Photographed in the Butterfly Meadow. Although this plant looked familiar, I couldn't place an ID on it, but thanks to Claudia, I now know it is Wild Senna, a plant native to the eastern US, and perhaps southern Ontario. It is a perennial which spreads rapidly, apparently, and grows to 6 feet. It was not planted in the Butterfly Meadow, but appeared there this summer. Claudia says it was planted in the Backyard Garden some years ago, so that may be the source for this plant.