Citation: Ziska, L.H., Tomecek, M.B., Gealy, D.R. 2014. Assessment of cultivated and wild, weedy rice lines to concurrent changes in CO2 concentration and air temperature: Determining traits for enhanced seed yield with increasing atmospheric CO2. Functional Plant Biology. 41:236-243. Interpretive Summary: Although carbon dioxide (CO2) is a greenhouse or warming gas, it is also the source of carbon for plant growth. Consequently its increase in the atmosphere represents an opportunity to exploit CO2 or utilize CO2 more effectively to increase seed yields. One means to exploit CO2 is to screen crop varieties so as to determine which one is best able to convert additional CO2 into more seed yield. We did this for rice, a primary source of calories globally, using four different lines, including a wild, or weedy line, "StgS". We found that while all lines responded with more seed yield as CO2 increased; as temperature increased, the stimulation of seed yield by CO2 declined. The exception however was the weedy line, "StgS" which increased seed yields even at day/night temperatures up to 33/25oC. In examining how this weedy rice line was able to do this, we discovered a good correlation between the ability of varieties to develop stems (tillers) early on, and the response of seed yield to CO2/temperature. Our results suggest that including novel genes from weedy lines could help in adapting crops like rice to future climate change; and that early differences in tiller formation may be one way to determine which lines are better able to exploit, or convert CO2 into seed yield. This information will be of interest to plant breeders, plant scientists and those interested in climate change and food security.