Thanks Fatamorgana. I'm not sure on the leaf -- my leaf looks like it has more of an "indent" at the base than either the mulberry or the basswood in the pics you linked. it actually looks more like the redbud leaf, but i think those leaves are much smaller? #2 did not smell like mint. I have left it in for now to see if it flowers. I pulled out all of #1 (commelina). I have a new pic of #6. underneath the leaves is a cluster of what looks like small flower buds developing -- does this help with an ID? Thank you!

It was explained to me when I visited that a few plants were planted around this water feature and those plants have grown each year and expanded. Some have now run into one another and covered certain areas.

#1 could be a variety of Lamium galeobdolon #2 is Lamium maculatum #3 looks like Corydalis lutea

Yes, baccharis. During an earlier let's plant this thing everywhere cycle in CA, the most used were the horizontal spreaders, such as 'Pigeon Point'. The spreaders are happy to get 3-4' tall, although they tended to be advertised as 2'ers. I'm not sure what cultivars are popular right now, as I haven't planted baccharis in many years. They have their place and use, and are very good at certain tasks, but I think they are rather boring.