The study of flower structure is essential in plant identification and in understanding sexual reproduction in plants, pollination syndromes, plant breeding, and fruit structure. Thus, study of flower structure and construction of floral formulae are standard parts of first-year university botany and biology courses. These activities involve developing a complex set of skills, and it is useful for students to review this material after practical sessions. The Virtual Floral Formula Web site provides students with a unique resource for practicing their floral structure interpretation skills. The site provides detailed dissection photographs of the flowers of 12 species, and floral formulae are progressively assembled via drop-down menus. When students are satisfied with their answers, they submit them, and any discrepancies from the "official" formula are highlighted. Students appreciate the interactivity of the application, the feedback they receive on any inaccuracies in their formulae, and the ability to make progressive improvements in their skills.