Plant tropisms: from Darwin to the International Space Station.

Plant tropisms play a fundamental role in shaping the growth form of plants, and these fascinating movements are the focus of this thematic issue of the American Journal of Botany. The issue includes 16 reviews of the current literature and eight original manuscripts written by a diverse group of international experts in their respective fields. This special issue emphasizes tropistic responses to three fundamental stimuli governing plant growth: water, light, and gravity. We hope this issue will inform the current generation and inspire the next generation of plant biologists.