Effects of seed characteristics and germination on invasiveness of Ageratina adenophora Analysis of PCBs in the sediments and fish from freshwater fishponds in the Pearl River Delta, China Toxicity risks to the closed tidal flat ecosysten of a PCBs waste savepoint at the coast of Zhejiang Pre- and post-zygotic reproductive isolation between co-occurring Mussaenda pubescens var. alba and M. shikokiana (Rubiaceae)