Vegetative and reproductive growth of an invasive weed Bidens pilosa L. var. radiata and its noninvasive congener Bidens bipinnata in Taiwan.
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.