Arabidopsis thaliana isolates from the wild vary enormously in their morphology and physiological responses to standard conditions, indicating that substantial genetic variation is accessible in this species. Natural variant alleles encoding two Arabidopsis photoreceptors, phytochrome A and cryptochrome 2, have now been identified by different experimental methods. The amino-acid substitutions suggest new features of phytochrome and cryptochrome function that regulate plant growth and flowering time.