I am being perhaps unreasonably picky here since I can't find a leaf structure in any of the plant pictures suggested that matches the leaf structure above, that triangular stem and then the leaves growing out through the stem.

Thanks for the input. Whatever comprises that plant structure (whether stems or leaves), I haven't seen any pictures of mature plants that show that sort of broad spreading vegetation, though I've seen spikey growth and even vine-like growth on various species. Maybe you're right, that there's no way to ID it by the vegetation alone.

I suppose I'll have to just wait until Spring if I can keep it alive that long, and if it blooms, there might be a better chance of IDing it.