advanced) plants including the angiosperms. Cycads also produce several compounds that are carcinogenic and neurotoxic. Because of their unique placement in terrestrial plant evolution, molecular studies should help to define the origins of structures that led to the rise of seed plants and the role of neurotoxic compounds that are found in cycads.