A single phytoalexin was isolated and purified from 12- to 14-day-old leaves of Cassia obtusifolia L. inoculated with Alternaria cassiae Jurair & Khan. The structure was elucidated by (1)H- and (13)C-nuclear magnetic resonance and mass spectrometry as 2-(p-hydroxyphenoxy)-5,7-dihydroxychromone. The