Mine produces a few isolated flowers early in the summer, but starts blooming more profusely around August. Strophostyles leiosperma has been bloom the last month also. Strophostyles leiosperma looks identical to the other two, but much smaller, so it is easy to distinguish.
Here is a pic of S. leisosperma and my unidentified one to show the difference in size.
The picture below is of the subtending bract I mentioned as the only way to tell umbellata and helvola apart. But I have found nothing to explain how this part is different in the two plants.
