We live in central Alabama and have a plant taking over a mostly-empty mulched bed. I would like to remove it, and it would help to know what it is and any advice on removal. It appears to prefer sunlight, and hardly grows in parts of the bed that are shaded, but grows very quickly and densely in well-lit parts.
The plant grows just under 2 feet (~60 cm) high. It has opposing pairs of pinnate leaves along the stem, which alternate 90 degrees each pair. At the top of the stem is a very small white flower with about a dozen petals. The stems are quite fragile and break easily, which make pulling it challenging.
The plant puts out runners which are reddish, and this appears to be a mode of reproduction. It also grows roots that go down about 2-4 inches and then grow horizontally. At least one root I pulled out was about a foot long (~30 cm) and one half inch (~1 cm) thick. The runners and stems tend to form dense knots at ground level, where they emerge from the top of the root.
What is this plant and how can I remove it effectively?
