Horticulture is my blind spot

I'm hoping that someone can identify this plant for me. Specifically, I am wondering if it is a weed: We had our front lawn replaced with a rock garden and some perennials last fall. The Gambler thinks that this is something that was planted, but I really don't think so (we didn't do the planting). It is creeping along the ground in a very weed-like manner, and there is no sign of any type of flower. It actually looks kind of sinister with its thick red stems - I have visions of it reaching out and grabbing my ankles. I have tried various "weed identification" websites to no avail. And if I enter "weed black spot" into Google, I find all sorts of useful information about how to deal with a fungus that affects marijuana plants, but I am no further ahead in figuring this thing out. Even if it's not a weed, I really don't like the look of the thing, but I hate to rip it out if it is just in an ugly duckling stage.