Croftonweed has established itself as a pernicious weed in China. Experiments were conducted to test for anemophily, self-pollination, hand crossing, and apomixis. Additionally, pollen viability, seed set, and seed viability were investigated. Pollen cultured in vitro with the use of 14 culture media did not germinate, nor did self- or cross-pollen germinate on the stigma, and no pollen tubes were seen in the style. Young embryos developed into globular- or heart-shaped embryos before the opening of the captimulum, although neither meiosis to form an embryo sac nor fertilization occurred. Furthermore, seeds developed normally after closed flowers were emasculated and bagged. The plump seed ratio (plump seeds/total seeds) from apomixis (emasculation and bagged treatment) was high (41 ± 17.0%), and plump seed germination ratio exceeded 50%. These results provided additional evidence for the previous conclusion that croftonweed reproduces by apomixis. Apomixis, high seed production, and high seed germination may explain why this weed spreads so rapidly.

Nomenclature: Croftonweed, Eupatorium adenophorum Spreng EUPAD.