Aplotaxene, a possible allelochemical of thistle (Carduus sp)

• EMBRAPA/Environment, Jaguariuna, SP 13820, Brazil • Faculty of Agronomic Sciences, Sao Paulo State University, Botucatu, SP 18610 Brazil • Esalq, Universidade de Sao Paulo, Piracicaba, SP 13418, Brazil • NPURU/USDA/ARS, University, MS 38677, USA • Faculdade de Farmacia, Universidade Federal Fluminense, Niteroi, RJ 24241, Brazil • Department of Biology, The Pennsylvania State University, University Park, PA 16802, USA