本文比較在臺灣共域、同屬的大花咸豐草(Bidens pilosa L. var. radiata)(入侵植物)和鬼針草(B. bipinnata L.)(歸化植物)的光合作用表現、種子發芽率、營養生長、以及繁殖生長能力；目的在瞭解大花咸豐草能在台灣快速擴散的生物特徵。結果發現：兩者在光合作用表現上沒有顯著差異，但在不同溫度下的種子發芽率、營養繁殖能力以及生物質量的分配上有顯著差異。鬼針草的種子在冬天低溫(18°C)下發芽率明顯受到抑制，大花咸豐草則無此現象。相較於鬼針草，在幼苗生長時期大花咸豐草有較大的單位乾重葉面積比、把較多的資源分配到葉和根部，因此生長較快，以致在成株時可以累積較多的生物量。又大花咸豐草的分枝可以長不定根形成一新的植株，而鬼針草則無此能力。上述特徵差異可以解釋當大花咸豐草和鬼針草共域時，鬼針族群數量減少的原因；有較大的單位乾重葉面積比、把較多的資源分配到葉和根部、生長較快、種子發芽不受低溫影響、有營養繁殖能力(莖會長不定根)等這些特徵也可能是導致大花咸豐草能在台灣快速擴散的生物因素。

To gain a better understanding of traits and mechanisms underlying the fast spreading of an invasive plant, B. pilosa var. radiata, in Taiwan, we compared vegetative and reproductive growth of this invasive plant with its sympatric congener Bidens bipinnata L., a naturalized species. The two species had similar photosaturated photosynthetic rate and apparent quantum yield. However, both species differed in the temperature response of seed germination, in traits associated with life history, and in biomass allocation pattern. At winter temperature (18°C) seed germination was inhibited in B. bipinnata but not in B. pilosa var. radiata. Compared to B. bipinnata, B. pilosa var. radiata had higher specific leaf area, allocated more resource to leaves and roots in early growth stage, consequently, had a better growth and accumulated more biomass for an extended growth period. Laboratory experiment showed that shoot segments of B. pilosa var. radiata were capable of growing adventitious roots while those of B. bipinnata had no such ability. Thus, differences in specific leaf area, pattern of biomass allocation, seed germination response and vegetative reproduction between these two species explained why B. pilosa var. radiata outcompeted B. bipinnata in the field.