Pink Knotweed (Persicaria capitata), found growing in a bed of Lesser Periwinkle (Vinca minor) in some landscaping in downtown Sunnyvale, CA. The Lesser Periwinkle (shiny, elliptical, green leaves) was planted, there, but the Pink Knotweed (matte, ovate, dull green leaves with pinkish tones, reddish margins reddish veins, and dark, chevron-shaped markings) was what gardeners call a "volunteer" or a "waif." Although it is a popular ornamental ground cover, pink knotweed is highly invasive, and can rapidly take over an entire area.

The first photo of this set is a closeup of some flowers and leaves. The second is a wider view of the plant, which is (oddly) better for examining its field marks. The third photo of this set is a marked-up version of the second, showing some of the plant's key field marks.