lobelia stems, noticed

Looking out my home office window I see my walkway garden, complete with bird feeder and the I'm-not-letting-it-freeze water barrel. The combination of these two means that quite often there's something to see when I glance out there -- the birds are always fun to watch.

The other day I noticed something different though: my lobelia (Lobelia cardinalis), stems dead and dried at this time of year, looked strange.

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Not down there where the basal growth lets me know that this plant is coming back strong in the spring, but up here where spring is nowhere to be seen:

There was something about the way that the light was hitting some of the stems... I realized that they were flattened and strangely wide:

I don't remember seeing this while the stems were still alive, but the foliage and flowers may have distracted me.

There were a couple of other wide stems too, but not all of them showed this feature:

Was this caused by one of the recent freezes, or did this occur while the plant was still growing?  I'm guessing freezes, but I can't see any splits or cracks -- any thoughts?

This walkway project was the best thing I've done to my garden in the last few years. Always interesting, always surprising!

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