Isn't that interesting?.?. While I have no answer for you, I personally have found that during the normal outdoor growing season, plants with purple foliage are not nearly as vigorous as those with green. Maybe the darker leaves do make a huge difference when the temps turn cold.

Need a photo. Can't begin to tell you what it might be just based on that description.

Also in the top picture is foliage from a Callistemon (shrub) if you are interested. Regarding the Lysimachia - it rather depends on your gardening style as to whether you would consider it a terrible pest. If you are into neatness and control, maybe. If you like a more organic and free-flowing garden give it a chance. You can always pull out bits you don't want. Lysimachia ciliata 'Firecracker'

You got it carol. We have a lot of Justicia americana here. I've been looking for Justicia ovata for 3 years, always searching around water, and never expected to find it in a modestly damp ditch. I was also looking for a much larger plant. Thanks for the help.